+Prevent an ext4 filesystem from being mounted multiple times.
+A sequence number is stored on disk and is periodically updated (every 5
+seconds by default) by a mounted filesystem.
+At mount time, we now wait for s_mmp_update_interval seconds to make sure
+that the MMP sequence does not change.
+In case of failure, the nodename, bdevname and the time at which the MMP
+block was last updated is displayed.
+Move all mmp code to a dedicated file (mmp.c).
+
+Signed-off-by: Andreas Dilger <adilger <at> whamcloud.com>
+Signed-off-by: Johann Lombardi <johann <at> whamcloud.com>
+---
+ fs/ext4/Makefile | 3 +-
+ fs/ext4/ext4.h | 76 ++++++++++++-
+ fs/ext4/mmp.c | 351 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ fs/ext4/super.c | 18 +++-
+ 4 files changed, 444 insertions(+), 4 deletions(-)
+ create mode 100644 fs/ext4/mmp.c
+
+Index: linux-stage/fs/ext4/Makefile
+===================================================================
+--- linux-stage.orig/fs/ext4/Makefile
++++ linux-stage/fs/ext4/Makefile
+@@ -6,7 +6,8 @@ obj-$(CONFIG_EXT4_FS) += ext4.o
+
+ ext4-y := balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o \
+ ioctl.o namei.o super.o symlink.o hash.o resize.o extents.o \
+- ext4_jbd2.o migrate.o mballoc.o block_validity.o move_extent.o
++ ext4_jbd2.o migrate.o mballoc.o block_validity.o move_extent.o \
++ mmp.o
+
+ ext4-$(CONFIG_EXT4_FS_XATTR) += xattr.o xattr_user.o xattr_trusted.o
+ ext4-$(CONFIG_EXT4_FS_POSIX_ACL) += acl.o
+Index: linux-stage/fs/ext4/ext4.h
+===================================================================
+--- linux-stage.orig/fs/ext4/ext4.h
++++ linux-stage/fs/ext4/ext4.h
+@@ -1009,7 +1009,7 @@ struct ext4_super_block {
+ __le16 s_want_extra_isize; /* New inodes should reserve # bytes */
+ __le32 s_flags; /* Miscellaneous flags */
+ __le16 s_raid_stride; /* RAID stride */
+- __le16 s_mmp_interval; /* # seconds to wait in MMP checking */
++ __le16 s_mmp_update_interval; /* # seconds to wait in MMP checking */
+ __le64 s_mmp_block; /* Block for multi-mount protection */
+ __le32 s_raid_stripe_width; /* blocks on all data disks (N*stride)*/
+ __u8 s_log_groups_per_flex; /* FLEX_BG group size */
+@@ -1177,6 +1177,9 @@ struct ext4_sb_info {
+ /* workqueue for dio unwritten */
+ struct workqueue_struct *dio_unwritten_wq;
+
++ /* Kernel thread for multiple mount protection */
++ struct task_struct *s_mmp_tsk;
++
+ /* Lazy inode table initialization info */
+ struct ext4_li_request *s_li_request;
+ /* Wait multiplier for lazy initialization thread */
+@@ -1322,7 +1325,8 @@ EXT4_INODE_BIT_FNS(state, state_flags)
+ EXT4_FEATURE_INCOMPAT_META_BG| \
+ EXT4_FEATURE_INCOMPAT_EXTENTS| \
+ EXT4_FEATURE_INCOMPAT_64BIT| \
+- EXT4_FEATURE_INCOMPAT_FLEX_BG)
++ EXT4_FEATURE_INCOMPAT_FLEX_BG| \
++ EXT4_FEATURE_INCOMPAT_MMP)
+ #define EXT4_FEATURE_RO_COMPAT_SUPP (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
+ EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
+ EXT4_FEATURE_RO_COMPAT_GDT_CSUM| \
+@@ -1576,6 +1580,67 @@ struct ext4_features {
+ };
+
+ /*
++ * This structure will be used for multiple mount protection. It will be
++ * written into the block number saved in the s_mmp_block field in the
++ * superblock. Programs that check MMP should assume that if
++ * SEQ_FSCK (or any unknown code above SEQ_MAX) is present then it is NOT safe
++ * to use the filesystem, regardless of how old the timestamp is.
