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TOMOYO Linux Cross Reference
Linux/fs/xfs/xfs_log_cil.c

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  1 // SPDX-License-Identifier: GPL-2.0
  2 /*
  3  * Copyright (c) 2010 Red Hat, Inc. All Rights Reserved.
  4  */
  5 
  6 #include "xfs.h"
  7 #include "xfs_fs.h"
  8 #include "xfs_format.h"
  9 #include "xfs_log_format.h"
 10 #include "xfs_shared.h"
 11 #include "xfs_trans_resv.h"
 12 #include "xfs_mount.h"
 13 #include "xfs_extent_busy.h"
 14 #include "xfs_trans.h"
 15 #include "xfs_trans_priv.h"
 16 #include "xfs_log.h"
 17 #include "xfs_log_priv.h"
 18 #include "xfs_trace.h"
 19 
 20 struct workqueue_struct *xfs_discard_wq;
 21 
 22 /*
 23  * Allocate a new ticket. Failing to get a new ticket makes it really hard to
 24  * recover, so we don't allow failure here. Also, we allocate in a context that
 25  * we don't want to be issuing transactions from, so we need to tell the
 26  * allocation code this as well.
 27  *
 28  * We don't reserve any space for the ticket - we are going to steal whatever
 29  * space we require from transactions as they commit. To ensure we reserve all
 30  * the space required, we need to set the current reservation of the ticket to
 31  * zero so that we know to steal the initial transaction overhead from the
 32  * first transaction commit.
 33  */
 34 static struct xlog_ticket *
 35 xlog_cil_ticket_alloc(
 36         struct xlog     *log)
 37 {
 38         struct xlog_ticket *tic;
 39 
 40         tic = xlog_ticket_alloc(log, 0, 1, XFS_TRANSACTION, 0,
 41                                 KM_NOFS);
 42 
 43         /*
 44          * set the current reservation to zero so we know to steal the basic
 45          * transaction overhead reservation from the first transaction commit.
 46          */
 47         tic->t_curr_res = 0;
 48         return tic;
 49 }
 50 
 51 /*
 52  * After the first stage of log recovery is done, we know where the head and
 53  * tail of the log are. We need this log initialisation done before we can
 54  * initialise the first CIL checkpoint context.
 55  *
 56  * Here we allocate a log ticket to track space usage during a CIL push.  This
 57  * ticket is passed to xlog_write() directly so that we don't slowly leak log
 58  * space by failing to account for space used by log headers and additional
 59  * region headers for split regions.
 60  */
 61 void
 62 xlog_cil_init_post_recovery(
 63         struct xlog     *log)
 64 {
 65         log->l_cilp->xc_ctx->ticket = xlog_cil_ticket_alloc(log);
 66         log->l_cilp->xc_ctx->sequence = 1;
 67 }
 68 
 69 static inline int
 70 xlog_cil_iovec_space(
 71         uint    niovecs)
 72 {
 73         return round_up((sizeof(struct xfs_log_vec) +
 74                                         niovecs * sizeof(struct xfs_log_iovec)),
 75                         sizeof(uint64_t));
 76 }
 77 
 78 /*
 79  * Allocate or pin log vector buffers for CIL insertion.
 80  *
 81  * The CIL currently uses disposable buffers for copying a snapshot of the
 82  * modified items into the log during a push. The biggest problem with this is
 83  * the requirement to allocate the disposable buffer during the commit if:
 84  *      a) does not exist; or
 85  *      b) it is too small
 86  *
 87  * If we do this allocation within xlog_cil_insert_format_items(), it is done
 88  * under the xc_ctx_lock, which means that a CIL push cannot occur during
 89  * the memory allocation. This means that we have a potential deadlock situation
 90  * under low memory conditions when we have lots of dirty metadata pinned in
 91  * the CIL and we need a CIL commit to occur to free memory.
 92  *
 93  * To avoid this, we need to move the memory allocation outside the
 94  * xc_ctx_lock, but because the log vector buffers are disposable, that opens
 95  * up a TOCTOU race condition w.r.t. the CIL committing and removing the log
 96  * vector buffers between the check and the formatting of the item into the
 97  * log vector buffer within the xc_ctx_lock.
 98  *
 99  * Because the log vector buffer needs to be unchanged during the CIL push
100  * process, we cannot share the buffer between the transaction commit (which
101  * modifies the buffer) and the CIL push context that is writing the changes
102  * into the log. This means skipping preallocation of buffer space is
103  * unreliable, but we most definitely do not want to be allocating and freeing
104  * buffers unnecessarily during commits when overwrites can be done safely.
105  *
106  * The simplest solution to this problem is to allocate a shadow buffer when a
107  * log item is committed for the second time, and then to only use this buffer
108  * if necessary. The buffer can remain attached to the log item until such time
109  * it is needed, and this is the buffer that is reallocated to match the size of
110  * the incoming modification. Then during the formatting of the item we can swap
111  * the active buffer with the new one if we can't reuse the existing buffer. We
112  * don't free the old buffer as it may be reused on the next modification if
113  * it's size is right, otherwise we'll free and reallocate it at that point.
114  *
115  * This function builds a vector for the changes in each log item in the
116  * transaction. It then works out the length of the buffer needed for each log
117  * item, allocates them and attaches the vector to the log item in preparation
118  * for the formatting step which occurs under the xc_ctx_lock.
119  *
120  * While this means the memory footprint goes up, it avoids the repeated
121  * alloc/free pattern that repeated modifications of an item would otherwise
122  * cause, and hence minimises the CPU overhead of such behaviour.
123  */
124 static void
125 xlog_cil_alloc_shadow_bufs(
126         struct xlog             *log,
127         struct xfs_trans        *tp)
128 {
129         struct xfs_log_item     *lip;
130 
131         list_for_each_entry(lip, &tp->t_items, li_trans) {
132                 struct xfs_log_vec *lv;
133                 int     niovecs = 0;
134                 int     nbytes = 0;
135                 int     buf_size;
136                 bool    ordered = false;
137 
138                 /* Skip items which aren't dirty in this transaction. */
139                 if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
140                         continue;
141 
142                 /* get number of vecs and size of data to be stored */
143                 lip->li_ops->iop_size(lip, &niovecs, &nbytes);
144 
145                 /*
146                  * Ordered items need to be tracked but we do not wish to write
147                  * them. We need a logvec to track the object, but we do not
148                  * need an iovec or buffer to be allocated for copying data.
