xfs: don't block on the ilock for RWF_NOWAIT

Fix xfs_file_iomap_begin to trylock the ilock if IOMAP_NOWAIT is passed,
so that we don't block io_submit callers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index ee01859..046469f 100644 (file)
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -970,6 +970,15 @@ static inline bool need_excl_ilock(struct xfs_inode *ip, unsigned flags)
         */
        if (xfs_is_reflink_inode(ip) && (flags & (IOMAP_WRITE | IOMAP_ZERO)))
                return true;
+
+       /*
+        * Extents not yet cached requires exclusive access, don't block.
+        * This is an opencoded xfs_ilock_data_map_shared() to cater for the
+        * non-blocking behaviour.
+        */
+       if (ip->i_d.di_format == XFS_DINODE_FMT_BTREE &&
+           !(ip->i_df.if_flags & XFS_IFEXTENTS))
+               return true;
        return false;
 }
 
@@ -998,16 +1007,18 @@ xfs_file_iomap_begin(
                return xfs_file_iomap_begin_delay(inode, offset, length, iomap);
        }
 
-       if (need_excl_ilock(ip, flags)) {
+       if (need_excl_ilock(ip, flags))
                lockmode = XFS_ILOCK_EXCL;
-               xfs_ilock(ip, XFS_ILOCK_EXCL);
-       } else {
-               lockmode = xfs_ilock_data_map_shared(ip);
-       }
+       else
+               lockmode = XFS_ILOCK_SHARED;
 
-       if ((flags & IOMAP_NOWAIT) && !(ip->i_df.if_flags & XFS_IFEXTENTS)) {
-               error = -EAGAIN;
-               goto out_unlock;
+       if (flags & IOMAP_NOWAIT) {
+               if (!(ip->i_df.if_flags & XFS_IFEXTENTS))
+                       return -EAGAIN;
+               if (!xfs_ilock_nowait(ip, lockmode))
+                       return -EAGAIN;
+       } else {
+               xfs_ilock(ip, lockmode);
        }
 
        ASSERT(offset <= mp->m_super->s_maxbytes);