++ */
++#define EXT4_MMP_MAGIC 0x004D4D50U /* ASCII for MMP */
++#define EXT4_MMP_SEQ_CLEAN 0xFF4D4D50U /* mmp_seq value for clean unmount */
++#define EXT4_MMP_SEQ_FSCK 0xE24D4D50U /* mmp_seq value when being fscked */
++#define EXT4_MMP_SEQ_MAX 0xE24D4D4FU /* maximum valid mmp_seq value */
++
++struct mmp_struct {
++ __le32 mmp_magic; /* Magic number for MMP */
++ __le32 mmp_seq; /* Sequence no. updated periodically */
++
++ /*
++ * mmp_time, mmp_nodename & mmp_bdevname are only used for information
++ * purposes and do not affect the correctness of the algorithm
++ */
++ __le64 mmp_time; /* Time last updated */
++ char mmp_nodename[64]; /* Node which last updated MMP block */
++ char mmp_bdevname[32]; /* Bdev which last updated MMP block */
++
++ /*
++ * mmp_check_interval is used to verify if the MMP block has been
++ * updated on the block device. The value is updated based on the
++ * maximum time to write the MMP block during an update cycle.
++ */
++ __le16 mmp_check_interval;
++
++ __le16 mmp_pad1;
++ __le32 mmp_pad2[227];
++};
++
++/* arguments passed to the mmp thread */
++struct mmpd_data {
++ struct buffer_head *bh; /* bh from initial read_mmp_block() */
++ struct super_block *sb; /* super block of the fs */
++};
++
++/*
++ * Check interval multiplier
++ * The MMP block is written every update interval and initially checked every
++ * update interval x the multiplier (the value is then adapted based on the
++ * write latency). The reason is that writes can be delayed under load and we
++ * don't want readers to incorrectly assume that the filesystem is no longer
++ * in use.
++ */
++#define EXT4_MMP_CHECK_MULT 2UL
++
++/*
++ * Minimum interval for MMP checking in seconds.
++ */
++#define EXT4_MMP_MIN_CHECK_INTERVAL 5UL
++
++/*
++ * Maximum interval for MMP checking in seconds.
++ */
++#define EXT4_MMP_MAX_CHECK_INTERVAL 300UL
++
++/*
+ * Function prototypes
+ */
+
+@@ -1757,6 +1822,10 @@ extern void __ext4_warning(struct super_
+ #define ext4_warning(sb, message...) __ext4_warning(sb, __func__, ## message)
+ extern void ext4_msg(struct super_block *, const char *, const char *, ...)
+ __attribute__ ((format (printf, 3, 4)));
++extern void __dump_mmp_msg(struct super_block *, struct mmp_struct *mmp,
++ const char *, const char *);
++#define dump_mmp_msg(sb, mmp, msg) __dump_mmp_msg(sb, mmp, __func__, \
++ msg)
+ extern void ext4_grp_locked_error(struct super_block *, ext4_group_t,
+ const char *, const char *, ...)
+ __attribute__ ((format (printf, 4, 5)));
+@@ -2050,6 +2119,8 @@ extern int ext4_move_extents(struct file
+ __u64 start_orig, __u64 start_donor,
+ __u64 len, __u64 *moved_len);
+
++/* mmp.c */
++extern int ext4_multi_mount_protect(struct super_block *, ext4_fsblk_t);
+
+ /*
+ * Add new method to test wether block and inode bitmaps are properly
+Index: linux-stage/fs/ext4/mmp.c
+===================================================================
+--- /dev/null
++++ linux-stage/fs/ext4/mmp.c
+@@ -0,0 +1,351 @@
++#include <linux/fs.h>
++#include <linux/random.h>
++#include <linux/buffer_head.h>
++#include <linux/utsname.h>
++#include <linux/kthread.h>
++
++#include "ext4.h"
++
++/*
++ * Write the MMP block using WRITE_SYNC to try to get the block on-disk
++ * faster.