149                  */
150                 if (niovecs == XFS_LOG_VEC_ORDERED) {
151                         ordered = true;
152                         niovecs = 0;
153                         nbytes = 0;
154                 }
155 
156                 /*
157                  * We 64-bit align the length of each iovec so that the start
158                  * of the next one is naturally aligned.  We'll need to
159                  * account for that slack space here. Then round nbytes up
160                  * to 64-bit alignment so that the initial buffer alignment is
161                  * easy to calculate and verify.
162                  */
163                 nbytes += niovecs * sizeof(uint64_t);
164                 nbytes = round_up(nbytes, sizeof(uint64_t));
165 
166                 /*
167                  * The data buffer needs to start 64-bit aligned, so round up
168                  * that space to ensure we can align it appropriately and not
169                  * overrun the buffer.
170                  */
171                 buf_size = nbytes + xlog_cil_iovec_space(niovecs);
172 
173                 /*
174                  * if we have no shadow buffer, or it is too small, we need to
175                  * reallocate it.
176                  */
177                 if (!lip->li_lv_shadow ||
178                     buf_size > lip->li_lv_shadow->lv_size) {
179 
180                         /*
181                          * We free and allocate here as a realloc would copy
182                          * unnecessary data. We don't use kmem_zalloc() for the
183                          * same reason - we don't need to zero the data area in
184                          * the buffer, only the log vector header and the iovec
185                          * storage.
186                          */
187                         kmem_free(lip->li_lv_shadow);
188 
189                         lv = kmem_alloc_large(buf_size, KM_NOFS);
190                         memset(lv, 0, xlog_cil_iovec_space(niovecs));
191 
192                         lv->lv_item = lip;
193                         lv->lv_size = buf_size;
194                         if (ordered)
195                                 lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
196                         else
197                                 lv->lv_iovecp = (struct xfs_log_iovec *)&lv[1];
198                         lip->li_lv_shadow = lv;
199                 } else {
200                         /* same or smaller, optimise common overwrite case */
201                         lv = lip->li_lv_shadow;
202                         if (ordered)
203                                 lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
204                         else
205                                 lv->lv_buf_len = 0;
206                         lv->lv_bytes = 0;
207                         lv->lv_next = NULL;
208                 }
209 
210                 /* Ensure the lv is set up according to ->iop_size */
211                 lv->lv_niovecs = niovecs;
212 
213                 /* The allocated data region lies beyond the iovec region */
214                 lv->lv_buf = (char *)lv + xlog_cil_iovec_space(niovecs);
215         }
216 
217 }
218 
219 /*
220  * Prepare the log item for insertion into the CIL. Calculate the difference in
221  * log space and vectors it will consume, and if it is a new item pin it as
222  * well.
223  */
224 STATIC void
225 xfs_cil_prepare_item(
226         struct xlog             *log,
227         struct xfs_log_vec      *lv,
228         struct xfs_log_vec      *old_lv,
229         int                     *diff_len,
230         int                     *diff_iovecs)
231 {
232         /* Account for the new LV being passed in */
233         if (lv->lv_buf_len != XFS_LOG_VEC_ORDERED) {
234                 *diff_len += lv->lv_bytes;
235                 *diff_iovecs += lv->lv_niovecs;
236         }
237 
238         /*
239          * If there is no old LV, this is the first time we've seen the item in
240          * this CIL context and so we need to pin it. If we are replacing the
241          * old_lv, then remove the space it accounts for and make it the shadow
242          * buffer for later freeing. In both cases we are now switching to the
243          * shadow buffer, so update the the pointer to it appropriately.
244          */
245         if (!old_lv) {
246                 if (lv->lv_item->li_ops->iop_pin)
247                         lv->lv_item->li_ops->iop_pin(lv->lv_item);
248                 lv->lv_item->li_lv_shadow = NULL;
249         } else if (old_lv != lv) {
250                 ASSERT(lv->lv_buf_len != XFS_LOG_VEC_ORDERED);
251 
252                 *diff_len -= old_lv->lv_bytes;
253                 *diff_iovecs -= old_lv->lv_niovecs;
254                 lv->lv_item->li_lv_shadow = old_lv;
255         }
256 
257         /* attach new log vector to log item */
258         lv->lv_item->li_lv = lv;
259 
260         /*
261          * If this is the first time the item is being committed to the
262          * CIL, store the sequence number on the log item so we can
263          * tell in future commits whether this is the first checkpoint
264          * the item is being committed into.
265          */
266         if (!lv->lv_item->li_seq)
267                 lv->lv_item->li_seq = log->l_cilp->xc_ctx->sequence;
268 }
269 
270 /*
271  * Format log item into a flat buffers
272  *
273  * For delayed logging, we need to hold a formatted buffer containing all the
274  * changes on the log item. This enables us to relog the item in memory and
275  * write it out asynchronously without needing to relock the object that was
276  * modified at the time it gets written into the iclog.
277  *
278  * This function takes the prepared log vectors attached to each log item, and
279  * formats the changes into the log vector buffer. The buffer it uses is
280  * dependent on the current state of the vector in the CIL - the shadow lv is
281  * guaranteed to be large enough for the current modification, but we will only
282  * use that if we can't reuse the existing lv. If we can't reuse the existing
283  * lv, then simple swap it out for the shadow lv. We don't free it - that is
284  * done lazily either by th enext modification or the freeing of the log item.
285  *
286  * We don't set up region headers during this process; we simply copy the
287  * regions into the flat buffer. We can do this because we still have to do a
288  * formatting step to write the regions into the iclog buffer.  Writing the
289  * ophdrs during the iclog write means that we can support splitting large
290  * regions across iclog boundares without needing a change in the format of the
291  * item/region encapsulation.
