On Thu, Feb 27, 2020 at 09:36:33PM +0100, Pavel Reichl wrote:
> Refactor xfs_isilocked() to use newly introduced __xfs_rwsem_islocked().
> __xfs_rwsem_islocked() is a helper function which encapsulates checking
> state of rw_semaphores hold by inode.
>
> Signed-off-by: Pavel Reichl <preichl@xxxxxxxxxx>
> Suggested-by: Dave Chinner <dchinner@xxxxxxxxxx>
> Suggested-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
> Changes from V5:
> Drop shared flag from __xfs_rwsem_islocked()
>
>
> fs/xfs/xfs_inode.c | 42 ++++++++++++++++++++++++++----------------
> fs/xfs/xfs_inode.h | 2 +-
> 2 files changed, 27 insertions(+), 17 deletions(-)
>
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index c5077e6326c7..4faf7827717b 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -345,32 +345,42 @@ xfs_ilock_demote(
> }
>
> #if defined(DEBUG) || defined(XFS_WARN)
> -int
> +static inline bool
> +__xfs_rwsem_islocked(
> + struct rw_semaphore *rwsem,
> + bool excl)
> +{
> + if (!rwsem_is_locked(rwsem))
> + return false;
So, uh, I finally made the time to dig through what exactly lockdep
provides as far as testing functions, and came up with the following
truth table for the old xfs_isilocked behavior w.r.t. IOLOCK:
(nolockdep corresponds to debug_locks == 0)
RWSEM STATE PARAMETERS TO XFS_ISILOCKED:
SHARED EXCL SHARED | EXCL
readlocked y n y
writelocked y y y
unlocked n n n
nolockdep readlocked y y y
nolockdep writelocked y y y
nolockdep unlocked n y n
Note that EXCL × nolockdep_unlocked returns an incorrect result, but
because we only use it with ASSERTs there haven't been any failures
reported.
And here's your new version:
readlocked y y y
writelocked y n n
unlocked n n n
nolockdep readlocked y y y
nolockdep writelocked y y y
nolockdep unlocked n n n
Thanks for fixing the false positive that I mentioned above.
> +
> + if (debug_locks && excl)
> + return lockdep_is_held_type(rwsem, 1);
This is wrong, the second parameter of lockdep_is_held_type is 0 to test
if the rwsem is write-locked; 1 to test if it is read-locked; or -1 to
test if the rwsem is read or write-locked.
So, this function's call signature should change so that callers can
communicate both _SHARED and _EXCL; and then you can pick the correct
"r" parameter value for the lockdep_is_held_type() call. Then all of
this becomes:
if !debug_locks:
return rwsem_is_locked(rwsem)
if shared and excl:
r = -1
elif shared:
r = 1
else:
r = 0
return lockdep_is_held_type(rwsem, r)
Note also that you don't necessarily need to pass shared and excl as
separate parameters (as you did in v3); the XFS_*LOCK_{EXCL,SHARED}
definitions enable you to take care of all that with some clever bit
shifting and masking.
--D
> +
> + return true;
> +}
> +
> +bool
> xfs_isilocked(
> - xfs_inode_t *ip,
> + struct xfs_inode *ip,
> uint lock_flags)
> {
> - if (lock_flags & (XFS_ILOCK_EXCL|XFS_ILOCK_SHARED)) {
> - if (!(lock_flags & XFS_ILOCK_SHARED))
> - return !!ip->i_lock.mr_writer;
> - return rwsem_is_locked(&ip->i_lock.mr_lock);
> + if (lock_flags & (XFS_ILOCK_EXCL | XFS_ILOCK_SHARED)) {
> + return __xfs_rwsem_islocked(&ip->i_lock.mr_lock,
> + (lock_flags & XFS_ILOCK_EXCL));
> }
>
> - if (lock_flags & (XFS_MMAPLOCK_EXCL|XFS_MMAPLOCK_SHARED)) {
> - if (!(lock_flags & XFS_MMAPLOCK_SHARED))
> - return !!ip->i_mmaplock.mr_writer;
> - return rwsem_is_locked(&ip->i_mmaplock.mr_lock);
> + if (lock_flags & (XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)) {
> + return __xfs_rwsem_islocked(&ip->i_mmaplock.mr_lock,
> + (lock_flags & XFS_MMAPLOCK_EXCL));
> }
>
> - if (lock_flags & (XFS_IOLOCK_EXCL|XFS_IOLOCK_SHARED)) {
> - if (!(lock_flags & XFS_IOLOCK_SHARED))
> - return !debug_locks ||
> - lockdep_is_held_type(&VFS_I(ip)->i_rwsem, 0);
> - return rwsem_is_locked(&VFS_I(ip)->i_rwsem);
> + if (lock_flags & (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED)) {
> + return __xfs_rwsem_islocked(&VFS_I(ip)->i_rwsem,
> + (lock_flags & XFS_IOLOCK_EXCL));
> }
>
> ASSERT(0);
> - return 0;
> + return false;
> }
> #endif
>
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index 492e53992fa9..3d7ce355407d 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -416,7 +416,7 @@ void xfs_ilock(xfs_inode_t *, uint);
> int xfs_ilock_nowait(xfs_inode_t *, uint);
> void xfs_iunlock(xfs_inode_t *, uint);
> void xfs_ilock_demote(xfs_inode_t *, uint);
> -int xfs_isilocked(xfs_inode_t *, uint);
> +bool xfs_isilocked(xfs_inode_t *, uint);
> uint xfs_ilock_data_map_shared(struct xfs_inode *);
> uint xfs_ilock_attr_map_shared(struct xfs_inode *);
>
> --
> 2.24.1
>