++ */
++static int write_mmp_block(struct buffer_head *bh)
++{
++ mark_buffer_dirty(bh);
++ lock_buffer(bh);
++ bh->b_end_io = end_buffer_write_sync;
++ get_bh(bh);
++ submit_bh(WRITE_SYNC, bh);
++ wait_on_buffer(bh);
++ if (unlikely(!buffer_uptodate(bh)))
++ return 1;
++
++ return 0;
++}
++
++/*
++ * Read the MMP block. It _must_ be read from disk and hence we clear the
++ * uptodate flag on the buffer.
++ */
++static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
++ ext4_fsblk_t mmp_block)
++{
++ struct mmp_struct *mmp;
++
++ if (*bh)
++ clear_buffer_uptodate(*bh);
++
++ /* This would be sb_bread(sb, mmp_block), except we need to be sure
++ * that the MD RAID device cache has been bypassed, and that the read
++ * is not blocked in the elevator. */
++ if (!*bh)
++ *bh = sb_getblk(sb, mmp_block);
++ if (*bh) {
++ get_bh(*bh);
++ lock_buffer(*bh);
++ (*bh)->b_end_io = end_buffer_read_sync;
++ submit_bh(READ_SYNC, *bh);
++ wait_on_buffer(*bh);
++ if (!buffer_uptodate(*bh)) {
++ brelse(*bh);
++ *bh = NULL;
++ }
++ }
++ if (!*bh) {
++ ext4_warning(sb, "Error while reading MMP block %llu",
++ mmp_block);
++ return -EIO;
++ }
++
++ mmp = (struct mmp_struct *)((*bh)->b_data);
++ if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC)
++ return -EINVAL;
++
++ return 0;
++}
++
++/*
++ * Dump as much information as possible to help the admin.
++ */
++void __dump_mmp_msg(struct super_block *sb, struct mmp_struct *mmp,
++ const char *function, const char *msg)
++{
++ __ext4_warning(sb, function, msg);
++ __ext4_warning(sb, function,
++ "MMP failure info: last update time: %llu, last update "
++ "node: %s, last update device: %s\n",
++ (long long unsigned int) le64_to_cpu(mmp->mmp_time),
++ mmp->mmp_nodename, mmp->mmp_bdevname);
++}
++
++/*
++ * kmmpd will update the MMP sequence every s_mmp_update_interval seconds
++ */
++static int kmmpd(void *data)
++{
++ struct super_block *sb = ((struct mmpd_data *) data)->sb;
++ struct buffer_head *bh = ((struct mmpd_data *) data)->bh;
++ struct ext4_super_block *es = EXT4_SB(sb)->s_es;
++ struct mmp_struct *mmp;
++ ext4_fsblk_t mmp_block;
++ u32 seq = 0;
++ unsigned long failed_writes = 0;
++ int mmp_update_interval = le16_to_cpu(es->s_mmp_update_interval);
++ unsigned mmp_check_interval;
++ unsigned long last_update_time;
++ unsigned long diff;
++ int retval;
++
++ mmp_block = le64_to_cpu(es->s_mmp_block);
++ mmp = (struct mmp_struct *)(bh->b_data);
++ mmp->mmp_time = cpu_to_le64(get_seconds());
++ /*
++ * Start with the higher mmp_check_interval and reduce it if
++ * the MMP block is being updated on time.
