linux-kernel - [PATCH] f2fs: Fix direct IO handling

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Message-Id: <20191126075719.1046485-1-damien.lemoal@wdc.com>
Date:   Tue, 26 Nov 2019 16:57:19 +0900
From:   Damien Le Moal <damien.lemoal@....com>
To:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Jaegeuk Kim <jaegeuk@...nel.org>,
        Chao Yu <yuchao0@...wei.com>
Cc:     linux-fsdevel@...r.kernel.org,
        Javier Gonzalez <javier@...igon.com>,
        Shinichiro Kawasaki <shinichiro.kawasaki@....com>
Subject: [PATCH] f2fs: Fix direct IO handling

f2fs_preallocate_blocks() identifies direct IOs using the IOCB_DIRECT
flag for a kiocb structure. However, the file system direct IO handler
function f2fs_direct_IO() may have decided that a direct IO has to be
exececuted as a buffered IO using the function f2fs_force_buffered_io().
This is the case for instance for volumes including zoned block device
and for unaligned write IOs with LFS mode enabled.

These 2 different methods of identifying direct IOs can result in
inconsistencies generating stale data access for direct reads after a
direct IO write that is treated as a buffered write. Fix this
inconsistency by combining the IOCB_DIRECT flag test with the result
of f2fs_force_buffered_io().

Reported-by: Javier Gonzalez <javier@...igon.com>
Signed-off-by: Damien Le Moal <damien.lemoal@....com>
---
 fs/f2fs/data.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 5755e897a5f0..8ac2d3b70022 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1073,6 +1073,8 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 	int flag;
 	int err = 0;
 	bool direct_io = iocb->ki_flags & IOCB_DIRECT;
+	bool do_direct_io = direct_io &&
+		!f2fs_force_buffered_io(inode, iocb, from);

 	/* convert inline data for Direct I/O*/
 	if (direct_io) {
@@ -1081,7 +1083,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 			return err;
 	}

-	if (direct_io && allow_outplace_dio(inode, iocb, from))
+	if (do_direct_io && allow_outplace_dio(inode, iocb, from))
 		return 0;

 	if (is_inode_flag_set(inode, FI_NO_PREALLOC))
-- 
2.23.0