• Q
    btrfs: sysfs: update fs features directory asynchronously · b7625f46
    Qu Wenruo 提交于
    [BUG]
    Since the introduction of per-fs feature sysfs interface
    (/sys/fs/btrfs/<UUID>/features/), the content of that directory is never
    updated.
    
    Thus for the following case, that directory will not show the new
    features like RAID56:
    
      # mkfs.btrfs -f $dev1 $dev2 $dev3
      # mount $dev1 $mnt
      # btrfs balance start -f -mconvert=raid5 $mnt
      # ls /sys/fs/btrfs/$uuid/features/
      extended_iref  free_space_tree  no_holes  skinny_metadata
    
    While after unmount and mount, we got the correct features:
    
      # umount $mnt
      # mount $dev1 $mnt
      # ls /sys/fs/btrfs/$uuid/features/
      extended_iref  free_space_tree  no_holes  raid56 skinny_metadata
    
    [CAUSE]
    Because we never really try to update the content of per-fs features/
    directory.
    
    We had an attempt to update the features directory dynamically in commit
    14e46e04 ("btrfs: synchronize incompat feature bits with sysfs
    files"), but unfortunately it get reverted in commit e410e34f
    ("Revert "btrfs: synchronize incompat feature bits with sysfs files"").
    The problem in the original patch is, in the context of
    btrfs_create_chunk(), we can not afford to update the sysfs group.
    
    The exported but never utilized function, btrfs_sysfs_feature_update()
    is the leftover of such attempt.  As even if we go sysfs_update_group(),
    new files will need extra memory allocation, and we have no way to
    specify the sysfs update to go GFP_NOFS.
    
    [FIX]
    This patch will address the old problem by doing asynchronous sysfs
    update in the cleaner thread.
    
    This involves the following changes:
    
    - Make __btrfs_(set|clear)_fs_(incompat|compat_ro) helpers to set
      BTRFS_FS_FEATURE_CHANGED flag when needed
    
    - Update btrfs_sysfs_feature_update() to use sysfs_update_group()
      And drop unnecessary arguments.
    
    - Call btrfs_sysfs_feature_update() in cleaner_kthread
      If we have the BTRFS_FS_FEATURE_CHANGED flag set.
    
    - Wake up cleaner_kthread in btrfs_commit_transaction if we have
      BTRFS_FS_FEATURE_CHANGED flag
    
    By this, all the previously dangerous call sites like
    btrfs_create_chunk() need no new changes, as above helpers would
    have already set the BTRFS_FS_FEATURE_CHANGED flag.
    
    The real work happens at cleaner_kthread, thus we pay the cost of
    delaying the update to sysfs directory, but the delayed time should be
    small enough that end user can not distinguish though it might get
    delayed if the cleaner thread is busy with removing subvolumes or
    defrag.
    
    CC: stable@vger.kernel.org # 4.14+
    Reviewed-by: NAnand Jain <anand.jain@oracle.com>
    Signed-off-by: NQu Wenruo <wqu@suse.com>
    Reviewed-by: NDavid Sterba <dsterba@suse.com>
    Signed-off-by: NDavid Sterba <dsterba@suse.com>
    b7625f46
sysfs.c 61.9 KB