++ */
++ mmp_check_interval = max(EXT4_MMP_CHECK_MULT * mmp_update_interval,
++ EXT4_MMP_MIN_CHECK_INTERVAL);
++ mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
++ bdevname(bh->b_bdev, mmp->mmp_bdevname);
++
++ memcpy(mmp->mmp_nodename, init_utsname()->nodename,
++ sizeof(mmp->mmp_nodename));
++
++ while (!kthread_should_stop()) {
++ if (++seq > EXT4_MMP_SEQ_MAX)
++ seq = 1;
++
++ mmp->mmp_seq = cpu_to_le32(seq);
++ mmp->mmp_time = cpu_to_le64(get_seconds());
++ last_update_time = jiffies;
++
++ retval = write_mmp_block(bh);
++ /*
++ * Don't spew too many error messages. Print one every
++ * (s_mmp_update_interval * 60) seconds.
++ */
++ if (retval) {
++ if ((failed_writes % 60) == 0)
++ ext4_error(sb, "Error writing to MMP block");
++ failed_writes++;
++ }
++
++ if (!(le32_to_cpu(es->s_feature_incompat) &
++ EXT4_FEATURE_INCOMPAT_MMP)) {
++ ext4_warning(sb, "kmmpd being stopped since MMP feature"
++ " has been disabled.");
++ EXT4_SB(sb)->s_mmp_tsk = NULL;
++ goto failed;
++ }
++
++ if (sb->s_flags & MS_RDONLY) {
++ ext4_warning(sb, "kmmpd being stopped since filesystem "
++ "has been remounted as readonly.");
++ EXT4_SB(sb)->s_mmp_tsk = NULL;
++ goto failed;
++ }
++
++ diff = jiffies - last_update_time;
++ if (diff < mmp_update_interval * HZ)
++ schedule_timeout_interruptible(mmp_update_interval *
++ HZ - diff);
++
++ /*
++ * We need to make sure that more than mmp_check_interval
++ * seconds have not passed since writing. If that has happened
++ * we need to check if the MMP block is as we left it.
++ */
++ diff = jiffies - last_update_time;
++ if (diff > mmp_check_interval * HZ) {
++ struct buffer_head *bh_check = NULL;
++ struct mmp_struct *mmp_check;
++
++ retval = read_mmp_block(sb, &bh_check, mmp_block);
++ if (retval) {
++ ext4_error(sb, "error reading MMP data: %d",
++ retval);
++
++ EXT4_SB(sb)->s_mmp_tsk = NULL;
++ goto failed;
++ }
++
++ mmp_check = (struct mmp_struct *)(bh_check->b_data);
++ if (mmp->mmp_seq != mmp_check->mmp_seq ||
++ memcmp(mmp->mmp_nodename, mmp_check->mmp_nodename,
++ sizeof(mmp->mmp_nodename))) {
++ dump_mmp_msg(sb, mmp_check,
++ "Error while updating MMP info. "
++ "The filesystem seems to have been"
++ " multiply mounted.");
++ ext4_error(sb, "abort");
++ goto failed;
++ }
++ put_bh(bh_check);
++ }
++
++ /*
++ * Adjust the mmp_check_interval depending on how much time
++ * it took for the MMP block to be written.
++ */
++ mmp_check_interval = max(min(EXT4_MMP_CHECK_MULT * diff / HZ,
++ EXT4_MMP_MAX_CHECK_INTERVAL),
++ EXT4_MMP_MIN_CHECK_INTERVAL);
++ mmp->mmp_check_interval = cpu_to_le16(mmp_check_interval);
++ }
++
++ /*
++ * Unmount seems to be clean.
++ */
++ mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
++ mmp->mmp_time = cpu_to_le64(get_seconds());
++
++ retval = write_mmp_block(bh);
++
++failed:
++ kfree(data);
++ brelse(bh);
++ return retval;
++}
++
++/*
++ * Get a random new sequence number but make sure it is not greater than
++ * EXT4_MMP_SEQ_MAX.