292  *
293  * Hence what we need to do now is change the rewrite the vector array to point
294  * to the copied region inside the buffer we just allocated. This allows us to
295  * format the regions into the iclog as though they are being formatted
296  * directly out of the objects themselves.
297  */
298 static void
299 xlog_cil_insert_format_items(
300         struct xlog             *log,
301         struct xfs_trans        *tp,
302         int                     *diff_len,
303         int                     *diff_iovecs)
304 {
305         struct xfs_log_item     *lip;
306 
307 
308         /* Bail out if we didn't find a log item.  */
309         if (list_empty(&tp->t_items)) {
310                 ASSERT(0);
311                 return;
312         }
313 
314         list_for_each_entry(lip, &tp->t_items, li_trans) {
315                 struct xfs_log_vec *lv;
316                 struct xfs_log_vec *old_lv = NULL;
317                 struct xfs_log_vec *shadow;
318                 bool    ordered = false;
319 
320                 /* Skip items which aren't dirty in this transaction. */
321                 if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
322                         continue;
323 
324                 /*
325                  * The formatting size information is already attached to
326                  * the shadow lv on the log item.
327                  */
328                 shadow = lip->li_lv_shadow;
329                 if (shadow->lv_buf_len == XFS_LOG_VEC_ORDERED)
330                         ordered = true;
331 
332                 /* Skip items that do not have any vectors for writing */
333                 if (!shadow->lv_niovecs && !ordered)
334                         continue;
335 
336                 /* compare to existing item size */
337                 old_lv = lip->li_lv;
338                 if (lip->li_lv && shadow->lv_size <= lip->li_lv->lv_size) {
339                         /* same or smaller, optimise common overwrite case */
340                         lv = lip->li_lv;
341                         lv->lv_next = NULL;
342 
343                         if (ordered)
344                                 goto insert;
345 
346                         /*
347                          * set the item up as though it is a new insertion so
348                          * that the space reservation accounting is correct.
349                          */
350                         *diff_iovecs -= lv->lv_niovecs;
351                         *diff_len -= lv->lv_bytes;
352 
353                         /* Ensure the lv is set up according to ->iop_size */
354                         lv->lv_niovecs = shadow->lv_niovecs;
355 
356                         /* reset the lv buffer information for new formatting */
357                         lv->lv_buf_len = 0;
358                         lv->lv_bytes = 0;
359                         lv->lv_buf = (char *)lv +
360                                         xlog_cil_iovec_space(lv->lv_niovecs);
361                 } else {
362                         /* switch to shadow buffer! */
363                         lv = shadow;
364                         lv->lv_item = lip;
365                         if (ordered) {
366                                 /* track as an ordered logvec */
367                                 ASSERT(lip->li_lv == NULL);
368                                 goto insert;
369                         }
370                 }
371 
372                 ASSERT(IS_ALIGNED((unsigned long)lv->lv_buf, sizeof(uint64_t)));
373                 lip->li_ops->iop_format(lip, lv);
374 insert:
375                 xfs_cil_prepare_item(log, lv, old_lv, diff_len, diff_iovecs);
376         }
377 }
378 
379 /*
380  * Insert the log items into the CIL and calculate the difference in space
381  * consumed by the item. Add the space to the checkpoint ticket and calculate
382  * if the change requires additional log metadata. If it does, take that space
383  * as well. Remove the amount of space we added to the checkpoint ticket from
384  * the current transaction ticket so that the accounting works out correctly.
385  */
386 static void
387 xlog_cil_insert_items(
388         struct xlog             *log,
389         struct xfs_trans        *tp)
390 {
391         struct xfs_cil          *cil = log->l_cilp;
392         struct xfs_cil_ctx      *ctx = cil->xc_ctx;
393         struct xfs_log_item     *lip;
394         int                     len = 0;
395         int                     diff_iovecs = 0;
396         int                     iclog_space;
397         int                     iovhdr_res = 0, split_res = 0, ctx_res = 0;
398 
399         ASSERT(tp);
400 
401         /*
402          * We can do this safely because the context can't checkpoint until we
403          * are done so it doesn't matter exactly how we update the CIL.
404          */
405         xlog_cil_insert_format_items(log, tp, &len, &diff_iovecs);
406 
407         spin_lock(&cil->xc_cil_lock);
408 
409         /* account for space used by new iovec headers  */
410         iovhdr_res = diff_iovecs * sizeof(xlog_op_header_t);
411         len += iovhdr_res;
412         ctx->nvecs += diff_iovecs;
413 
414         /* attach the transaction to the CIL if it has any busy extents */
415         if (!list_empty(&tp->t_busy))
416                 list_splice_init(&tp->t_busy, &ctx->busy_extents);
417 
418         /*
419          * Now transfer enough transaction reservation to the context ticket
420          * for the checkpoint. The context ticket is special - the unit
421          * reservation has to grow as well as the current reservation as we
422          * steal from tickets so we can correctly determine the space used
423          * during the transaction commit.
424          */
425         if (ctx->ticket->t_curr_res == 0) {
426                 ctx_res = ctx->ticket->t_unit_res;
427                 ctx->ticket->t_curr_res = ctx_res;
428                 tp->t_ticket->t_curr_res -= ctx_res;
429         }
430 
431         /* do we need space for more log record headers? */
432         iclog_space = log->l_iclog_size - log->l_iclog_hsize;
433         if (len > 0 && (ctx->space_used / iclog_space !=
434                                 (ctx->space_used + len) / iclog_space)) {
435                 split_res = (len + iclog_space - 1) / iclog_space;
436                 /* need to take into account split region headers, too */
437                 split_res *= log->l_iclog_hsize + sizeof(struct xlog_op_header);
438                 ctx->ticket->t_unit_res += split_res;
439                 ctx->ticket->t_curr_res += split_res;
440                 tp->t_ticket->t_curr_res -= split_res;
441                 ASSERT(tp->t_ticket->t_curr_res >= len);
442         }
443         tp->t_ticket->t_curr_res -= len;
444         ctx->space_used += len;
445 
446         /*
447          * If we've overrun the reservation, dump the tx details before we move
448          * the log items. Shutdown is imminent...
