• Filipe Manana's avatar
    Btrfs: fix file/data loss caused by fsync after rename and new inode · 56f23fdb
    Filipe Manana authored
    If we rename an inode A (be it a file or a directory), create a new
    inode B with the old name of inode A and under the same parent directory,
    fsync inode B and then power fail, at log tree replay time we end up
    removing inode A completely. If inode A is a directory then all its files
    are gone too.
    
    Example scenarios where this happens:
    This is reproducible with the following steps, taken from a couple of
    test cases written for fstests which are going to be submitted upstream
    soon:
    
       # Scenario 1
    
       mkfs.btrfs -f /dev/sdc
       mount /dev/sdc /mnt
       mkdir -p /mnt/a/x
       echo "hello" > /mnt/a/x/foo
       echo "world" > /mnt/a/x/bar
       sync
       mv /mnt/a/x /mnt/a/y
       mkdir /mnt/a/x
       xfs_io -c fsync /mnt/a/x
       <power failure happens>
    
       The next time the fs is mounted, log tree replay happens and
       the directory "y" does not exist nor do the files "foo" and
       "bar" exist anywhere (neither in "y" nor in "x", nor the root
       nor anywhere).
    
       # Scenario 2
    
       mkfs.btrfs -f /dev/sdc
       mount /dev/sdc /mnt
       mkdir /mnt/a
       echo "hello" > /mnt/a/foo
       sync
       mv /mnt/a/foo /mnt/a/bar
       echo "world" > /mnt/a/foo
       xfs_io -c fsync /mnt/a/foo
       <power failure happens>
    
       The next time the fs is mounted, log tree replay happens and the
       file "bar" does not exists anymore. A file with the name "foo"
       exists and it matches the second file we created.
    
    Another related problem that does not involve file/data loss is when a
    new inode is created with the name of a deleted snapshot and we fsync it:
    
       mkfs.btrfs -f /dev/sdc
       mount /dev/sdc /mnt
       mkdir /mnt/testdir
       btrfs subvolume snapshot /mnt /mnt/testdir/snap
       btrfs subvolume delete /mnt/testdir/snap
       rmdir /mnt/testdir
       mkdir /mnt/testdir
       xfs_io -c fsync /mnt/testdir # or fsync some file inside /mnt/testdir
       <power failure>
    
       The next time the fs is mounted the log replay procedure fails because
       it attempts to delete the snapshot entry (which has dir item key type
       of BTRFS_ROOT_ITEM_KEY) as if it were a regular (non-root) entry,
       resulting in the following error that causes mount to fail:
    
       [52174.510532] BTRFS info (device dm-0): failed to delete reference to snap, inode 257 parent 257
       [52174.512570] ------------[ cut here ]------------
       [52174.513278] WARNING: CPU: 12 PID: 28024 at fs/btrfs/inode.c:3986 __btrfs_unlink_inode+0x178/0x351 [btrfs]()
       [52174.514681] BTRFS: Transaction aborted (error -2)
       [52174.515630] Modules linked in: btrfs dm_flakey dm_mod overlay crc32c_generic ppdev xor raid6_pq acpi_cpufreq parport_pc tpm_tis sg parport tpm evdev i2c_piix4 proc
       [52174.521568] CPU: 12 PID: 28024 Comm: mount Tainted: G        W       4.5.0-rc6-btrfs-next-27+ #1
       [52174.522805] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS by qemu-project.org 04/01/2014
       [52174.524053]  0000000000000000 ffff8801df2a7710 ffffffff81264e93 ffff8801df2a7758
       [52174.524053]  0000000000000009 ffff8801df2a7748 ffffffff81051618 ffffffffa03591cd
       [52174.524053]  00000000fffffffe ffff88015e6e5000 ffff88016dbc3c88 ffff88016dbc3c88
       [52174.524053] Call Trace:
       [52174.524053]  [<ffffffff81264e93>] dump_stack+0x67/0x90
       [52174.524053]  [<ffffffff81051618>] warn_slowpath_common+0x99/0xb2
       [52174.524053]  [<ffffffffa03591cd>] ? __btrfs_unlink_inode+0x178/0x351 [btrfs]
       [52174.524053]  [<ffffffff81051679>] warn_slowpath_fmt+0x48/0x50
       [52174.524053]  [<ffffffffa03591cd>] __btrfs_unlink_inode+0x178/0x351 [btrfs]
       [52174.524053]  [<ffffffff8118f5e9>] ? iput+0xb0/0x284
       [52174.524053]  [<ffffffffa0359fe8>] btrfs_unlink_inode+0x1c/0x3d [btrfs]
       [52174.524053]  [<ffffffffa038631e>] check_item_in_log+0x1fe/0x29b [btrfs]
       [52174.524053]  [<ffffffffa0386522>] replay_dir_deletes+0x167/0x1cf [btrfs]
       [52174.524053]  [<ffffffffa038739e>] fixup_inode_link_count+0x289/0x2aa [btrfs]
       [52174.524053]  [<ffffffffa038748a>] fixup_inode_link_counts+0xcb/0x105 [btrfs]
       [52174.524053]  [<ffffffffa038a5ec>] btrfs_recover_log_trees+0x258/0x32c [btrfs]
       [52174.524053]  [<ffffffffa03885b2>] ? replay_one_extent+0x511/0x511 [btrfs]
       [52174.524053]  [<ffffffffa034f288>] open_ctree+0x1dd4/0x21b9 [btrfs]
       [52174.524053]  [<ffffffffa032b753>] btrfs_mount+0x97e/0xaed [btrfs]
       [52174.524053]  [<ffffffff8108e1b7>] ? trace_hardirqs_on+0xd/0xf
       [52174.524053]  [<ffffffff8117bafa>] mount_fs+0x67/0x131
       [52174.524053]  [<ffffffff81193003>] vfs_kern_mount+0x6c/0xde
       [52174.524053]  [<ffffffffa032af81>] btrfs_mount+0x1ac/0xaed [btrfs]
       [52174.524053]  [<ffffffff8108e1b7>] ? trace_hardirqs_on+0xd/0xf
       [52174.524053]  [<ffffffff8108c262>] ? lockdep_init_map+0xb9/0x1b3
       [52174.524053]  [<ffffffff8117bafa>] mount_fs+0x67/0x131
       [52174.524053]  [<ffffffff81193003>] vfs_kern_mount+0x6c/0xde
       [52174.524053]  [<ffffffff8119590f>] do_mount+0x8a6/0x9e8
       [52174.524053]  [<ffffffff811358dd>] ? strndup_user+0x3f/0x59
       [52174.524053]  [<ffffffff81195c65>] SyS_mount+0x77/0x9f
       [52174.524053]  [<ffffffff814935d7>] entry_SYSCALL_64_fastpath+0x12/0x6b
       [52174.561288] ---[ end trace 6b53049efb1a3ea6 ]---
    
    Fix this by forcing a transaction commit when such cases happen.
    This means we check in the commit root of the subvolume tree if there
    was any other inode with the same reference when the inode we are
    fsync'ing is a new inode (created in the current transaction).
    
    Test cases for fstests, covering all the scenarios given above, were
    submitted upstream for fstests:
    
      * fstests: generic test for fsync after renaming directory
        https://patchwork.kernel.org/patch/8694281/
    
      * fstests: generic test for fsync after renaming file
        https://patchwork.kernel.org/patch/8694301/
    
      * fstests: add btrfs test for fsync after snapshot deletion
        https://patchwork.kernel.org/patch/8670671/
    
    
    
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
    Signed-off-by: default avatarChris Mason <clm@fb.com>
    56f23fdb
tree-log.c 153 KB