On Mon, Oct 12, 2020 at 11:02:51PM +0200, Pavel Reichl wrote:
>
> > ...
> >> @@ -384,16 +385,17 @@ xfs_isilocked(
> >> 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)) {
> >> + ASSERT(!(lock_flags & ~(XFS_ILOCK_EXCL | XFS_ILOCK_SHARED)));
> >> + return __xfs_rwsem_islocked(&ip->i_lock,
> >> + (lock_flags >> XFS_ILOCK_FLAG_SHIFT));
> >> }
> >>
> >> - 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)) {
> >> + ASSERT(!(lock_flags &
> >> + ~(XFS_MMAPLOCK_EXCL | XFS_MMAPLOCK_SHARED)));
> >> + return __xfs_rwsem_islocked(&ip->i_mmaplock,
> >> + (lock_flags >> XFS_MMAPLOCK_FLAG_SHIFT));
> >> }
> >>
> >> if (lock_flags & (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED)) {
> >
> > Can we add a similar assert for this case as we have for the others?
> > Otherwise the rest looks fairly straightforward to me.
> >
>
> Sure we can! But do we want to?
>
> I think that these asserts are supposed to make sure that only flags for one of the inode's locks are used eg. ILOCK, MMAPLOCK or IOLOCK but no combination! So if we reach this 3rd condition we already know that the flags for ILOCK and MMAPLOCK were not set. However if there's possibility for more locks to be added in the future or just for the 'code symmetry' purposes - I have no problem to update the code.
>
>
Fair point. I do tend to agree with Darrick that I'd rather not rely on
even mildly tricky/subtle logic to optimize away things like asserts
(that are already optimized away on production kernels). Somebody could
come along, refactor this function and very easily gloss over the fact
that particular checks are missing. That said, I suppose it's
technically dead code with the current logic so it's not that big of a
deal IMO.
Brian
