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 /* 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 static int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
  22 {
  23         if (!ext4_has_metadata_csum(sb))
  24                 return 1;
  25
  26         return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
  27 }
  28
  29 static void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
  30 {
  31         if (!ext4_has_metadata_csum(sb))
  32                 return;
  33
  34         mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
  35 }
  36
  37 /*
  38  * Write the MMP block using WRITE_SYNC to try to get the block on-disk
  39  * faster.
  40  */
  41 static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
  42 {
  43         struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);
  44
  45         /*
  46          * We protect against freezing so that we don't create dirty buffers
  47          * on frozen filesystem.
  48          */
  49         sb_start_write(sb);
  50         ext4_mmp_csum_set(sb, mmp);
  51         mark_buffer_dirty(bh);
  52         lock_buffer(bh);
  53         bh->b_end_io = end_buffer_write_sync;
  54         get_bh(bh);
  55         submit_bh(WRITE_SYNC | REQ_META | REQ_PRIO, bh);
  56         wait_on_buffer(bh);
  57         sb_end_write(sb);
  58         if (unlikely(!buffer_uptodate(bh)))
  59                 return 1;
  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
  73         if (*bh)
  74                 clear_buffer_uptodate(*bh);
  75
  76         /* This would be sb_bread(sb, mmp_block), except we need to be sure
  77          * that the MD RAID device cache has been bypassed, and that the read
  78          * is not blocked in the elevator. */
  79         if (!*bh)
  80                 *bh = sb_getblk(sb, mmp_block);
  81         if (!*bh)
  82                 return -ENOMEM;
  83         if (*bh) {
  84                 get_bh(*bh);
  85                 lock_buffer(*bh);
  86                 (*bh)->b_end_io = end_buffer_read_sync;
  87                 submit_bh(READ_SYNC | REQ_META | REQ_PRIO, *bh);
  88                 wait_on_buffer(*bh);
  89                 if (!buffer_uptodate(*bh)) {
  90                         brelse(*bh);
  91                         *bh = NULL;
  92                 }
  93         }
  94         if (unlikely(!*bh)) {
  95                 ext4_warning(sb, "Error while reading MMP block %llu",
  96                              mmp_block);
  97                 return -EIO;
  98         }
  99
 100         mmp = (struct mmp_struct *)((*bh)->b_data);
 101         if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC ||
 102             !ext4_mmp_csum_verify(sb, mmp))
 103                 return -EINVAL;
 104
 105         return 0;
 106 }
 107
 108 /*
 109  * Dump as much information as possible to help the admin.
 110  */
 111 void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
 112                     const char *function, unsigned int line, const char *msg)
 113 {
 114         __ext4_warning(sb, function, line, msg);
 115         __ext4_warning(sb, function, line,
 116                        "MMP failure info: last update time: %llu, last update "
 117                        "node: %s, last update device: %s\n",
 118                        (long long unsigned int) le64_to_cpu(mmp->mmp_time),
 119                        mmp->mmp_nodename, mmp->mmp_bdevname);
 120 }
 121
 122 /*
 123  * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
 124  */
 125 static int kmmpd(void *data)
 126 {
 127         struct super_block *sb = ((struct mmpd_data *) data)->sb;
 128         struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
 129         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
 130         struct mmp_struct *mmp;
 131         ext4_fsblk_t mmp_block;
 132         u32 seq = 0;
 133         unsigned long failed_writes = 0;
 134         int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
 135         unsigned mmp_check_interval;
 136         unsigned long last_update_time;
 137         unsigned long diff;
 138         int retval;
 139
 140         mmp_block = le64_to_cpu(es->s_mmp_block);
 141         mmp = (struct mmp_struct *)(bh->b_data);
 142         mmp->mmp_time = cpu_to_le64(get_seconds());
 143         /*
 144          * Start with the higher mmp_check_interval and reduce it if
 145          * the MMP block is being updated on time.
