fs/ext4/mmp.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/fs.h>
   3 #include <linux/random.h>
   4 #include <linux/buffer_head.h>
   5 #include <linux/utsname.h>
   6 #include <linux/kthread.h>
   7
   8 #include "ext4.h"
   9
  10 /* Checksumming functions */
  11 static __le32 ext4_mmp_csum(struct super_block *sb, struct mmp_struct *mmp)
  12 {
  13         struct ext4_sb_info *sbi = EXT4_SB(sb);
  14         int offset = offsetof(struct mmp_struct, mmp_checksum);
  15         __u32 csum;
  16
  17         csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);
  18
  19         return cpu_to_le32(csum);
  20 }
  21
  22 static int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
  23 {
  24         if (!ext4_has_metadata_csum(sb))
  25                 return 1;
  26
  27         return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
  28 }
  29
  30 static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
  31 {
  32         if (!ext4_has_metadata_csum(sb))
  33                 return;
  34
  35         mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
  36 }
  37
  38 /*
  39  * Write the MMP block using REQ_SYNC to try to get the block on-disk
  40  * faster.
  41  */
  42 static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
  43 {
  44         struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);
  45
  46         /*
  47          * We protect against freezing so that we don't create dirty buffers
  48          * on frozen filesystem.
  49          */
  50         sb_start_write(sb);
  51         ext4_mmp_csum_set(sb, mmp);
  52         lock_buffer(bh);
  53         bh->b_end_io = end_buffer_write_sync;
  54         get_bh(bh);
  55         submit_bh(REQ_OP_WRITE | REQ_SYNC | REQ_META | REQ_PRIO, bh);
  56         wait_on_buffer(bh);
  57         sb_end_write(sb);
  58         if (unlikely(!buffer_uptodate(bh)))
  59                 return -EIO;
  60
  61         return 0;
  62 }
  63
  64 /*
  65  * Read the MMP block. It _must_ be read from disk and hence we clear the
  66  * uptodate flag on the buffer.
  67  */
  68 static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
  69                           ext4_fsblk_t mmp_block)
  70 {
  71         struct mmp_struct *mmp;
  72         int ret;
  73
  74         if (*bh)
  75                 clear_buffer_uptodate(*bh);
  76
  77         /* This would be sb_bread(sb, mmp_block), except we need to be sure
  78          * that the MD RAID device cache has been bypassed, and that the read
  79          * is not blocked in the elevator. */
  80         if (!*bh) {
  81                 *bh = sb_getblk(sb, mmp_block);
  82                 if (!*bh) {
  83                         ret = -ENOMEM;
  84                         goto warn_exit;
  85                 }
  86         }
  87
  88         lock_buffer(*bh);
  89         ret = ext4_read_bh(*bh, REQ_META | REQ_PRIO, NULL);
  90         if (ret)
  91                 goto warn_exit;
  92
  93         mmp = (struct mmp_struct *)((*bh)->b_data);
  94         if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
  95                 ret = -EFSCORRUPTED;
  96                 goto warn_exit;
  97         }
  98         if (!ext4_mmp_csum_verify(sb, mmp)) {
  99                 ret = -EFSBADCRC;
 100                 goto warn_exit;
 101         }
 102         return 0;
 103 warn_exit:
 104         brelse(*bh);
 105         *bh = NULL;
 106         ext4_warning(sb, "Error %d while reading MMP block %llu",
 107                      ret, mmp_block);
 108         return ret;
 109 }
 110
 111 /*
 112  * Dump as much information as possible to help the admin.
 113  */
 114 void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
 115                     const char *function, unsigned int line, const char *msg)
 116 {
 117         __ext4_warning(sb, function, line, "%s", msg);
 118         __ext4_warning(sb, function, line,
 119                        "MMP failure info: last update time: %llu, last update node: %.*s, last update device: %.*s",
 120                        (unsigned long long)le64_to_cpu(mmp->mmp_time),
 121                        (int)sizeof(mmp->mmp_nodename), mmp->mmp_nodename,
 122                        (int)sizeof(mmp->mmp_bdevname), mmp->mmp_bdevname);
 123 }
 124
 125 /*
 126  * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
 127  */
 128 static int kmmpd(void *data)
 129 {
 130         struct super_block *sb = data;
 131         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
 132         struct buffer_head *bh = EXT4_SB(sb)->s_mmp_bh;
 133         struct mmp_struct *mmp;
 134         ext4_fsblk_t mmp_block;
 135         u32 seq = 0;
 136         unsigned long failed_writes = 0;
 137         int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
 138         unsigned mmp_check_interval;
 139         unsigned long last_update_time;
 140         unsigned long diff;
 141         int retval = 0;
 142
 143         mmp_block = le64_to_cpu(es->s_mmp_block);
 144         mmp = (struct mmp_struct *)(bh->b_data);
 145         mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
 146         /*
 147          * Start with the higher mmp_check_interval and reduce it if
 148          * the MMP block is being updated on time.