449          */
450         if (WARN_ON(tp->t_ticket->t_curr_res < 0)) {
451                 xfs_warn(log->l_mp, "Transaction log reservation overrun:");
452                 xfs_warn(log->l_mp,
453                          "  log items: %d bytes (iov hdrs: %d bytes)",
454                          len, iovhdr_res);
455                 xfs_warn(log->l_mp, "  split region headers: %d bytes",
456                          split_res);
457                 xfs_warn(log->l_mp, "  ctx ticket: %d bytes", ctx_res);
458                 xlog_print_trans(tp);
459         }
460 
461         /*
462          * Now (re-)position everything modified at the tail of the CIL.
463          * We do this here so we only need to take the CIL lock once during
464          * the transaction commit.
465          */
466         list_for_each_entry(lip, &tp->t_items, li_trans) {
467 
468                 /* Skip items which aren't dirty in this transaction. */
469                 if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
470                         continue;
471 
472                 /*
473                  * Only move the item if it isn't already at the tail. This is
474                  * to prevent a transient list_empty() state when reinserting
475                  * an item that is already the only item in the CIL.
476                  */
477                 if (!list_is_last(&lip->li_cil, &cil->xc_cil))
478                         list_move_tail(&lip->li_cil, &cil->xc_cil);
479         }
480 
481         spin_unlock(&cil->xc_cil_lock);
482 
483         if (tp->t_ticket->t_curr_res < 0)
484                 xfs_force_shutdown(log->l_mp, SHUTDOWN_LOG_IO_ERROR);
485 }
486 
487 static void
488 xlog_cil_free_logvec(
489         struct xfs_log_vec      *log_vector)
490 {
491         struct xfs_log_vec      *lv;
492 
493         for (lv = log_vector; lv; ) {
494                 struct xfs_log_vec *next = lv->lv_next;
495                 kmem_free(lv);
496                 lv = next;
497         }
498 }
499 
500 static void
501 xlog_discard_endio_work(
502         struct work_struct      *work)
503 {
504         struct xfs_cil_ctx      *ctx =
505                 container_of(work, struct xfs_cil_ctx, discard_endio_work);
506         struct xfs_mount        *mp = ctx->cil->xc_log->l_mp;
507 
508         xfs_extent_busy_clear(mp, &ctx->busy_extents, false);
509         kmem_free(ctx);
510 }
511 
512 /*
513  * Queue up the actual completion to a thread to avoid IRQ-safe locking for
514  * pagb_lock.  Note that we need a unbounded workqueue, otherwise we might
515  * get the execution delayed up to 30 seconds for weird reasons.
516  */
517 static void
518 xlog_discard_endio(
519         struct bio              *bio)
520 {
521         struct xfs_cil_ctx      *ctx = bio->bi_private;
522 
523         INIT_WORK(&ctx->discard_endio_work, xlog_discard_endio_work);
524         queue_work(xfs_discard_wq, &ctx->discard_endio_work);
525         bio_put(bio);
526 }
527 
528 static void
529 xlog_discard_busy_extents(
530         struct xfs_mount        *mp,
531         struct xfs_cil_ctx      *ctx)
532 {
533         struct list_head        *list = &ctx->busy_extents;
534         struct xfs_extent_busy  *busyp;
535         struct bio              *bio = NULL;
536         struct blk_plug         plug;
537         int                     error = 0;
538 
539         ASSERT(mp->m_flags & XFS_MOUNT_DISCARD);
540 
541         blk_start_plug(&plug);
542         list_for_each_entry(busyp, list, list) {
543                 trace_xfs_discard_extent(mp, busyp->agno, busyp->bno,
544                                          busyp->length);
545 
546                 error = __blkdev_issue_discard(mp->m_ddev_targp->bt_bdev,
547                                 XFS_AGB_TO_DADDR(mp, busyp->agno, busyp->bno),
548                                 XFS_FSB_TO_BB(mp, busyp->length),
549                                 GFP_NOFS, 0, &bio);
550                 if (error && error != -EOPNOTSUPP) {
551                         xfs_info(mp,
552          "discard failed for extent [0x%llx,%u], error %d",
553                                  (unsigned long long)busyp->bno,
554                                  busyp->length,
555                                  error);
556                         break;
557                 }
558         }
559 
560         if (bio) {
561                 bio->bi_private = ctx;
562                 bio->bi_end_io = xlog_discard_endio;
563                 submit_bio(bio);
564         } else {
565                 xlog_discard_endio_work(&ctx->discard_endio_work);
566         }
567         blk_finish_plug(&plug);
568 }
569 
570 /*
571  * Mark all items committed and clear busy extents. We free the log vector
572  * chains in a separate pass so that we unpin the log items as quickly as
573  * possible.
574  */
575 static void
576 xlog_cil_committed(
577         struct xfs_cil_ctx      *ctx,
578         bool                    abort)
579 {
580         struct xfs_mount        *mp = ctx->cil->xc_log->l_mp;
581 
582         /*
583          * If the I/O failed, we're aborting the commit and already shutdown.
584          * Wake any commit waiters before aborting the log items so we don't
585          * block async log pushers on callbacks. Async log pushers explicitly do
586          * not wait on log force completion because they may be holding locks
587          * required to unpin items.