++ */
++static unsigned int mmp_new_seq(void)
++{
++ u32 new_seq;
++
++ do {
++ get_random_bytes(&new_seq, sizeof(u32));
++ } while (new_seq > EXT4_MMP_SEQ_MAX);
++
++ return new_seq;
++}
++
++/*
++ * Protect the filesystem from being mounted more than once.
++ */
++int ext4_multi_mount_protect(struct super_block *sb,
++ ext4_fsblk_t mmp_block)
++{
++ struct ext4_super_block *es = EXT4_SB(sb)->s_es;
++ struct buffer_head *bh = NULL;
++ struct mmp_struct *mmp = NULL;
++ struct mmpd_data *mmpd_data;
++ u32 seq;
++ unsigned int mmp_check_interval = le16_to_cpu(es->s_mmp_update_interval);
++ unsigned int wait_time = 0;
++ int retval;
++
++ if (mmp_block < le32_to_cpu(es->s_first_data_block) ||
++ mmp_block >= ext4_blocks_count(es)) {
++ ext4_warning(sb, "Invalid MMP block in superblock");
++ goto failed;
++ }
++
++ retval = read_mmp_block(sb, &bh, mmp_block);
++ if (retval)
++ goto failed;
++
++ mmp = (struct mmp_struct *)(bh->b_data);
++
++ if (mmp_check_interval < EXT4_MMP_MIN_CHECK_INTERVAL)
++ mmp_check_interval = EXT4_MMP_MIN_CHECK_INTERVAL;
++
++ /*
++ * If check_interval in MMP block is larger, use that instead of
++ * update_interval from the superblock.
++ */
++ if (mmp->mmp_check_interval > mmp_check_interval)
++ mmp_check_interval = mmp->mmp_check_interval;
++
++ seq = le32_to_cpu(mmp->mmp_seq);
++ if (seq == EXT4_MMP_SEQ_CLEAN)
++ goto skip;
++
++ if (seq == EXT4_MMP_SEQ_FSCK) {
++ dump_mmp_msg(sb, mmp, "fsck is running on the filesystem");
++ goto failed;
++ }
++
++ wait_time = min(mmp_check_interval * 2 + 1,
++ mmp_check_interval + 60);
++
++ /* Print MMP interval if more than 20 secs. */
++ if (wait_time > EXT4_MMP_MIN_CHECK_INTERVAL * 4)
++ ext4_warning(sb, "MMP interval %u higher than expected, please"
++ " wait.\n", wait_time * 2);
++
++ if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
++ ext4_warning(sb, "MMP startup interrupted, failing mount\n");
++ goto failed;
++ }
++
++ retval = read_mmp_block(sb, &bh, mmp_block);
++ if (retval)
++ goto failed;
++ mmp = (struct mmp_struct *)(bh->b_data);
++ if (seq != le32_to_cpu(mmp->mmp_seq)) {
++ dump_mmp_msg(sb, mmp,
++ "Device is already active on another node.");
++ goto failed;
++ }
++
++skip:
++ /*
++ * write a new random sequence number.
++ */
++ mmp->mmp_seq = seq = cpu_to_le32(mmp_new_seq());
++
++ retval = write_mmp_block(bh);
++ if (retval)
++ goto failed;
++
++ /*
++ * wait for MMP interval and check mmp_seq.
++ */
++ if (schedule_timeout_interruptible(HZ * wait_time) != 0) {
++ ext4_warning(sb, "MMP startup interrupted, failing mount\n");
++ goto failed;
++ }
++
++ retval = read_mmp_block(sb, &bh, mmp_block);
++ if (retval)
++ goto failed;
++ mmp = (struct mmp_struct *)(bh->b_data);
++ if (seq != le32_to_cpu(mmp->mmp_seq)) {
++ dump_mmp_msg(sb, mmp,
++ "Device is already active on another node.");
++ goto failed;
++ }
++
++ mmpd_data = kmalloc(sizeof(struct mmpd_data), GFP_KERNEL);
++ if (!mmpd_data) {
++ ext4_warning(sb, "not enough memory for mmpd_data");
++ goto failed;
++ }
++ mmpd_data->sb = sb;
++ mmpd_data->bh = bh;
++
++ /*
++ * Start a kernel thread to update the MMP block periodically.
