[PATCH 1/5] filemap: drain in-flight DIO before buffered writes

[Jiale Yao]

An asynchronous direct write can remain in flight after its submitting
thread releases the inode lock. A buffered write can then dirty page
cache before the direct write completes its post-I/O invalidation. The
invalidation finds dirty pages, reports a possible data corruption, and
records -EIO in the mapping error sequence.

Drain in-flight DIO before both regular buffered writes and direct I/O
fallbacks in __generic_file_write_iter(). Preserve IOCB_NOWAIT semantics
by returning -EAGAIN when waiting would be required, while retaining a
positive partial direct write result.

Fixes: 8174202b34c3 ("write_iter variants of {__,}generic_file_aio_write()")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jiale Yao <yaojiale02@xxxxxxx>
---
 mm/filemap.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index b74bc1e5015c..289b8ca44ada 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4502,10 +4502,19 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		 */
 		if (ret < 0 || !iov_iter_count(from) || IS_DAX(inode))
 			return ret;
+		if ((iocb->ki_flags & IOCB_NOWAIT) &&
+		    atomic_read(&inode->i_dio_count))
+			return ret ?: -EAGAIN;
+		inode_dio_wait(inode);
 		return direct_write_fallback(iocb, from, ret,
 				generic_perform_write(iocb, from));
 	}
 
+	if ((iocb->ki_flags & IOCB_NOWAIT) &&
+	    atomic_read(&inode->i_dio_count))
+		return -EAGAIN;
+	inode_dio_wait(inode);
+
 	return generic_perform_write(iocb, from);
 }
 EXPORT_SYMBOL(__generic_file_write_iter);
-- 
2.34.1