[PATCH v3 0/1] btrfs: Use exclusive lock for file_remove_privs

[Bernd Schubert <bschubert@ddn.com>]

While adding shared direct IO write locks to fuse Miklos noticed
that file_remove_privs() needs an exclusive lock. I then
noticed that btrfs actually has the same issue as I had in my patch,
it was calling into that function with a shared lock.
This series adds a new exported function file_needs_remove_privs(),
which used by the follow up btrfs patch and will be used by the
DIO code path in fuse as well. If that function returns any mask
the shared lock needs to be dropped and replaced by the exclusive
variant.

Note: Compilation tested only.

v3: Removed file_needs_remove_privs, btrfs can check for S_NOSEC.
Christoph had suggested to benchmark if using file_remove_privs
has any performance improvement before using it, but I'm not sure
what exactly to run and actually I think IS_NOSEC should be fine
for local block device file systems. The actual patch got also
easier to read with that.

v2:
Already check for IS_NOSEC in btrfs_direct_write before the first
lock is taken.
Slight modification to make the code easier to read (boolean pointer
is passed to btrfs_write_check, instead of flags).

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Dharmendra Singh <dsingh@ddn.com>
Cc: David Sterba <dsterba@suse.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-btrfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org


Bernd Schubert (1):
  btrfs: file_remove_privs needs an exclusive lock

 fs/btrfs/file.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

-- 
2.39.2