++ */
++ EXT4_SB(sb)->s_mmp_tsk = kthread_run(kmmpd, mmpd_data, "kmmpd-%s",
++ bdevname(bh->b_bdev,
++ mmp->mmp_bdevname));
++ if (IS_ERR(EXT4_SB(sb)->s_mmp_tsk)) {
++ EXT4_SB(sb)->s_mmp_tsk = NULL;
++ kfree(mmpd_data);
++ ext4_warning(sb, "Unable to create kmmpd thread for %s.",
++ sb->s_id);
++ goto failed;
++ }
++
++ return 0;
++
++failed:
++ brelse(bh);
++ return 1;
++}
++
+Index: linux-stage/fs/ext4/super.c
+===================================================================
+--- linux-stage.orig/fs/ext4/super.c
++++ linux-stage/fs/ext4/super.c
+@@ -40,6 +40,8 @@
+ #include <linux/log2.h>
+ #include <linux/crc16.h>
+ #include <asm/uaccess.h>
++#include <linux/kthread.h>
++#include <linux/utsname.h>
+
+ #include <linux/kthread.h>
+ #include <linux/freezer.h>
+@@ -716,6 +718,8 @@ static void ext4_put_super(struct super_
+ invalidate_bdev(sbi->journal_bdev);
+ ext4_blkdev_remove(sbi);
+ }
++ if (sbi->s_mmp_tsk)
++ kthread_stop(sbi->s_mmp_tsk);
+ sb->s_fs_info = NULL;
+ /*
+ * Now that we are completely done shutting down the
+@@ -3241,6 +3245,10 @@ static int ext4_fill_super(struct super_
+ needs_recovery = (es->s_last_orphan != 0 ||
+ EXT4_HAS_INCOMPAT_FEATURE(sb,
+ EXT4_FEATURE_INCOMPAT_RECOVER));
++ if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_MMP) &&
++ !(sb->s_flags & MS_RDONLY))
++ if (ext4_multi_mount_protect(sb, le64_to_cpu(es->s_mmp_block)))
++ goto failed_mount3;
+
+ /*
+ * The first inode we look at is the journal inode. Don't try
+@@ -3491,6 +3499,8 @@ failed_mount3:
+ percpu_counter_destroy(&sbi->s_freeinodes_counter);
+ percpu_counter_destroy(&sbi->s_dirs_counter);
+ percpu_counter_destroy(&sbi->s_dirtyblocks_counter);
++ if (sbi->s_mmp_tsk)
++ kthread_stop(sbi->s_mmp_tsk);
+ failed_mount2:
+ for (i = 0; i < db_count; i++)
+ brelse(sbi->s_group_desc[i]);
+@@ -4001,7 +4011,7 @@ static int ext4_remount(struct super_blo
+ int enable_quota = 0;
+ ext4_group_t g;
+ unsigned int journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
+- int err;
++ int err = 0;
+ #ifdef CONFIG_QUOTA
+ int i;
+ #endif
+@@ -4129,6 +4139,13 @@ static int ext4_remount(struct super_blo
+ goto restore_opts;
+ if (!ext4_setup_super(sb, es, 0))
+ sb->s_flags &= ~MS_RDONLY;
++ if (EXT4_HAS_INCOMPAT_FEATURE(sb,
++ EXT4_FEATURE_INCOMPAT_MMP))
++ if (ext4_multi_mount_protect(sb,
++ le64_to_cpu(es->s_mmp_block))) {
++ err = -EROFS;
++ goto restore_opts;
++ }
+ enable_quota = 1;
+ }
+ }
git://git.whamcloud.com / fs / lustre-release.git / commitdiff