fs/ext4/mmp.c

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