 149          */
 150         mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
 151                                  EXT4_MMP_MIN_CHECK_INTERVAL);
 152         mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
 153
 154         memcpy(mmp->mmp_nodename, init_utsname()->nodename,
 155                sizeof(mmp->mmp_nodename));
 156
 157         while (!kthread_should_stop() && !sb_rdonly(sb)) {
 158                 if (!ext4_has_feature_mmp(sb)) {
 159                         ext4_warning(sb, "kmmpd being stopped since MMP feature"
 160                                      " has been disabled.");
 161                         goto wait_to_exit;
 162                 }
 163                 if (++seq > EXT4_MMP_SEQ_MAX)
 164                         seq = 1;
 165
 166                 mmp->mmp_seq = cpu_to_le32(seq);
 167                 mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
 168                 last_update_time = jiffies;
 169
 170                 retval = write_mmp_block(sb, bh);
 171                 /*
 172                  * Don't spew too many error messages. Print one every
 173                  * (s_mmp_update_interval * 60) seconds.
 174                  */
 175                 if (retval) {
 176                         if ((failed_writes % 60) == 0) {
 177                                 ext4_error_err(sb, -retval,
 178                                                "Error writing to MMP block");
 179                         }
 180                         failed_writes++;
 181                 }
 182
 183                 diff = jiffies - last_update_time;
 184                 if (diff < mmp_update_interval * HZ)
 185                         schedule_timeout_interruptible(mmp_update_interval *
 186                                                        HZ - diff);
 187
 188                 /*
 189                  * We need to make sure that more than mmp_check_interval
 190                  * seconds have not passed since writing. If that has happened
 191                  * we need to check if the MMP block is as we left it.
 192                  */
 193                 diff = jiffies - last_update_time;
 194                 if (diff > mmp_check_interval * HZ) {
 195                         struct buffer_head *bh_check = NULL;
 196                         struct mmp_struct *mmp_check;
 197
 198                         retval = read_mmp_block(sb, &bh_check, mmp_block);
 199                         if (retval) {
 200                                 ext4_error_err(sb, -retval,
 201                                                "error reading MMP data: %d",
 202                                                retval);
 203                                 goto wait_to_exit;
 204                         }
 205
 206                         mmp_check = (struct mmp_struct *)(bh_check->b_data);
 207                         if (mmp->mmp_seq != mmp_check->mmp_seq ||
 208                             memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
 209                                    sizeof(mmp->mmp_nodename))) {
 210                                 dump_mmp_msg(sb, mmp_check,
 211                                              "Error while updating MMP info. "
 212                                              "The filesystem seems to have been"
 213                                              " multiply mounted.");
 214                                 ext4_error_err(sb, EBUSY, "abort");
 215                                 put_bh(bh_check);
 216                                 retval = -EBUSY;
 217                                 goto wait_to_exit;
 218                         }
 219                         put_bh(bh_check);
 220                 }
 221
 222                  /*
 223                  * Adjust the mmp_check_interval depending on how much time
 224                  * it took for the MMP block to be written.
 225                  */
 226                 mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
 227                                              EXT4_MMP_MAX_CHECK_INTERVAL),
 228                                          EXT4_MMP_MIN_CHECK_INTERVAL);
 229                 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
 230         }
 231
 232         /*
 233          * Unmount seems to be clean.
 234          */
 235         mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
 236         mmp->mmp_time = cpu_to_le64(ktime_get_real_seconds());
 237
 238         retval = write_mmp_block(sb, bh);
 239
 240 wait_to_exit:
 241         while (!kthread_should_stop()) {
 242                 set_current_state(TASK_INTERRUPTIBLE);
 243                 if (!kthread_should_stop())
 244                         schedule();
 245         }
 246         set_current_state(TASK_RUNNING);
 247         return retval;
 248 }
 249
 250 void ext4_stop_mmpd(struct ext4_sb_info *sbi)
 251 {
 252         if (sbi->s_mmp_tsk) {
 253                 kthread_stop(sbi->s_mmp_tsk);
 254                 brelse(sbi->s_mmp_bh);
 255                 sbi->s_mmp_tsk = NULL;
 256         }
 257 }
 258
 259 /*
 260  * Get a random new sequence number but make sure it is not greater than
 261  * EXT4_MMP_SEQ_MAX.
