1 files changed, 30 insertions, 12 deletions

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 66e1edbfb2b2..046469fcc1b8 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -955,15 +955,29 @@ static inline bool imap_needs_alloc(struct inode *inode,
                 (IS_DAX(inode) && imap->br_state == XFS_EXT_UNWRITTEN);
 }
 
+static inline bool needs_cow_for_zeroing(struct xfs_bmbt_irec *imap, int nimaps)
+{
+        return nimaps &&
+                imap->br_startblock != HOLESTARTBLOCK &&
+                imap->br_state != XFS_EXT_UNWRITTEN;
+}
+
 static inline bool need_excl_ilock(struct xfs_inode *ip, unsigned flags)
 {
         /*
-         * COW writes will allocate delalloc space, so we need to make sure
-         * to take the lock exclusively here.
+         * COW writes may allocate delalloc space or convert unwritten COW
+         * extents, so we need to make sure to take the lock exclusively here.
          */
         if (xfs_is_reflink_inode(ip) && (flags & (IOMAP_WRITE | IOMAP_ZERO)))
                 return true;
-        if ((flags & IOMAP_DIRECT) && (flags & IOMAP_WRITE))
+
+        /*
+         * 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;
 }
@@ -993,16 +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);
@@ -1024,7 +1040,9 @@ xfs_file_iomap_begin(
                         goto out_unlock;
         }
 
-        if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) {
+        if (xfs_is_reflink_inode(ip) &&
+            ((flags & IOMAP_WRITE) ||
+             ((flags & IOMAP_ZERO) && needs_cow_for_zeroing(&imap, nimaps)))) {
                 if (flags & IOMAP_DIRECT) {
                         /*
                          * A reflinked inode will result in CoW alloc.