On 2019/11/26 4:03, Javier González wrote: > On 25.11.2019 00:48, Damien Le Moal wrote: >> On 2019/11/22 18:00, Javier González wrote: >>> From: Javier González <[email protected]> >>> >>> Fix file system corruption when using LFS mount (e.g., in zoned >>> devices). Seems like the fallback into buffered I/O creates an >>> inconsistency if the application is assuming both read and write DIO. I >>> can easily reproduce a corruption with a simple RocksDB test. >>> >>> Might be that the f2fs_forced_buffered_io path brings some problems too, >>> but I have not seen other failures besides this one. >>> >>> Problem reproducible without a zoned block device, simply by forcing >>> LFS mount: >>> >>> $ sudo mkfs.f2fs -f -m /dev/nvme0n1 >>> $ sudo mount /dev/nvme0n1 /mnt/f2fs >>> $ sudo /opt/rocksdb/db_bench --benchmarks=fillseq --use_existing_db=0 >>> --use_direct_reads=true --use_direct_io_for_flush_and_compaction=true >>> --db=/mnt/f2fs --num=5000 --value_size=1048576 --verify_checksum=1 >>> --block_size=65536 >>> >>> Note that the options that cause the problem are: >>> --use_direct_reads=true --use_direct_io_for_flush_and_compaction=true >>> >>> Fixes: f9d6d0597698 ("f2fs: fix out-place-update DIO write") >>> >>> Signed-off-by: Javier González <[email protected]> >>> --- >>> fs/f2fs/data.c | 3 --- >>> 1 file changed, 3 deletions(-) >>> >>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c >>> index 5755e897a5f0..b045dd6ab632 100644 >>> --- a/fs/f2fs/data.c >>> +++ b/fs/f2fs/data.c >>> @@ -1081,9 +1081,6 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, >>> struct iov_iter *from) >>> return err; >>> } >>> >>> - if (direct_io && allow_outplace_dio(inode, iocb, from)) >>> - return 0; >> >> Since for LFS mode, all DIOs can end up out of place, I think that it >> may be better to change allow_outplace_dio() to always return true in >> the case of LFS mode. So may be something like: >> >> static inline int allow_outplace_dio(struct inode *inode, >> struct kiocb *iocb, struct iov_iter *iter) >> { >> struct f2fs_sb_info *sbi = F2FS_I_SB(inode); >> int rw = iov_iter_rw(iter); >> >> return test_opt(sbi, LFS) || >> (rw == WRITE && !block_unaligned_IO(inode, iocb, iter)); >> } >> >> instead of the original: >> >> static inline int allow_outplace_dio(struct inode *inode, >> struct kiocb *iocb, struct iov_iter *iter) >> { >> struct f2fs_sb_info *sbi = F2FS_I_SB(inode); >> int rw = iov_iter_rw(iter); >> >> return (test_opt(sbi, LFS) && (rw == WRITE) && >> !block_unaligned_IO(inode, iocb, iter)); >> } >> >> Thoughts ? >> > > I see what you mean and it makes sense. However, the problem I am seeing > occurs when allow_outplace_dio() returns true, as this is what creates > the inconsistency between the write being buffered and the read being > DIO.
But if the write is switched to buffered, the DIO read should use the buffered path too, no ? Since this is all happening under VFS, the generic DIO read path will not ensure that the buffered writes are flushed to disk before issuing the direct read, I think. So that would explain your data corruption, i.e. you are reading stale data on the device before the buffered writes make it to the media. > > I did test the code you propose and, as expected, it still triggered the > corruption. > >>> - >>> if (is_inode_flag_set(inode, FI_NO_PREALLOC)) >>> return 0; >>> >>> >> >> >> -- >> Damien Le Moal >> Western Digital Research > > Thanks, > Javier > -- Damien Le Moal Western Digital Research _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
