Re: [PATCH v11 1/4] xfs: Refactor xfs_isilocked()

[Brian Foster <bfoster@redhat.com>]

On Wed, Oct 14, 2020 at 11:04:31PM +0200, Pavel Reichl wrote:
> 
> 
> On 10/12/20 6:03 PM, Brian Foster wrote:
> > On Fri, Oct 09, 2020 at 09:55:12PM +0200, 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@redhat.com>
> >> Suggested-by: Dave Chinner <dchinner@redhat.com>
> >> Suggested-by: Eric Sandeen <sandeen@redhat.com>
> >> Suggested-by: Darrick J. Wong <darrick.wong@oracle.com>
> >> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> >> ---
> >>  fs/xfs/xfs_inode.c | 48 ++++++++++++++++++++++++++++++++++++++--------
> >>  fs/xfs/xfs_inode.h | 21 +++++++++++++-------
> >>  2 files changed, 54 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> >> index c06129cffba9..7c1ceb4df4ec 100644
> >> --- a/fs/xfs/xfs_inode.c
> >> +++ b/fs/xfs/xfs_inode.c
> >> @@ -345,9 +345,43 @@ xfs_ilock_demote(
> >>  }
> >>  
> >>  #if defined(DEBUG) || defined(XFS_WARN)
> >> -int
> >> +static inline bool
> >> +__xfs_rwsem_islocked(
> >> +	struct rw_semaphore	*rwsem,
> >> +	int			lock_flags)
> >> +{
> >> +	int			arg;
> >> +
> >> +	if (!debug_locks)
> >> +		return rwsem_is_locked(rwsem);
> >> +
> >> +	if (lock_flags & (1 << XFS_SHARED_LOCK_SHIFT)) {
> >> +		/*
> >> +		 * The caller could be asking if we have (shared | excl)
> >> +		 * access to the lock. Ask lockdep if the rwsem is
> >> +		 * locked either for read or write access.
> >> +		 *
> >> +		 * The caller could also be asking if we have only
> >> +		 * shared access to the lock. Holding a rwsem
> >> +		 * write-locked implies read access as well, so the
> >> +		 * request to lockdep is the same for this case.
> >> +		 */
> >> +		arg = -1;
> >> +	} else {
> >> +		/*
> >> +		 * The caller is asking if we have only exclusive access
> >> +		 * to the lock. Ask lockdep if the rwsem is locked for
> >> +		 * write access.
> >> +		 */
> >> +		arg = 0;
> >> +	}
> ...
> > 
> > Also, I find the pattern of shifting in the caller slightly confusing,
> > particularly with the 'lock_flags' name being passed down through the
> > caller. Any reason we couldn't pass the shift value as a parameter and
> > do the shift at the top of the function so the logic is clear and in one
> > place?
> > 
> 
> Hi Brian, is following change what you had in mind? Thanks!
> 

Yep, pretty much. I find shifted_lock_flags to be a little verbose as a
name. I'd be fine with just doing something like 'lock_flags >>= shift'
near the top of the function, but that's more of a personal nit. I also
like Christoph's suggestion to avoid the arg variable (along with the
comment update suggested in the discussion with Darrick).

Brian

> 
> >> @@ -349,14 +349,16 @@ xfs_ilock_demote(
>  static inline bool
>  __xfs_rwsem_islocked(
>  	struct rw_semaphore	*rwsem,
> -	int			lock_flags)
> +	int			lock_flags,
> +	int			shift)
>  {
>  	int			arg;
> +	const int		shifted_lock_flags = lock_flags >> shift;
>  
>  	if (!debug_locks)
>  		return rwsem_is_locked(rwsem);
>  
> -	if (lock_flags & (1 << XFS_SHARED_LOCK_SHIFT)) {
> +	if (shifted_lock_flags & (1 << XFS_SHARED_LOCK_SHIFT)) {
>  		/*
>  		 * The caller could be asking if we have (shared | excl)
>  		 * access to the lock. Ask lockdep if the rwsem is
> @@ -387,20 +389,20 @@ xfs_isilocked(
>  {
>  	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));
> +		return __xfs_rwsem_islocked(&ip->i_lock, lock_flags,
> +				XFS_ILOCK_FLAG_SHIFT);
>  	}
>  
>  	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));
> +		return __xfs_rwsem_islocked(&ip->i_mmaplock, lock_flags,
> +				XFS_MMAPLOCK_FLAG_SHIFT);
>  	}
>  
>  	if (lock_flags & (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED)) {
> -		return __xfs_rwsem_islocked(&VFS_I(ip)->i_rwsem,
> -				(lock_flags >> XFS_IOLOCK_FLAG_SHIFT));
> +		return __xfs_rwsem_islocked(&VFS_I(ip)->i_rwsem, lock_flags,
> +				XFS_IOLOCK_FLAG_SHIFT);
>  	}
>  
>  	ASSERT(0);
>