 146          */
 147         mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
 148                                  EXT4_MMP_MIN_CHECK_INTERVAL);
 149         mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
 150         bdevname(bh->b_bdev, mmp->mmp_bdevname);
 151
 152         memcpy(mmp->mmp_nodename, init_utsname()->nodename,
 153                sizeof(mmp->mmp_nodename));
 154
 155         while (!kthread_should_stop()) {
 156                 if (++seq > EXT4_MMP_SEQ_MAX)
 157                         seq = 1;
 158
 159                 mmp->mmp_seq = cpu_to_le32(seq);
 160                 mmp->mmp_time = cpu_to_le64(get_seconds());
 161                 last_update_time = jiffies;
 162
 163                 retval = write_mmp_block(sb, bh);
 164                 /*
 165                  * Don't spew too many error messages. Print one every
 166                  * (s_mmp_update_interval * 60) seconds.
 167                  */
 168                 if (retval) {
 169                         if ((failed_writes % 60) == 0)
 170                                 ext4_error(sb, "Error writing to MMP block");
 171                         failed_writes++;
 172                 }
 173
 174                 if (!(le32_to_cpu(es->s_feature_incompat) &
 175                     EXT4_FEATURE_INCOMPAT_MMP)) {
 176                         ext4_warning(sb, "kmmpd being stopped since MMP feature"
 177                                      " has been disabled.");
 178                         EXT4_SB(sb)->s_mmp_tsk = NULL;
 179                         goto failed;
 180                 }
 181
 182                 if (sb->s_flags & MS_RDONLY) {
 183                         ext4_warning(sb, "kmmpd being stopped since filesystem "
 184                                      "has been remounted as readonly.");
 185                         EXT4_SB(sb)->s_mmp_tsk = NULL;
 186                         goto failed;
 187                 }
 188
 189                 diff = jiffies - last_update_time;
 190                 if (diff < mmp_update_interval * HZ)
 191                         schedule_timeout_interruptible(mmp_update_interval *
 192                                                        HZ - diff);
 193
 194                 /*
 195                  * We need to make sure that more than mmp_check_interval
 196                  * seconds have not passed since writing. If that has happened
 197                  * we need to check if the MMP block is as we left it.
 198                  */
 199                 diff = jiffies - last_update_time;
 200                 if (diff > mmp_check_interval * HZ) {
 201                         struct buffer_head *bh_check = NULL;
 202                         struct mmp_struct *mmp_check;
 203
 204                         retval = read_mmp_block(sb, &bh_check, mmp_block);
 205                         if (retval) {
 206                                 ext4_error(sb, "error reading MMP data: %d",
 207                                            retval);
 208
 209                                 EXT4_SB(sb)->s_mmp_tsk = NULL;
 210                                 goto failed;
 211                         }
 212
 213                         mmp_check = (struct mmp_struct *)(bh_check->b_data);
 214                         if (mmp->mmp_seq != mmp_check->mmp_seq ||
 215                             memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
 216                                    sizeof(mmp->mmp_nodename))) {
 217                                 dump_mmp_msg(sb, mmp_check,
 218                                              "Error while updating MMP info. "
 219                                              "The filesystem seems to have been"
 220                                              " multiply mounted.");
 221                                 ext4_error(sb, "abort");
 222                                 goto failed;
 223                         }
 224                         put_bh(bh_check);
 225                 }
 226
 227                  /*
 228                  * Adjust the mmp_check_interval depending on how much time
 229                  * it took for the MMP block to be written.
 230                  */
 231                 mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
 232                                              EXT4_MMP_MAX_CHECK_INTERVAL),
 233                                          EXT4_MMP_MIN_CHECK_INTERVAL);
 234                 mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
 235         }
 236
 237         /*
 238          * Unmount seems to be clean.
 239          */
 240         mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
 241         mmp->mmp_time = cpu_to_le64(get_seconds());
 242
 243         retval = write_mmp_block(sb, bh);
 244
 245 failed:
 246         kfree(data);
 247         brelse(bh);
 248         return retval;
 249 }
 250
 251 /*
 252  * Get a random new sequence number but make sure it is not greater than
 253  * EXT4_MMP_SEQ_MAX.
 254  */
 255 static unsigned int mmp_new_seq(void)
 256 {
 257         u32 new_seq;
 258
 259         do {
 260                 new_seq = prandom_u32();
 261         } while (new_seq > EXT4_MMP_SEQ_MAX);
 262
 263         return new_seq;
 264 }
 265
 266 /*
 267  * Protect the filesystem from being mounted more than once.