588          */
589         if (abort) {
590                 spin_lock(&ctx->cil->xc_push_lock);
591                 wake_up_all(&ctx->cil->xc_commit_wait);
592                 spin_unlock(&ctx->cil->xc_push_lock);
593         }
594 
595         xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
596                                         ctx->start_lsn, abort);
597 
598         xfs_extent_busy_sort(&ctx->busy_extents);
599         xfs_extent_busy_clear(mp, &ctx->busy_extents,
600                              (mp->m_flags & XFS_MOUNT_DISCARD) && !abort);
601 
602         spin_lock(&ctx->cil->xc_push_lock);
603         list_del(&ctx->committing);
604         spin_unlock(&ctx->cil->xc_push_lock);
605 
606         xlog_cil_free_logvec(ctx->lv_chain);
607 
608         if (!list_empty(&ctx->busy_extents))
609                 xlog_discard_busy_extents(mp, ctx);
610         else
611                 kmem_free(ctx);
612 }
613 
614 void
615 xlog_cil_process_committed(
616         struct list_head        *list,
617         bool                    aborted)
618 {
619         struct xfs_cil_ctx      *ctx;
620 
621         while ((ctx = list_first_entry_or_null(list,
622                         struct xfs_cil_ctx, iclog_entry))) {
623                 list_del(&ctx->iclog_entry);
624                 xlog_cil_committed(ctx, aborted);
625         }
626 }
627 
628 /*
629  * Push the Committed Item List to the log. If @push_seq flag is zero, then it
630  * is a background flush and so we can chose to ignore it. Otherwise, if the
631  * current sequence is the same as @push_seq we need to do a flush. If
632  * @push_seq is less than the current sequence, then it has already been
633  * flushed and we don't need to do anything - the caller will wait for it to
634  * complete if necessary.
635  *
636  * @push_seq is a value rather than a flag because that allows us to do an
637  * unlocked check of the sequence number for a match. Hence we can allows log
638  * forces to run racily and not issue pushes for the same sequence twice. If we
639  * get a race between multiple pushes for the same sequence they will block on
640  * the first one and then abort, hence avoiding needless pushes.
641  */
642 STATIC int
643 xlog_cil_push(
644         struct xlog             *log)
645 {
646         struct xfs_cil          *cil = log->l_cilp;
647         struct xfs_log_vec      *lv;
648         struct xfs_cil_ctx      *ctx;
649         struct xfs_cil_ctx      *new_ctx;
650         struct xlog_in_core     *commit_iclog;
651         struct xlog_ticket      *tic;
652         int                     num_iovecs;
653         int                     error = 0;
654         struct xfs_trans_header thdr;
655         struct xfs_log_iovec    lhdr;
656         struct xfs_log_vec      lvhdr = { NULL };
657         xfs_lsn_t               commit_lsn;
658         xfs_lsn_t               push_seq;
659 
660         if (!cil)
661                 return 0;
662 
663         new_ctx = kmem_zalloc(sizeof(*new_ctx), KM_NOFS);
664         new_ctx->ticket = xlog_cil_ticket_alloc(log);
665 
666         down_write(&cil->xc_ctx_lock);
667         ctx = cil->xc_ctx;
668 
669         spin_lock(&cil->xc_push_lock);
670         push_seq = cil->xc_push_seq;
671         ASSERT(push_seq <= ctx->sequence);
672 
673         /*
674          * Check if we've anything to push. If there is nothing, then we don't
675          * move on to a new sequence number and so we have to be able to push
676          * this sequence again later.
677          */
678         if (list_empty(&cil->xc_cil)) {
679                 cil->xc_push_seq = 0;
680                 spin_unlock(&cil->xc_push_lock);
681                 goto out_skip;
682         }
683 
684 
685         /* check for a previously pushed sequence */
686         if (push_seq < cil->xc_ctx->sequence) {
687                 spin_unlock(&cil->xc_push_lock);
688                 goto out_skip;
689         }
690 
691         /*
692          * We are now going to push this context, so add it to the committing
693          * list before we do anything else. This ensures that anyone waiting on
694          * this push can easily detect the difference between a "push in
695          * progress" and "CIL is empty, nothing to do".
696          *
697          * IOWs, a wait loop can now check for:
698          *      the current sequence not being found on the committing list;
699          *      an empty CIL; and
700          *      an unchanged sequence number
701          * to detect a push that had nothing to do and therefore does not need
702          * waiting on. If the CIL is not empty, we get put on the committing
703          * list before emptying the CIL and bumping the sequence number. Hence
704          * an empty CIL and an unchanged sequence number means we jumped out
705          * above after doing nothing.
706          *
707          * Hence the waiter will either find the commit sequence on the
708          * committing list or the sequence number will be unchanged and the CIL
709          * still dirty. In that latter case, the push has not yet started, and
710          * so the waiter will have to continue trying to check the CIL
711          * committing list until it is found. In extreme cases of delay, the
712          * sequence may fully commit between the attempts the wait makes to wait
713          * on the commit sequence.
714          */
715         list_add(&ctx->committing, &cil->xc_committing);
716         spin_unlock(&cil->xc_push_lock);
717 
718         /*
719          * pull all the log vectors off the items in the CIL, and
720          * remove the items from the CIL. We don't need the CIL lock
721          * here because it's only needed on the transaction commit
722          * side which is currently locked out by the flush lock.
723          */
724         lv = NULL;
725         num_iovecs = 0;
726         while (!list_empty(&cil->xc_cil)) {
727                 struct xfs_log_item     *item;
728 
729                 item = list_first_entry(&cil->xc_cil,
730                                         struct xfs_log_item, li_cil);
731                 list_del_init(&item->li_cil);
732                 if (!ctx->lv_chain)
733                         ctx->lv_chain = item->li_lv;
734                 else
735                         lv->lv_next = item->li_lv;
736                 lv = item->li_lv;
737                 item->li_lv = NULL;
738                 num_iovecs += lv->lv_niovecs;
739         }
740 
741         /*
742          * initialise the new context and attach it to the CIL. Then attach
743          * the current context to the CIL committing lsit so it can be found
744          * during log forces to extract the commit lsn of the sequence that
745          * needs to be forced.
746          */
747         INIT_LIST_HEAD(&new_ctx->committing);
748         INIT_LIST_HEAD(&new_ctx->busy_extents);
749         new_ctx->sequence = ctx->sequence + 1;
750         new_ctx->cil = cil;
751         cil->xc_ctx = new_ctx;
752 
753         /*
754          * The switch is now done, so we can drop the context lock and move out
755          * of a shared context. We can't just go straight to the commit record,
756          * though - we need to synchronise with previous and future commits so
757          * that the commit records are correctly ordered in the log to ensure
758          * that we process items during log IO completion in the correct order.
