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TOMOYO Linux Cross Reference
Linux/fs/ext4/mmp.c

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  1 #include <linux/fs.h>
  2 #include <linux/random.h>
  3 #include <linux/buffer_head.h>
  4 #include <linux/utsname.h>
  5 #include <linux/kthread.h>
  6 
  7 #include "ext4.h"
  8 
  9 /* Checksumming functions */
 10 static __le32 ext4_mmp_csum(struct super_block *sb, struct mmp_struct *mmp)
 11 {
 12         struct ext4_sb_info *sbi = EXT4_SB(sb);
 13         int offset = offsetof(struct mmp_struct, mmp_checksum);
 14         __u32 csum;
 15 
 16         csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);
 17 
 18         return cpu_to_le32(csum);
 19 }
 20 
 21 int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
 22 {
 23         if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
 24                                        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
 25                 return 1;
 26 
 27         return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
 28 }
 29 
 30 void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
 31 {
 32         if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
 33                                        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
 34                 return;
 35 
 36         mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
 37 }
 38 
 39 /*
 40  * Write the MMP block using WRITE_SYNC to try to get the block on-disk
 41  * faster.
 42  */
 43 static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
 44 {
 45         struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);
 46 
 47         /*
 48          * We protect against freezing so that we don't create dirty buffers
 49          * on frozen filesystem.
 50          */
 51         sb_start_write(sb);
 52         ext4_mmp_csum_set(sb, mmp);
 53         mark_buffer_dirty(bh);
 54         lock_buffer(bh);
 55         bh->b_end_io = end_buffer_write_sync;
 56         get_bh(bh);
 57         submit_bh(WRITE_SYNC | REQ_META | REQ_PRIO, bh);
 58         wait_on_buffer(bh);
 59         sb_end_write(sb);
 60         if (unlikely(!buffer_uptodate(bh)))
 61                 return 1;
 62 
 63         return 0;
 64 }
 65 
 66 /*
 67  * Read the MMP block. It _must_ be read from disk and hence we clear the
 68  * uptodate flag on the buffer.
 69  */
 70 static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
 71                           ext4_fsblk_t mmp_block)
 72 {
 73         struct mmp_struct *mmp;
 74 
 75         if (*bh)
 76                 clear_buffer_uptodate(*bh);
 77 
 78         /* This would be sb_bread(sb, mmp_block), except we need to be sure
 79          * that the MD RAID device cache has been bypassed, and that the read
 80          * is not blocked in the elevator. */
 81         if (!*bh)
 82                 *bh = sb_getblk(sb, mmp_block);
 83         if (!*bh)
 84                 return -ENOMEM;
 85         if (*bh) {
 86                 get_bh(*bh);
 87                 lock_buffer(*bh);
 88                 (*bh)->b_end_io = end_buffer_read_sync;
 89                 submit_bh(READ_SYNC | REQ_META | REQ_PRIO, *bh);
 90                 wait_on_buffer(*bh);
 91                 if (!buffer_uptodate(*bh)) {
 92                         brelse(*bh);
 93                         *bh = NULL;
 94                 }
 95         }
 96         if (unlikely(!*bh)) {
 97                 ext4_warning(sb, "Error while reading MMP block %llu",
 98                              mmp_block);
 99                 return -EIO;
100         }
101 
102         mmp = (struct mmp_struct *)((*bh)->b_data);
103         if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC ||
104             !ext4_mmp_csum_verify(sb, mmp))
105                 return -EINVAL;
106 
107         return 0;
108 }
109 
110 /*
111  * Dump as much information as possible to help the admin.
112  */
113 void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
114                     const char *function, unsigned int line, const char *msg)
115 {
116         __ext4_warning(sb, function, line, msg);
117         __ext4_warning(sb, function, line,
118                        "MMP failure info: last update time: %llu, last update "
119                        "node: %s, last update device: %s\n",
120                        (long long unsigned int) le64_to_cpu(mmp->mmp_time),
121                        mmp->mmp_nodename, mmp->mmp_bdevname);
122 }
123 
124 /*
125  * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
126  */
127 static int kmmpd(void *data)
128 {
129         struct super_block *sb = ((struct mmpd_data *) data)->sb;
130         struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
131         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
132         struct mmp_struct *mmp;
133         ext4_fsblk_t mmp_block;
134         u32 seq = 0;
135         unsigned long failed_writes = 0;
136         int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
137         unsigned mmp_check_interval;
138         unsigned long last_update_time;
139         unsigned long diff;
140         int retval;
141 
142         mmp_block = le64_to_cpu(es->s_mmp_block);
143         mmp = (struct mmp_struct *)(bh->b_data);
144         mmp->mmp_time = cpu_to_le64(get_seconds());
145         /*
146          * Start with the higher mmp_check_interval and reduce it if
147          * the MMP block is being updated on time.
