[PATCH] block: don't take i_rwsem twice in the direct write fallback

[Zhenxian Ma <mzx199711@gmail.com>]

commit 2fec4fd97cc3 ("block: take i_rwsem for the direct I/O write
fallback") takes i_rwsem around blkdev_buffered_write() in the direct
write fallback.  commit 1b1be9ea4e34 ("block: take the inode lock for
buffered write fallback") fixes the same race by taking i_rwsem inside
blkdev_buffered_write().  With both applied, the fallback takes i_rwsem
shared twice.

Drop the outer locking in the fallback.

Fixes: 1b1be9ea4e34 ("block: take the inode lock for buffered write fallback")
Reported-by: syzbot+bd975ef54294bec73f0e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=bd975ef54294bec73f0e
Cc: Tal Zussman <tz2294@columbia.edu>
Cc: Julian Sun <sunjunchao@bytedance.com>
Assisted-by: LLM
Signed-off-by: Zhenxian Ma <mzx199711@gmail.com>
---
 block/fops.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/block/fops.c b/block/fops.c
index 0e4c42c8b74f..ddab4940d76b 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -809,13 +809,8 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
 				else if (!blkdev_dio_fua(iocb, bdev))
 					need_sync = true;
 			} else {
-				ssize_t ret2;
-
-				inode_lock_shared(bd_inode);
-				ret2 = blkdev_buffered_write(iocb, from);
-				inode_unlock_shared(bd_inode);
 				ret = direct_write_fallback(iocb, from, ret,
-							    ret2);
+						blkdev_buffered_write(iocb, from));
 				need_sync = true;
 			}
 		} else if (ret > 0 && !blkdev_dio_fua(iocb, bdev)) {
-- 
2.39.3