 268  */
 269 int ext4_multi_mount_protect(struct super_block *sb,
 270                                     ext4_fsblk_t mmp_block)
 271 {
 272         struct ext4_super_block *es = EXT4_SB(sb)->s_es;
 273         struct buffer_head *bh = NULL;
 274         struct mmp_struct *mmp = NULL;
 275         struct mmpd_data *mmpd_data;
 276         u32 seq;
 277         unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
 278         unsigned int wait_time = 0;
 279         int retval;
 280
 281         if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
 282             mmp_block >= ext4_blocks_count(es)) {
 283                 ext4_warning(sb, "Invalid MMP block in superblock");
 284                 goto failed;
 285         }
 286
 287         retval = read_mmp_block(sb, &bh, mmp_block);
 288         if (retval)
 289                 goto failed;
 290
 291         mmp = (struct mmp_struct *)(bh->b_data);
 292
 293         if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
 294                 mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
 295
 296         /*
 297          * If check_interval in MMP block is larger, use that instead of
 298          * update_interval from the superblock.
 299          */
 300         if (le16_to_cpu(mmp->mmp_check_interval) > mmp_check_interval)
 301                 mmp_check_interval = le16_to_cpu(mmp->mmp_check_interval);
 302
 303         seq = le32_to_cpu(mmp->mmp_seq);
 304         if (seq == EXT4_MMP_SEQ_CLEAN)
 305                 goto skip;
 306
 307         if (seq == EXT4_MMP_SEQ_FSCK) {
 308                 dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
 309                 goto failed;
 310         }
 311
 312         wait_time = min(mmp_check_interval * 2 + 1,
 313                         mmp_check_interval + 60);
 314
 315         /* Print MMP interval if more than 20 secs. */
 316         if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
 317                 ext4_warning(sb, "MMP interval %u higher than expected, please"
 318                              " wait.\n", wait_time * 2);
 319
 320         if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
 321                 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
 322                 goto failed;
 323         }
 324
 325         retval = read_mmp_block(sb, &bh, mmp_block);
 326         if (retval)
 327                 goto failed;
 328         mmp = (struct mmp_struct *)(bh->b_data);
 329         if (seq != le32_to_cpu(mmp->mmp_seq)) {
 330                 dump_mmp_msg(sb, mmp,
 331                              "Device is already active on another node.");
 332                 goto failed;
 333         }
 334
 335 skip:
 336         /*
 337          * write a new random sequence number.
 338          */
 339         seq = mmp_new_seq();
 340         mmp->mmp_seq = cpu_to_le32(seq);
 341
 342         retval = write_mmp_block(sb, bh);
 343         if (retval)
 344                 goto failed;
 345
 346         /*
 347          * wait for MMP interval and check mmp_seq.
 348          */
 349         if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
 350                 ext4_warning(sb, "MMP startup interrupted, failing mount\n");
 351                 goto failed;
 352         }
 353
 354         retval = read_mmp_block(sb, &bh, mmp_block);
 355         if (retval)
 356                 goto failed;
 357         mmp = (struct mmp_struct *)(bh->b_data);
 358         if (seq != le32_to_cpu(mmp->mmp_seq)) {
 359                 dump_mmp_msg(sb, mmp,
 360                              "Device is already active on another node.");
 361                 goto failed;
 362         }
 363
 364         mmpd_data = kmalloc(sizeof(struct mmpd_data), GFP_KERNEL);
 365         if (!mmpd_data) {
 366                 ext4_warning(sb, "not enough memory for mmpd_data");
 367                 goto failed;
 368         }
 369         mmpd_data->sb = sb;
 370         mmpd_data->bh = bh;
 371
 372         /*
 373          * Start a kernel thread to update the MMP block periodically.
 374          */
 375         EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%s",
 376                                              bdevname(bh->b_bdev,
 377                                                       mmp->mmp_bdevname));
 378         if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
 379                 EXT4_SB(sb)->s_mmp_tsk = NULL;
 380                 kfree(mmpd_data);
 381                 ext4_warning(sb, "Unable to create kmmpd thread for %s.",
 382                              sb->s_id);
 383                 goto failed;
 384         }
 385
 386         return 0;
 387
 388 failed:
 389         brelse(bh);
 390         return 1;
 391 }
 392
 393