• Filipe Manana's avatar
    Btrfs: fix race deleting block group from space_info->ro_bgs list · 75c68e9f
    Filipe Manana authored
    When removing a block group we were deleting it from its space_info's
    ro_bgs list without the correct protection - the space info's spinlock.
    Fix this by doing the list delete while holding the spinlock of the
    corresponding space info, which is the correct lock for any operation
    on that list.
    
    This issue was introduced in the 3.19 kernel by the following change:
    
        Btrfs: move read only block groups onto their own list V2
        commit 633c0aad
    
    I ran into a kernel crash while a task was running statfs, which iterates
    the space_info->ro_bgs list while holding the space info's spinlock,
    and another task was deleting it from the same list, without holding that
    spinlock, as part of the block group remove operation (while running the
    function btrfs_remove_block_group). This happened often when running the
    stress test xfstests/generic/038 I recently made.
    Signed-off-by: default avatarFilipe Manana <fdmanana@suse.com>
    Signed-off-by: default avatarChris Mason <clm@fb.com>
    75c68e9f
extent-tree.c 261 KB