759          *
760          * For example, if we get an EFI in one checkpoint and the EFD in the
761          * next (e.g. due to log forces), we do not want the checkpoint with
762          * the EFD to be committed before the checkpoint with the EFI.  Hence
763          * we must strictly order the commit records of the checkpoints so
764          * that: a) the checkpoint callbacks are attached to the iclogs in the
765          * correct order; and b) the checkpoints are replayed in correct order
766          * in log recovery.
767          *
768          * Hence we need to add this context to the committing context list so
769          * that higher sequences will wait for us to write out a commit record
770          * before they do.
771          *
772          * xfs_log_force_lsn requires us to mirror the new sequence into the cil
773          * structure atomically with the addition of this sequence to the
774          * committing list. This also ensures that we can do unlocked checks
775          * against the current sequence in log forces without risking
776          * deferencing a freed context pointer.
777          */
778         spin_lock(&cil->xc_push_lock);
779         cil->xc_current_sequence = new_ctx->sequence;
780         spin_unlock(&cil->xc_push_lock);
781         up_write(&cil->xc_ctx_lock);
782 
783         /*
784          * Build a checkpoint transaction header and write it to the log to
785          * begin the transaction. We need to account for the space used by the
786          * transaction header here as it is not accounted for in xlog_write().
787          *
788          * The LSN we need to pass to the log items on transaction commit is
789          * the LSN reported by the first log vector write. If we use the commit
790          * record lsn then we can move the tail beyond the grant write head.
791          */
792         tic = ctx->ticket;
793         thdr.th_magic = XFS_TRANS_HEADER_MAGIC;
794         thdr.th_type = XFS_TRANS_CHECKPOINT;
795         thdr.th_tid = tic->t_tid;
796         thdr.th_num_items = num_iovecs;
797         lhdr.i_addr = &thdr;
798         lhdr.i_len = sizeof(xfs_trans_header_t);
799         lhdr.i_type = XLOG_REG_TYPE_TRANSHDR;
800         tic->t_curr_res -= lhdr.i_len + sizeof(xlog_op_header_t);
801 
802         lvhdr.lv_niovecs = 1;
803         lvhdr.lv_iovecp = &lhdr;
804         lvhdr.lv_next = ctx->lv_chain;
805 
806         error = xlog_write(log, &lvhdr, tic, &ctx->start_lsn, NULL, 0);
807         if (error)
808                 goto out_abort_free_ticket;
809 
810         /*
811          * now that we've written the checkpoint into the log, strictly
812          * order the commit records so replay will get them in the right order.
813          */
814 restart:
815         spin_lock(&cil->xc_push_lock);
816         list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
817                 /*
818                  * Avoid getting stuck in this loop because we were woken by the
819                  * shutdown, but then went back to sleep once already in the
820                  * shutdown state.
821                  */
822                 if (XLOG_FORCED_SHUTDOWN(log)) {
823                         spin_unlock(&cil->xc_push_lock);
824                         goto out_abort_free_ticket;
825                 }
826 
827                 /*
828                  * Higher sequences will wait for this one so skip them.
829                  * Don't wait for our own sequence, either.
830                  */
831                 if (new_ctx->sequence >= ctx->sequence)
832                         continue;
833                 if (!new_ctx->commit_lsn) {
834                         /*
835                          * It is still being pushed! Wait for the push to
836                          * complete, then start again from the beginning.
837                          */
838                         xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
839                         goto restart;
840                 }
841         }
842         spin_unlock(&cil->xc_push_lock);
843 
844         /* xfs_log_done always frees the ticket on error. */
845         commit_lsn = xfs_log_done(log->l_mp, tic, &commit_iclog, false);
846         if (commit_lsn == -1)
847                 goto out_abort;
848 
849         spin_lock(&commit_iclog->ic_callback_lock);
850         if (commit_iclog->ic_state == XLOG_STATE_IOERROR) {
851                 spin_unlock(&commit_iclog->ic_callback_lock);
852                 goto out_abort;
853         }
854         ASSERT_ALWAYS(commit_iclog->ic_state == XLOG_STATE_ACTIVE ||
855                       commit_iclog->ic_state == XLOG_STATE_WANT_SYNC);
856         list_add_tail(&ctx->iclog_entry, &commit_iclog->ic_callbacks);
857         spin_unlock(&commit_iclog->ic_callback_lock);
858 
859         /*
860          * now the checkpoint commit is complete and we've attached the
861          * callbacks to the iclog we can assign the commit LSN to the context
862          * and wake up anyone who is waiting for the commit to complete.
863          */
864         spin_lock(&cil->xc_push_lock);
865         ctx->commit_lsn = commit_lsn;
866         wake_up_all(&cil->xc_commit_wait);
867         spin_unlock(&cil->xc_push_lock);
868 
869         /* release the hounds! */
870         return xfs_log_release_iclog(log->l_mp, commit_iclog);
871 
872 out_skip:
873         up_write(&cil->xc_ctx_lock);
874         xfs_log_ticket_put(new_ctx->ticket);
875         kmem_free(new_ctx);
876         return 0;
877 
878 out_abort_free_ticket:
879         xfs_log_ticket_put(tic);
880 out_abort:
881         xlog_cil_committed(ctx, true);
882         return -EIO;
883 }
884 
885 static void
886 xlog_cil_push_work(
887         struct work_struct      *work)
888 {
889         struct xfs_cil          *cil = container_of(work, struct xfs_cil,
890                                                         xc_push_work);
891         xlog_cil_push(cil->xc_log);
892 }
893 
894 /*
895  * We need to push CIL every so often so we don't cache more than we can fit in
896  * the log. The limit really is that a checkpoint can't be more than half the
897  * log (the current checkpoint is not allowed to overwrite the previous
898  * checkpoint), but commit latency and memory usage limit this to a smaller
899  * size.
900  */
901 static void
902 xlog_cil_push_background(
903         struct xlog     *log)
904 {
905         struct xfs_cil  *cil = log->l_cilp;
906 
907         /*
908          * The cil won't be empty because we are called while holding the
909          * context lock so whatever we added to the CIL will still be there
910          */
911         ASSERT(!list_empty(&cil->xc_cil));
912 
913         /*
914          * don't do a background push if we haven't used up all the
915          * space available yet.
