On Fri, Feb 28, 2020 at 6:10 PM Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote:
>
> 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:
Thank you for doing that and I'm sorry that I'm replying with such a delay.
>
> (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.
Thank you for noticing.
>
> So, this function's call signature should change so that callers can
> communicate both _SHARED and _EXCL; and then you can pick the correct
Thanks for the suggestion...but that's how v5 signature looked like
before Christoph and Eric requested change...on the grounds that
there're:
* confusion over a (true, true) set of args
* confusion of what happens if we pass (false, false).
> "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)
I tried to create a table for this code as well:
readlocked y n y
writelocked *n* y y
unlocked n n n
nolockdep readlocked y y y
nolockdep writelocked y y y
nolockdep unlocked n n n
I think that when we query writelocked lock for being shared having
'no' for an answer may not be expected...or at least this is how I
read the code.
int __lock_is_held(const struct lockdep_map *lock, int read)
{
struct task_struct *curr = current;
int i;
for (i = 0; i < curr->lockdep_depth; i++) {
struct held_lock *hlock = curr->held_locks + i;
if (match_held_lock(hlock, lock)) {
if (read == -1 || hlock->read == read)
return 1;
return 0;
}
}
return 0;
}
Thanks for any comments
>
> 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
> >
>