 262  */
 263 static unsigned int mmp_new_seq(void)
 264 {
 265         u32 new_seq;
 266
 267         do {
 268                 new_seq = prandom_u32();
 269         } while (new_seq > EXT4_MMP_SEQ_MAX);
 270
 271         return new_seq;
 272 }
 273
 274 /*
 275  * Protect the filesystem from being mounted more than once.
 276  */
 277 int ext4_multi_mount_protect(struct super_block *sb,
 278                                     ext4_fsblk_t mmp_block)
 279 {
 280         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
 281         struct buffer_head *bh = NULL;
 282         struct mmp_struct *mmp = NULL;
 283         u32 seq;
 284         unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
 285         unsigned int wait_time = 0;
 286         int retval;
 287
 288         if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
 289             mmp_block >= ext4_blocks_count(es)) {
 290                 ext4_warning(sb, "Invalid MMP block in superblock");
 291                 goto failed;
 292         }
 293
 294         retval = read_mmp_block(sb, &bh, mmp_block);
 295         if (retval)
 296                 goto failed;
 297
 298         mmp = (struct mmp_struct *)(bh->b_data);
 299
 300         if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
 301                 mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
 302
 303         /*
 304          * If check_interval in MMP block is larger, use that instead of
 305          * update_interval from the superblock.
 306          */
 307         if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
 308                 mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
 309
 310         seq = le32_to_cpu(mmp->mmp_seq);
 311         if (seq == EXT4_MMP_SEQ_CLEAN)
 312                 goto skip;
 313
 314         if (seq == EXT4_MMP_SEQ_FSCK) {
 315                 dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
 316                 goto failed;
 317         }
 318
 319         wait_time = min(mmp_check_interval * 2 + 1,
 320                         mmp_check_interval + 60);
 321
 322         /* Print MMP interval if more than 20 secs. */
 323         if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
 324                 ext4_warning(sb, "MMP interval %u higher than expected, please"
 325                              " wait.\n", wait_time * 2);
 326
 327         if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
 328                 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
 329                 goto failed;
 330         }
 331
 332         retval = read_mmp_block(sb, &bh, mmp_block);
 333         if (retval)
 334                 goto failed;
 335         mmp = (struct mmp_struct *)(bh->b_data);
 336         if (seq != le32_to_cpu(mmp->mmp_seq)) {
 337                 dump_mmp_msg(sb, mmp,
 338                              "Device is already active on another node.");
 339                 goto failed;
 340         }
 341
 342 skip:
 343         /*
 344          * write a new random sequence number.
 345          */
 346         seq = mmp_new_seq();
 347         mmp->mmp_seq = cpu_to_le32(seq);
 348
 349         retval = write_mmp_block(sb, bh);
 350         if (retval)
 351                 goto failed;
 352
 353         /*
 354          * wait for MMP interval and check mmp_seq.
 355          */
 356         if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
 357                 ext4_warning(sb, "MMP startup interrupted, failing mount");
 358                 goto failed;
 359         }
 360
 361         retval = read_mmp_block(sb, &bh, mmp_block);
 362         if (retval)
 363                 goto failed;
 364         mmp = (struct mmp_struct *)(bh->b_data);
 365         if (seq != le32_to_cpu(mmp->mmp_seq)) {
 366                 dump_mmp_msg(sb, mmp,
 367                              "Device is already active on another node.");
 368                 goto failed;
 369         }
 370
 371         EXT4_SB(sb)->s_mmp_bh = bh;
 372
 373         BUILD_BUG_ON(sizeof(mmp->mmp_bdevname) < BDEVNAME_SIZE);
 374         snprintf(mmp->mmp_bdevname, sizeof(mmp->mmp_bdevname),
 375                  "%pg", bh->b_bdev);
 376
 377         /*
 378          * Start a kernel thread to update the MMP block periodically.
 379          */
 380         EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, sb, "kmmpd-%.*s",
 381                                              (int)sizeof(mmp->mmp_bdevname),
 382                                              mmp->mmp_bdevname);
 383         if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
 384                 EXT4_SB(sb)->s_mmp_tsk = NULL;
 385                 ext4_warning(sb, "Unable to create kmmpd thread for %s.",
 386                              sb->s_id);
 387                 goto failed;
 388         }
 389
 390         return 0;
 391
 392 failed:
 393         brelse(bh);
 394         return 1;
 395 }