916          */
917         if (cil->xc_ctx->space_used < XLOG_CIL_SPACE_LIMIT(log))
918                 return;
919 
920         spin_lock(&cil->xc_push_lock);
921         if (cil->xc_push_seq < cil->xc_current_sequence) {
922                 cil->xc_push_seq = cil->xc_current_sequence;
923                 queue_work(log->l_mp->m_cil_workqueue, &cil->xc_push_work);
924         }
925         spin_unlock(&cil->xc_push_lock);
926 
927 }
928 
929 /*
930  * xlog_cil_push_now() is used to trigger an immediate CIL push to the sequence
931  * number that is passed. When it returns, the work will be queued for
932  * @push_seq, but it won't be completed. The caller is expected to do any
933  * waiting for push_seq to complete if it is required.
934  */
935 static void
936 xlog_cil_push_now(
937         struct xlog     *log,
938         xfs_lsn_t       push_seq)
939 {
940         struct xfs_cil  *cil = log->l_cilp;
941 
942         if (!cil)
943                 return;
944 
945         ASSERT(push_seq && push_seq <= cil->xc_current_sequence);
946 
947         /* start on any pending background push to minimise wait time on it */
948         flush_work(&cil->xc_push_work);
949 
950         /*
951          * If the CIL is empty or we've already pushed the sequence then
952          * there's no work we need to do.
953          */
954         spin_lock(&cil->xc_push_lock);
955         if (list_empty(&cil->xc_cil) || push_seq <= cil->xc_push_seq) {
956                 spin_unlock(&cil->xc_push_lock);
957                 return;
958         }
959 
960         cil->xc_push_seq = push_seq;
961         queue_work(log->l_mp->m_cil_workqueue, &cil->xc_push_work);
962         spin_unlock(&cil->xc_push_lock);
963 }
964 
965 bool
966 xlog_cil_empty(
967         struct xlog     *log)
968 {
969         struct xfs_cil  *cil = log->l_cilp;
970         bool            empty = false;
971 
972         spin_lock(&cil->xc_push_lock);
973         if (list_empty(&cil->xc_cil))
974                 empty = true;
975         spin_unlock(&cil->xc_push_lock);
976         return empty;
977 }
978 
979 /*
980  * Commit a transaction with the given vector to the Committed Item List.
981  *
982  * To do this, we need to format the item, pin it in memory if required and
983  * account for the space used by the transaction. Once we have done that we
984  * need to release the unused reservation for the transaction, attach the
985  * transaction to the checkpoint context so we carry the busy extents through
986  * to checkpoint completion, and then unlock all the items in the transaction.
987  *
988  * Called with the context lock already held in read mode to lock out
989  * background commit, returns without it held once background commits are
990  * allowed again.
991  */
992 void
993 xfs_log_commit_cil(
994         struct xfs_mount        *mp,
995         struct xfs_trans        *tp,
996         xfs_lsn_t               *commit_lsn,
997         bool                    regrant)
998 {
999         struct xlog             *log = mp->m_log;
1000         struct xfs_cil          *cil = log->l_cilp;
1001         struct xfs_log_item     *lip, *next;
1002         xfs_lsn_t               xc_commit_lsn;
1003 
1004         /*
1005          * Do all necessary memory allocation before we lock the CIL.
1006          * This ensures the allocation does not deadlock with a CIL
1007          * push in memory reclaim (e.g. from kswapd).
1008          */
1009         xlog_cil_alloc_shadow_bufs(log, tp);
1010 
1011         /* lock out background commit */
1012         down_read(&cil->xc_ctx_lock);
1013 
1014         xlog_cil_insert_items(log, tp);
1015 
1016         xc_commit_lsn = cil->xc_ctx->sequence;
1017         if (commit_lsn)
1018                 *commit_lsn = xc_commit_lsn;
1019 
1020         xfs_log_done(mp, tp->t_ticket, NULL, regrant);
1021         tp->t_ticket = NULL;
1022         xfs_trans_unreserve_and_mod_sb(tp);
1023 
1024         /*
1025          * Once all the items of the transaction have been copied to the CIL,
1026          * the items can be unlocked and possibly freed.
1027          *
1028          * This needs to be done before we drop the CIL context lock because we
1029          * have to update state in the log items and unlock them before they go
1030          * to disk. If we don't, then the CIL checkpoint can race with us and
1031          * we can run checkpoint completion before we've updated and unlocked
1032          * the log items. This affects (at least) processing of stale buffers,
1033          * inodes and EFIs.
1034          */
1035         trace_xfs_trans_commit_items(tp, _RET_IP_);
1036         list_for_each_entry_safe(lip, next, &tp->t_items, li_trans) {
1037                 xfs_trans_del_item(lip);
1038                 if (lip->li_ops->iop_committing)
1039                         lip->li_ops->iop_committing(lip, xc_commit_lsn);
1040         }
1041         xlog_cil_push_background(log);
1042 
1043         up_read(&cil->xc_ctx_lock);
1044 }
1045 
1046 /*
1047  * Conditionally push the CIL based on the sequence passed in.
1048  *
1049  * We only need to push if we haven't already pushed the sequence
1050  * number given. Hence the only time we will trigger a push here is
1051  * if the push sequence is the same as the current context.
1052  *
1053  * We return the current commit lsn to allow the callers to determine if a
1054  * iclog flush is necessary following this call.
1055  */
1056 xfs_lsn_t
1057 xlog_cil_force_lsn(
1058         struct xlog     *log,
1059         xfs_lsn_t       sequence)
1060 {
1061         struct xfs_cil          *cil = log->l_cilp;
1062         struct xfs_cil_ctx      *ctx;
1063         xfs_lsn_t               commit_lsn = NULLCOMMITLSN;
1064 
1065         ASSERT(sequence <= cil->xc_current_sequence);
1066 
1067         /*
1068          * check to see if we need to force out the current context.
