On 2024/5/15 16:32, Wu Bo wrote:
On Fri, May 10, 2024 at 10:39:06AM +0800, Chao Yu wrote:
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
Looks like every COW filesystem would meet this situation. What's the solution
of other FS?
I missed to reply this...
Other cow filesystem like btrfs, it will update metadata after data IO
completion,
so it is safe.
Thanks,
This patch introduces a new per-inode i_opu_rwsem lock to avoid
such race condition.
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