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         mark_buffer_dirty(bh);
  53         lock_buffer(bh);
  54         bh->b_end_io = end_buffer_write_sync;
  55         get_bh(bh);
  56         submit_bh(REQ_OP_WRITE, REQ_SYNC | REQ_META | REQ_PRIO, bh);
  57         wait_on_buffer(bh);
  58         sb_end_write(sb);
  59         if (unlikely(!buffer_uptodate(bh)))
  60                 return 1;
  61
  62         return 0;
  63 }
  64
  65 /*
  66  * Read the MMP block. It _must_ be read from disk and hence we clear the
  67  * uptodate flag on the buffer.
  68  */
  69 static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
  70                           ext4_fsblk_t mmp_block)
  71 {
  72         struct mmp_struct *mmp;
  73         int ret;
  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                         ret = -ENOMEM;
  85                         goto warn_exit;
  86                 }
  87         }
  88
  89         get_bh(*bh);
  90         lock_buffer(*bh);
  91         (*bh)->b_end_io = end_buffer_read_sync;
  92         submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO, *bh);
  93         wait_on_buffer(*bh);
  94         if (!buffer_uptodate(*bh)) {
  95                 ret = -EIO;
  96                 goto warn_exit;
  97         }
  98         mmp = (struct mmp_struct *)((*bh)->b_data);
  99         if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC) {
 100                 ret = -EFSCORRUPTED;
 101                 goto warn_exit;
 102         }
 103         if (!ext4_mmp_csum_verify(sb, mmp)) {
 104                 ret = -EFSBADCRC;
 105                 goto warn_exit;
 106         }
 107         return 0;
 108 warn_exit:
 109         brelse(*bh);
 110         *bh = NULL;
 111         ext4_warning(sb, "Error %d while reading MMP block %llu",
 112                      ret, mmp_block);
 113         return ret;
 114 }
 115
 116 /*
 117  * Dump as much information as possible to help the admin.
 118  */
 119 void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
 120                     const char *function, unsigned int line, const char *msg)
 121 {
 122         __ext4_warning(sb, function, line, "%s", msg);
 123         __ext4_warning(sb, function, line,
 124                        "MMP failure info: last update time: %llu, last update "
 125                        "node: %s, last update device: %s",
 126                        (long long unsigned int) le64_to_cpu(mmp->mmp_time),
 127                        mmp->mmp_nodename, mmp->mmp_bdevname);
 128 }
 129
 130 /*
 131  * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
 132  */
 133 static int kmmpd(void *data)
 134 {
 135         struct super_block *sb = ((struct mmpd_data *) data)->sb;
 136         struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
 137         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
 138         struct mmp_struct *mmp;
 139         ext4_fsblk_t mmp_block;
 140         u32 seq = 0;
 141         unsigned long failed_writes = 0;
 142         int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
 143         unsigned mmp_check_interval;
 144         unsigned long last_update_time;
 145         unsigned long diff;
 146         int retval;
 147
 148         mmp_block = le64_to_cpu(es->s_mmp_block);
 149         mmp = (struct mmp_struct *)(bh->b_data);
 150         mmp->mmp_time = cpu_to_le64(get_seconds());
 151         /*
 152          * Start with the higher mmp_check_interval and reduce it if
 153          * the MMP block is being updated on time.
 154          */
 155         mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
 156                                  EXT4_MMP_MIN_CHECK_INTERVAL);
 157         mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
 158         bdevname(bh->b_bdev, mmp->mmp_bdevname);
 159
 160         memcpy(mmp->mmp_nodename, init_utsname()->nodename,
 161                sizeof(mmp->mmp_nodename));
 162
 163         while (!kthread_should_stop()) {
 164                 if (++seq > EXT4_MMP_SEQ_MAX)
 165                         seq = 1;
 166
 167                 mmp->mmp_seq = cpu_to_le32(seq);
 168                 mmp->mmp_time = cpu_to_le64(get_seconds());
 169                 last_update_time = jiffies;
 170
 171                 retval = write_mmp_block(sb, bh);
 172                 /*
 173                  * Don't spew too many error messages. Print one every
 174                  * (s_mmp_update_interval * 60) seconds.