148          */
149         mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
150                                  EXT4_MMP_MIN_CHECK_INTERVAL);
151         mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
152         bdevname(bh->b_bdev, mmp->mmp_bdevname);
153 
154         memcpy(mmp->mmp_nodename, init_utsname()->nodename,
155                sizeof(mmp->mmp_nodename));
156 
157         while (!kthread_should_stop()) {
158                 if (++seq > EXT4_MMP_SEQ_MAX)
159                         seq = 1;
160 
161                 mmp->mmp_seq = cpu_to_le32(seq);
162                 mmp->mmp_time = cpu_to_le64(get_seconds());
163                 last_update_time = jiffies;
164 
165                 retval = write_mmp_block(sb, bh);
166                 /*
167                  * Don't spew too many error messages. Print one every
168                  * (s_mmp_update_interval * 60) seconds.
169                  */
170                 if (retval) {
171                         if ((failed_writes % 60) == 0)
172                                 ext4_error(sb, "Error writing to MMP block");
173                         failed_writes++;
174                 }
175 
176                 if (!(le32_to_cpu(es->s_feature_incompat) &
177                     EXT4_FEATURE_INCOMPAT_MMP)) {
178                         ext4_warning(sb, "kmmpd being stopped since MMP feature"
179                                      " has been disabled.");
180                         EXT4_SB(sb)->s_mmp_tsk = NULL;
181                         goto failed;
182                 }
183 
184                 if (sb->s_flags & MS_RDONLY) {
185                         ext4_warning(sb, "kmmpd being stopped since filesystem "
186                                      "has been remounted as readonly.");
187                         EXT4_SB(sb)->s_mmp_tsk = NULL;
188                         goto failed;
189                 }
190 
191                 diff = jiffies - last_update_time;
192                 if (diff < mmp_update_interval * HZ)
193                         schedule_timeout_interruptible(mmp_update_interval *
194                                                        HZ - diff);
195 
196                 /*
197                  * We need to make sure that more than mmp_check_interval
198                  * seconds have not passed since writing. If that has happened
199                  * we need to check if the MMP block is as we left it.
200                  */
201                 diff = jiffies - last_update_time;
202                 if (diff > mmp_check_interval * HZ) {
203                         struct buffer_head *bh_check = NULL;
204                         struct mmp_struct *mmp_check;
205 
206                         retval = read_mmp_block(sb, &bh_check, mmp_block);
207                         if (retval) {
208                                 ext4_error(sb, "error reading MMP data: %d",
209                                            retval);
210 
211                                 EXT4_SB(sb)->s_mmp_tsk = NULL;
212                                 goto failed;
213                         }
214 
215                         mmp_check = (struct mmp_struct *)(bh_check->b_data);
216                         if (mmp->mmp_seq != mmp_check->mmp_seq ||
217                             memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
218                                    sizeof(mmp->mmp_nodename))) {
219                                 dump_mmp_msg(sb, mmp_check,
220                                              "Error while updating MMP info. "
221                                              "The filesystem seems to have been"
222                                              " multiply mounted.");
223                                 ext4_error(sb, "abort");
224                                 goto failed;
225                         }
226                         put_bh(bh_check);
227                 }
228 
229                  /*
230                  * Adjust the mmp_check_interval depending on how much time
231                  * it took for the MMP block to be written.
232                  */
233                 mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
234                                              EXT4_MMP_MAX_CHECK_INTERVAL),
235                                          EXT4_MMP_MIN_CHECK_INTERVAL);
236                 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
237         }
238 
239         /*
240          * Unmount seems to be clean.
