[PATCH 1/6] xfs: move the dio write relocking out of xfs_ilock_for_iomap

Christoph Hellwig
2024-06-19T11:54:32Z

About half of xfs_ilock_for_iomap deals with a special case for direct
I/O writes to COW files that need to take the ilock exclusively. Move
this code into the one callers that cares and simplify
xfs_ilock_for_iomap.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/xfs/xfs_iomap.c | 71 ++++++++++++++++++++++------------------------
1 file changed, 34 insertions(+), 37 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 3783426739258c..b0085e5972393a 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -717,53 +717,30 @@ imap_needs_cow(
return true;
}

+/*
+ * Extents not yet cached requires exclusive access, don't block for
+ * IOMAP_NOWAIT.
+ *
+ * This is basically an opencoded xfs_ilock_data_map_shared() call, but with
+ * support for IOMAP_NOWAIT.
+ */
static int
xfs_ilock_for_iomap(
struct xfs_inode *ip,
unsigned flags,
unsigned *lockmode)
{
- unsigned int mode = *lockmode;
- bool is_write = flags & (IOMAP_WRITE | IOMAP_ZERO);
-
- /*
- * 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_cow_inode(ip) && is_write)
- mode = XFS_ILOCK_EXCL;
-
- /*
- * Extents not yet cached requires exclusive access, don't block. This
- * is an opencoded xfs_ilock_data_map_shared() call but with
- * non-blocking behaviour.
- */
- if (xfs_need_iread_extents(&ip->i_df)) {
- if (flags & IOMAP_NOWAIT)
- return -EAGAIN;
- mode = XFS_ILOCK_EXCL;
- }
-
-relock:
if (flags & IOMAP_NOWAIT) {
- if (!xfs_ilock_nowait(ip, mode))
+ if (xfs_need_iread_extents(&ip->i_df))
+ return -EAGAIN;
+ if (!xfs_ilock_nowait(ip, *lockmode))
return -EAGAIN;
} else {
- xfs_ilock(ip, mode);
+ if (xfs_need_iread_extents(&ip->i_df))
+ *lockmode = XFS_ILOCK_EXCL;
+ xfs_ilock(ip, *lockmode);
}

- /*
- * The reflink iflag could have changed since the earlier unlocked
- * check, so if we got ILOCK_SHARED for a write and but we're now a
- * reflink inode we have to switch to ILOCK_EXCL and relock.
- */
- if (mode == XFS_ILOCK_SHARED && is_write && xfs_is_cow_inode(ip)) {
- xfs_iunlock(ip, mode);
- mode = XFS_ILOCK_EXCL;
- goto relock;
- }
-
- *lockmode = mode;
return 0;
}

@@ -801,7 +778,7 @@ xfs_direct_write_iomap_begin(
int nimaps = 1, error = 0;
bool shared = false;
u16 iomap_flags = 0;
- unsigned int lockmode = XFS_ILOCK_SHARED;
+ unsigned int lockmode;
u64 seq;

ASSERT(flags & (IOMAP_WRITE | IOMAP_ZERO));
@@ -817,10 +794,30 @@ xfs_direct_write_iomap_begin(
if (offset + length > i_size_read(inode))
iomap_flags |= IOMAP_F_DIRTY;

+ /*
+ * 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_cow_inode(ip))
+ lockmode = XFS_ILOCK_EXCL;
+ else
+ lockmode = XFS_ILOCK_SHARED;
+
+relock:
error = xfs_ilock_for_iomap(ip, flags, &lockmode);
if (error)
return error;

+ /*
+ * The reflink iflag could have changed since the earlier unlocked
+ * check, check if it again and relock if needed.
+ */
+ if (xfs_is_cow_inode(ip) && lockmode == XFS_ILOCK_SHARED) {
+ xfs_iunlock(ip, lockmode);
+ lockmode = XFS_ILOCK_EXCL;
+ goto relock;
+ }
+
error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
&nimaps, 0);
if (error)
--
2.43.0