 175                  */
 176                 if (retval) {
 177                         if ((failed_writes % 60) == 0)
 178                                 ext4_error(sb, "Error writing to MMP block");
 179                         failed_writes++;
 180                 }
 181
 182                 if (!(le32_to_cpu(es->s_feature_incompat) &
 183                     EXT4_FEATURE_INCOMPAT_MMP)) {
 184                         ext4_warning(sb, "kmmpd being stopped since MMP feature"
 185                                      " has been disabled.");
 186                         goto exit_thread;
 187                 }
 188
 189                 if (sb_rdonly(sb)) {
 190                         ext4_warning(sb, "kmmpd being stopped since filesystem "
 191                                      "has been remounted as readonly.");
 192                         goto exit_thread;
 193                 }
 194
 195                 diff = jiffies - last_update_time;
 196                 if (diff < mmp_update_interval * HZ)
 197                         schedule_timeout_interruptible(mmp_update_interval *
 198                                                        HZ - diff);
 199
 200                 /*
 201                  * We need to make sure that more than mmp_check_interval
 202                  * seconds have not passed since writing. If that has happened
 203                  * we need to check if the MMP block is as we left it.
 204                  */
 205                 diff = jiffies - last_update_time;
 206                 if (diff > mmp_check_interval * HZ) {
 207                         struct buffer_head *bh_check = NULL;
 208                         struct mmp_struct *mmp_check;
 209
 210                         retval = read_mmp_block(sb, &bh_check, mmp_block);
 211                         if (retval) {
 212                                 ext4_error(sb, "error reading MMP data: %d",
 213                                            retval);
 214                                 goto exit_thread;
 215                         }
 216
 217                         mmp_check = (struct mmp_struct *)(bh_check->b_data);
 218                         if (mmp->mmp_seq != mmp_check->mmp_seq ||
 219                             memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
 220                                    sizeof(mmp->mmp_nodename))) {
 221                                 dump_mmp_msg(sb, mmp_check,
 222                                              "Error while updating MMP info. "
 223                                              "The filesystem seems to have been"
 224                                              " multiply mounted.");
 225                                 ext4_error(sb, "abort");
 226                                 put_bh(bh_check);
 227                                 retval = -EBUSY;
 228                                 goto exit_thread;
 229                         }
 230                         put_bh(bh_check);
 231                 }
 232
 233                  /*
 234                  * Adjust the mmp_check_interval depending on how much time
 235                  * it took for the MMP block to be written.
 236                  */
 237                 mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
 238                                              EXT4_MMP_MAX_CHECK_INTERVAL),
 239                                          EXT4_MMP_MIN_CHECK_INTERVAL);
 240                 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
 241         }
 242
 243         /*
 244          * Unmount seems to be clean.
 245          */
 246         mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
 247         mmp->mmp_time = cpu_to_le64(get_seconds());
 248
 249         retval = write_mmp_block(sb, bh);
 250
 251 exit_thread:
 252         EXT4_SB(sb)->s_mmp_tsk = NULL;
 253         kfree(data);
 254         brelse(bh);
 255         return retval;
 256 }
 257
 258 /*
 259  * Get a random new sequence number but make sure it is not greater than
 260  * EXT4_MMP_SEQ_MAX.
 261  */
 262 static unsigned int mmp_new_seq(void)
 263 {
 264         u32 new_seq;
 265
 266         do {
 267                 new_seq = prandom_u32();
 268         } while (new_seq > EXT4_MMP_SEQ_MAX);
 269
 270         return new_seq;
 271 }
 272
 273 /*
 274  * Protect the filesystem from being mounted more than once.
 275  */
 276 int ext4_multi_mount_protect(struct super_block *sb,
 277                                     ext4_fsblk_t mmp_block)
 278 {
 279         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
 280         struct buffer_head *bh = NULL;
 281         struct mmp_struct *mmp = NULL;
 282         struct mmpd_data *mmpd_data;
 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         mmpd_data = kmalloc(sizeof(*mmpd_data), GFP_KERNEL);
 372         if (!mmpd_data) {
 373                 ext4_warning(sb, "not enough memory for mmpd_data");
 374                 goto failed;
 375         }
 376         mmpd_data->sb = sb;
 377         mmpd_data->bh = bh;
 378
 379         /*
 380          * Start a kernel thread to update the MMP block periodically.
 381          */
 382         EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%s",
 383                                              bdevname(bh->b_bdev,
 384                                                       mmp->mmp_bdevname));
 385         if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
 386                 EXT4_SB(sb)->s_mmp_tsk = NULL;
 387                 kfree(mmpd_data);
 388                 ext4_warning(sb, "Unable to create kmmpd thread for %s.",
 389                              sb->s_id);
 390                 goto failed;
 391         }
 392
 393         return 0;
 394
 395 failed:
 396         brelse(bh);
 397         return 1;
 398 }
 399
 400