6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chao Yu <chao@xxxxxxxxxx>
[ Upstream commit 0cac51185e65dc2a20686184e02f3cafc99eb202 ]
If lfs mode is on, buffered read may race w/ OPU dio write as below,
it may cause buffered read hits unwritten data unexpectly, and for
dio read, the race condition exists as well.
Thread A Thread B
- f2fs_file_write_iter
- f2fs_dio_write_iter
- __iomap_dio_rw
- f2fs_iomap_begin
- f2fs_map_blocks
- __allocate_data_block
- allocated blkaddr #x
- iomap_dio_submit_bio
- f2fs_file_read_iter
- filemap_read
- f2fs_read_data_folio
- f2fs_mpage_readpages
- f2fs_map_blocks
: get blkaddr #x
- f2fs_submit_read_bio
IRQ
- f2fs_read_end_io
: read IO on blkaddr #x complete
IRQ
- iomap_dio_bio_end_io
: direct write IO on blkaddr #x complete
In LFS mode, if there is inflight dio, let's wait for its completion,
this policy won't cover all race cases, however it is a tradeoff which
avoids abusing lock around IO paths.
Fixes: f847c699cff3 ("f2fs: allow out-place-update for direct IO in LFS mode")
Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/f2fs/file.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 81e342bd993c2..8c4c5c6c1ac64 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -4541,6 +4541,10 @@ static ssize_t f2fs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
f2fs_trace_rw_file_path(iocb->ki_filp, iocb->ki_pos,
iov_iter_count(to), READ);
+ /* In LFS mode, if there is inflight dio, wait for its completion */
+ if (f2fs_lfs_mode(F2FS_I_SB(inode)))
+ inode_dio_wait(inode);
+
if (f2fs_should_use_dio(inode, iocb, to)) {
ret = f2fs_dio_read_iter(iocb, to);
} else {
--
2.43.0