241          */
242         mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
243         mmp->mmp_time = cpu_to_le64(get_seconds());
244 
245         retval = write_mmp_block(sb, bh);
246 
247 failed:
248         kfree(data);
249         brelse(bh);
250         return retval;
251 }
252 
253 /*
254  * Get a random new sequence number but make sure it is not greater than
255  * EXT4_MMP_SEQ_MAX.
256  */
257 static unsigned int mmp_new_seq(void)
258 {
259         u32 new_seq;
260 
261         do {
262                 get_random_bytes(&new_seq, sizeof(u32));
263         } while (new_seq > EXT4_MMP_SEQ_MAX);
264 
265         return new_seq;
266 }
267 
268 /*
269  * Protect the filesystem from being mounted more than once.
270  */
271 int ext4_multi_mount_protect(struct super_block *sb,
272                                     ext4_fsblk_t mmp_block)
273 {
274         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
275         struct buffer_head *bh = NULL;
276         struct mmp_struct *mmp = NULL;
277         struct mmpd_data *mmpd_data;
278         u32 seq;
279         unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
280         unsigned int wait_time = 0;
281         int retval;
282 
283         if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
284             mmp_block >= ext4_blocks_count(es)) {
285                 ext4_warning(sb, "Invalid MMP block in superblock");
286                 goto failed;
287         }
288 
289         retval = read_mmp_block(sb, &bh, mmp_block);
290         if (retval)
291                 goto failed;
292 
293         mmp = (struct mmp_struct *)(bh->b_data);
294 
295         if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
296                 mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
297 
298         /*
299          * If check_interval in MMP block is larger, use that instead of
300          * update_interval from the superblock.
301          */
302         if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
303                 mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
304 
305         seq = le32_to_cpu(mmp->mmp_seq);
306         if (seq == EXT4_MMP_SEQ_CLEAN)
307                 goto skip;
308 
309         if (seq == EXT4_MMP_SEQ_FSCK) {
310                 dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
311                 goto failed;
312         }
313 
314         wait_time = min(mmp_check_interval * 2 + 1,
315                         mmp_check_interval + 60);
316 
317         /* Print MMP interval if more than 20 secs. */
318         if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
319                 ext4_warning(sb, "MMP interval %u higher than expected, please"
320                              " wait.\n", wait_time * 2);
321 
322         if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
323                 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
324                 goto failed;
325         }
326 
327         retval = read_mmp_block(sb, &bh, mmp_block);
328         if (retval)
329                 goto failed;
330         mmp = (struct mmp_struct *)(bh->b_data);
331         if (seq != le32_to_cpu(mmp->mmp_seq)) {
332                 dump_mmp_msg(sb, mmp,
333                              "Device is already active on another node.");
334                 goto failed;
335         }
336 
337 skip:
338         /*
339          * write a new random sequence number.
340          */
341         seq = mmp_new_seq();
342         mmp->mmp_seq = cpu_to_le32(seq);
343 
344         retval = write_mmp_block(sb, bh);
345         if (retval)
346                 goto failed;
347 
348         /*
349          * wait for MMP interval and check mmp_seq.
350          */
351         if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
352                 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
353                 goto failed;
354         }
355 
356         retval = read_mmp_block(sb, &bh, mmp_block);
357         if (retval)
358                 goto failed;
359         mmp = (struct mmp_struct *)(bh->b_data);
360         if (seq != le32_to_cpu(mmp->mmp_seq)) {
361                 dump_mmp_msg(sb, mmp,
362                              "Device is already active on another node.");
363                 goto failed;
364         }
365 
366         mmpd_data = kmalloc(sizeof(struct mmpd_data), GFP_KERNEL);
367         if (!mmpd_data) {
368                 ext4_warning(sb, "not enough memory for mmpd_data");
369                 goto failed;
370         }
371         mmpd_data->sb = sb;
372         mmpd_data->bh = bh;
373 
374         /*
375          * Start a kernel thread to update the MMP block periodically.
376          */
377         EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%s",
378                                              bdevname(bh->b_bdev,
379                                                       mmp->mmp_bdevname));
380         if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
381                 EXT4_SB(sb)->s_mmp_tsk = NULL;
382                 kfree(mmpd_data);
383                 ext4_warning(sb, "Unable to create kmmpd thread for %s.",
384                              sb->s_id);
385                 goto failed;
386         }
387 
388         return 0;
389 
390 failed:
391         brelse(bh);
392         return 1;
393 }
394 
395 
396 

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