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 force read to buffered
IO, 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>
---
fs/f2fs/file.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 278573974db4..866f1a34e92b 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -882,6 +882,10 @@ static bool f2fs_force_buffered_io(struct inode *inode,
int rw)
return true;
if (is_sbi_flag_set(sbi, SBI_CP_DISABLED))
return true;
+ /* In LFS mode, if there is inflight dio, force read to buffered IO */
+ if (rw == READ && f2fs_lfs_mode(sbi) &&
+ atomic_read(&inode->i_dio_count))
+ return false;
return false;
}
--
2.40.1
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