[PATCH v4 1/6] ext4: prevent sleeping allocation in NOWAIT write path

[Baokun Li <libaokun@linux.alibaba.com>]

Block allocation requires journal access which may sleep, violating
NOWAIT semantics. Return -EAGAIN early when IOMAP_NOWAIT is set,
allowing the caller to retry without the NOWAIT constraint.

This ensures that write paths using IOMAP_NOWAIT (e.g., DIO with
RWF_NOWAIT) will not block on journal operations when blocks need
to be allocated.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260611163441.2431805-1-libaokun@linux.alibaba.com?part=1
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Baokun Li <libaokun@linux.alibaba.com>
---
 fs/ext4/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c2c2d6ac7f3d..832794294ccf 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3672,6 +3672,9 @@ static int ext4_iomap_alloc(struct inode *inode, struct ext4_map_blocks *map,
 	int ret, dio_credits, m_flags = 0, retries = 0;
 	bool force_commit = false;
 
+	if (flags & IOMAP_NOWAIT)
+		return -EAGAIN;
+
 	/*
 	 * Trim the mapping request to the maximum value that we can map at
 	 * once for direct I/O.
-- 
2.43.7