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 <c...@kernel.org>
---
v3:
- wait for direct IO's completion before read IO.
fs/f2fs/file.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 9e171e138943..76a6043caf27 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -4608,6 +4608,10 @@ 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 {
--
2.40.1
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