On Fri, Feb 21, 2020 at 12:34:51PM +1100, Dave Chinner wrote:
> On Thu, Feb 20, 2020 at 04:41:23PM -0800, ira.weiny@xxxxxxxxx wrote:
> > From: Ira Weiny <ira.weiny@xxxxxxxxx>
> >
> > xfs_isilocked() can't work fully without CONFIG_LOCKDEP. However,
> > making xfs_isilocked() dependant on CONFIG_LOCKDEP is not feasible
> > because it is used for more than the i_rwsem. Therefore a short-circuit
> > was provided via debug_locks. However, this caused confusion while
> > working through the xfs locking.
> >
> > Rather than use debug_locks as a flag specify this clearly using
> > IS_ENABLED(CONFIG_LOCKDEP).
> >
> > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> >
> > ---
> > Changes from V3:
> > Reordered to be a "pre-cleanup" patch
> >
> > Changes from V2:
> > This patch is new for V3
> > ---
> > fs/xfs/xfs_inode.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > index c5077e6326c7..35df324875db 100644
> > --- a/fs/xfs/xfs_inode.c
> > +++ b/fs/xfs/xfs_inode.c
> > @@ -364,7 +364,7 @@ xfs_isilocked(
> >
> > if (lock_flags & (XFS_IOLOCK_EXCL|XFS_IOLOCK_SHARED)) {
> > if (!(lock_flags & XFS_IOLOCK_SHARED))
> > - return !debug_locks ||
> > + return !IS_ENABLED(CONFIG_LOCKDEP) ||
> > lockdep_is_held_type(&VFS_I(ip)->i_rwsem, 0);
>
> This breaks expected lockdep behaviour.
>
> We need to use debug_locks here because lockdep turns off lock
> checking via debug_locks when lockdep encounters a locking
> inconsistency. We only want to know about the first locking
> problem, not spew cascading lock problems over and over once we
> already know there is a locking problem.
Ah... ok... Seems like that should be part of the lockdep interface...
I'll drop the patch for now,
Ira
>
> IOWs, checking debug_locks is required here for the same reason it
> is used in lockdep_assert_held_{read/write}(). essentially we are
> open coding lockdep_assert_held_write() here because this function
> is only called from within ASSERT() statements and we don't want
> multiple WARN/BUGs being issued when this triggers....
>
> Cheers,
>
> Dave.
> --
> Dave Chinner
> david@xxxxxxxxxxxxx