1069          * xlog_cil_push() handles racing pushes for the same sequence,
1070          * so no need to deal with it here.
1071          */
1072 restart:
1073         xlog_cil_push_now(log, sequence);
1074 
1075         /*
1076          * See if we can find a previous sequence still committing.
1077          * We need to wait for all previous sequence commits to complete
1078          * before allowing the force of push_seq to go ahead. Hence block
1079          * on commits for those as well.
1080          */
1081         spin_lock(&cil->xc_push_lock);
1082         list_for_each_entry(ctx, &cil->xc_committing, committing) {
1083                 /*
1084                  * Avoid getting stuck in this loop because we were woken by the
1085                  * shutdown, but then went back to sleep once already in the
1086                  * shutdown state.
1087                  */
1088                 if (XLOG_FORCED_SHUTDOWN(log))
1089                         goto out_shutdown;
1090                 if (ctx->sequence > sequence)
1091                         continue;
1092                 if (!ctx->commit_lsn) {
1093                         /*
1094                          * It is still being pushed! Wait for the push to
1095                          * complete, then start again from the beginning.
1096                          */
1097                         xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
1098                         goto restart;
1099                 }
1100                 if (ctx->sequence != sequence)
1101                         continue;
1102                 /* found it! */
1103                 commit_lsn = ctx->commit_lsn;
1104         }
1105 
1106         /*
1107          * The call to xlog_cil_push_now() executes the push in the background.
1108          * Hence by the time we have got here it our sequence may not have been
1109          * pushed yet. This is true if the current sequence still matches the
1110          * push sequence after the above wait loop and the CIL still contains
1111          * dirty objects. This is guaranteed by the push code first adding the
1112          * context to the committing list before emptying the CIL.
1113          *
1114          * Hence if we don't find the context in the committing list and the
1115          * current sequence number is unchanged then the CIL contents are
1116          * significant.  If the CIL is empty, if means there was nothing to push
1117          * and that means there is nothing to wait for. If the CIL is not empty,
1118          * it means we haven't yet started the push, because if it had started
1119          * we would have found the context on the committing list.
1120          */
1121         if (sequence == cil->xc_current_sequence &&
1122             !list_empty(&cil->xc_cil)) {
1123                 spin_unlock(&cil->xc_push_lock);
1124                 goto restart;
1125         }
1126 
1127         spin_unlock(&cil->xc_push_lock);
1128         return commit_lsn;
1129 
1130         /*
1131          * We detected a shutdown in progress. We need to trigger the log force
1132          * to pass through it's iclog state machine error handling, even though
1133          * we are already in a shutdown state. Hence we can't return
1134          * NULLCOMMITLSN here as that has special meaning to log forces (i.e.
1135          * LSN is already stable), so we return a zero LSN instead.
1136          */
1137 out_shutdown:
1138         spin_unlock(&cil->xc_push_lock);
1139         return 0;
1140 }
1141 
1142 /*
1143  * Check if the current log item was first committed in this sequence.
1144  * We can't rely on just the log item being in the CIL, we have to check
1145  * the recorded commit sequence number.
1146  *
1147  * Note: for this to be used in a non-racy manner, it has to be called with
1148  * CIL flushing locked out. As a result, it should only be used during the
1149  * transaction commit process when deciding what to format into the item.
1150  */
1151 bool
1152 xfs_log_item_in_current_chkpt(
1153         struct xfs_log_item *lip)
1154 {
1155         struct xfs_cil_ctx *ctx;
1156 
1157         if (list_empty(&lip->li_cil))
1158                 return false;
1159 
1160         ctx = lip->li_mountp->m_log->l_cilp->xc_ctx;
1161 
1162         /*
1163          * li_seq is written on the first commit of a log item to record the
1164          * first checkpoint it is written to. Hence if it is different to the
1165          * current sequence, we're in a new checkpoint.
1166          */
1167         if (XFS_LSN_CMP(lip->li_seq, ctx->sequence) != 0)
1168                 return false;
1169         return true;
1170 }
1171 
1172 /*
1173  * Perform initial CIL structure initialisation.
1174  */
1175 int
1176 xlog_cil_init(
1177         struct xlog     *log)
1178 {
1179         struct xfs_cil  *cil;
1180         struct xfs_cil_ctx *ctx;
1181 
1182         cil = kmem_zalloc(sizeof(*cil), KM_MAYFAIL);
1183         if (!cil)
1184                 return -ENOMEM;
1185 
1186         ctx = kmem_zalloc(sizeof(*ctx), KM_MAYFAIL);
1187         if (!ctx) {
1188                 kmem_free(cil);
1189                 return -ENOMEM;
1190         }
1191 
1192         INIT_WORK(&cil->xc_push_work, xlog_cil_push_work);
1193         INIT_LIST_HEAD(&cil->xc_cil);
1194         INIT_LIST_HEAD(&cil->xc_committing);
1195         spin_lock_init(&cil->xc_cil_lock);
1196         spin_lock_init(&cil->xc_push_lock);
1197         init_rwsem(&cil->xc_ctx_lock);
1198         init_waitqueue_head(&cil->xc_commit_wait);
1199 
1200         INIT_LIST_HEAD(&ctx->committing);
1201         INIT_LIST_HEAD(&ctx->busy_extents);
1202         ctx->sequence = 1;
1203         ctx->cil = cil;
1204         cil->xc_ctx = ctx;
1205         cil->xc_current_sequence = ctx->sequence;
1206 
1207         cil->xc_log = log;
1208         log->l_cilp = cil;
1209         return 0;
1210 }
1211 
1212 void
1213 xlog_cil_destroy(
1214         struct xlog     *log)
1215 {
1216         if (log->l_cilp->xc_ctx) {
1217                 if (log->l_cilp->xc_ctx->ticket)
1218                         xfs_log_ticket_put(log->l_cilp->xc_ctx->ticket);
1219                 kmem_free(log->l_cilp->xc_ctx);
1220         }
1221 
1222         ASSERT(list_empty(&log->l_cilp->xc_cil));
1223         kmem_free(log->l_cilp);
1224 }
1225 
1226 

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