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

[Brian Foster <bfoster@redhat.com>]

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;
> +	}

Are these arg values documented somewhere? A quick look at the function
below didn't show anything..

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?

> +
> +	return lockdep_is_held_type(rwsem, arg);
> +}
> +
> +bool
>  xfs_isilocked(
> -	xfs_inode_t		*ip,
> +	struct xfs_inode	*ip,
>  	uint			lock_flags)
>  {
>  	if (lock_flags & (XFS_ILOCK_EXCL|XFS_ILOCK_SHARED)) {
...
> diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
> index e9a8bb184d1f..77776af75c77 100644
> --- a/fs/xfs/xfs_inode.h
> +++ b/fs/xfs/xfs_inode.h
> @@ -268,12 +268,19 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
>   * Bit ranges:	1<<1  - 1<<16-1 -- iolock/ilock modes (bitfield)
>   *		1<<16 - 1<<32-1 -- lockdep annotation (integers)
>   */
> -#define	XFS_IOLOCK_EXCL		(1<<0)
> -#define	XFS_IOLOCK_SHARED	(1<<1)
> -#define	XFS_ILOCK_EXCL		(1<<2)
> -#define	XFS_ILOCK_SHARED	(1<<3)
> -#define	XFS_MMAPLOCK_EXCL	(1<<4)
> -#define	XFS_MMAPLOCK_SHARED	(1<<5)
> +
> +#define XFS_IOLOCK_FLAG_SHIFT	0
> +#define XFS_ILOCK_FLAG_SHIFT	2
> +#define XFS_MMAPLOCK_FLAG_SHIFT	4
> +
> +#define XFS_SHARED_LOCK_SHIFT	1
> +
> +#define XFS_IOLOCK_EXCL		(1 << (XFS_IOLOCK_FLAG_SHIFT))
> +#define XFS_IOLOCK_SHARED	(XFS_IOLOCK_EXCL << (XFS_SHARED_LOCK_SHIFT))
> +#define XFS_ILOCK_EXCL		(1 << (XFS_ILOCK_FLAG_SHIFT))
> +#define XFS_ILOCK_SHARED	(XFS_ILOCK_EXCL << (XFS_SHARED_LOCK_SHIFT))
> +#define XFS_MMAPLOCK_EXCL	(1 << (XFS_MMAPLOCK_FLAG_SHIFT))
> +#define XFS_MMAPLOCK_SHARED	(XFS_MMAPLOCK_EXCL << (XFS_SHARED_LOCK_SHIFT))
>  

Any reason for the extra params around the shift values?

Brian

>  #define XFS_LOCK_MASK		(XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED \
>  				| XFS_ILOCK_EXCL | XFS_ILOCK_SHARED \
> @@ -412,7 +419,7 @@ 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(struct xfs_inode *, uint);
>  uint		xfs_ilock_data_map_shared(struct xfs_inode *);
>  uint		xfs_ilock_attr_map_shared(struct xfs_inode *);
>  
> -- 
> 2.26.2
>