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Date: Wed, 15 May 2024 09:42:20 +0800
From: Chao Yu <chao@...nel.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: fix to avoid racing in between read and OPU dio
write
On 2024/5/15 0:09, Jaegeuk Kim wrote:
> On 05/10, 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
>>
>> This patch introduces a new per-inode i_opu_rwsem lock to avoid
>> such race condition.
>
> Wasn't this supposed to be managed by user-land?
Actually, the test case is:
1. mount w/ lfs mode
2. touch file;
3. initialize file w/ 4k zeroed data; fsync;
4. continue triggering dio write 4k zeroed data to file;
5. and meanwhile, continue triggering buf/dio 4k read in file,
use md5sum to verify the 4k data;
It expects data is all zero, however it turned out it's not.
Thanks,
>
>>
>> Fixes: f847c699cff3 ("f2fs: allow out-place-update for direct IO in LFS mode")
>> Signed-off-by: Chao Yu <chao@...nel.org>
>> ---
>> v2:
>> - fix to cover dio read path w/ i_opu_rwsem as well.
>> fs/f2fs/f2fs.h | 1 +
>> fs/f2fs/file.c | 28 ++++++++++++++++++++++++++--
>> fs/f2fs/super.c | 1 +
>> 3 files changed, 28 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 30058e16a5d0..91cf4b3d6bc6 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -847,6 +847,7 @@ struct f2fs_inode_info {
>> /* avoid racing between foreground op and gc */
>> struct f2fs_rwsem i_gc_rwsem[2];
>> struct f2fs_rwsem i_xattr_sem; /* avoid racing between reading and changing EAs */
>> + struct f2fs_rwsem i_opu_rwsem; /* avoid racing between buf read and opu dio write */
>>
>> int i_extra_isize; /* size of extra space located in i_addr */
>> kprojid_t i_projid; /* id for project quota */
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index 72ce1a522fb2..4ec260af321f 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -4445,6 +4445,7 @@ static ssize_t f2fs_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
>> const loff_t pos = iocb->ki_pos;
>> const size_t count = iov_iter_count(to);
>> struct iomap_dio *dio;
>> + bool do_opu = f2fs_lfs_mode(sbi);
>> ssize_t ret;
>>
>> if (count == 0)
>> @@ -4457,8 +4458,14 @@ static ssize_t f2fs_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
>> ret = -EAGAIN;
>> goto out;
>> }
>> + if (do_opu && !f2fs_down_read_trylock(&fi->i_opu_rwsem)) {
>> + f2fs_up_read(&fi->i_gc_rwsem[READ]);
>> + ret = -EAGAIN;
>> + goto out;
>> + }
>> } else {
>> f2fs_down_read(&fi->i_gc_rwsem[READ]);
>> + f2fs_down_read(&fi->i_opu_rwsem);
>> }
>>
>> /*
>> @@ -4477,6 +4484,7 @@ static ssize_t f2fs_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
>> ret = iomap_dio_complete(dio);
>> }
>>
>> + f2fs_up_read(&fi->i_opu_rwsem);
>> f2fs_up_read(&fi->i_gc_rwsem[READ]);
>>
>> file_accessed(file);
>> @@ -4523,7 +4531,13 @@ static ssize_t f2fs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
>> if (f2fs_should_use_dio(inode, iocb, to)) {
>> ret = f2fs_dio_read_iter(iocb, to);
>> } else {
>> + bool do_opu = f2fs_lfs_mode(F2FS_I_SB(inode));
>> +
>> + if (do_opu)
>> + f2fs_down_read(&F2FS_I(inode)->i_opu_rwsem);
>> ret = filemap_read(iocb, to, 0);
>> + if (do_opu)
>> + f2fs_up_read(&F2FS_I(inode)->i_opu_rwsem);
>> if (ret > 0)
>> f2fs_update_iostat(F2FS_I_SB(inode), inode,
>> APP_BUFFERED_READ_IO, ret);
>> @@ -4748,14 +4762,22 @@ static ssize_t f2fs_dio_write_iter(struct kiocb *iocb, struct iov_iter *from,
>> ret = -EAGAIN;
>> goto out;
>> }
>> + if (do_opu && !f2fs_down_write_trylock(&fi->i_opu_rwsem)) {
>> + f2fs_up_read(&fi->i_gc_rwsem[READ]);
>> + f2fs_up_read(&fi->i_gc_rwsem[WRITE]);
>> + ret = -EAGAIN;
>> + goto out;
>> + }
>> } else {
>> ret = f2fs_convert_inline_inode(inode);
>> if (ret)
>> goto out;
>>
>> f2fs_down_read(&fi->i_gc_rwsem[WRITE]);
>> - if (do_opu)
>> + if (do_opu) {
>> f2fs_down_read(&fi->i_gc_rwsem[READ]);
>> + f2fs_down_write(&fi->i_opu_rwsem);
>> + }
>> }
>>
>> /*
>> @@ -4779,8 +4801,10 @@ static ssize_t f2fs_dio_write_iter(struct kiocb *iocb, struct iov_iter *from,
>> ret = iomap_dio_complete(dio);
>> }
>>
>> - if (do_opu)
>> + if (do_opu) {
>> + f2fs_up_write(&fi->i_opu_rwsem);
>> f2fs_up_read(&fi->i_gc_rwsem[READ]);
>> + }
>> f2fs_up_read(&fi->i_gc_rwsem[WRITE]);
>>
>> if (ret < 0)
>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>> index daf2c4dbe150..b4ed3b094366 100644
>> --- a/fs/f2fs/super.c
>> +++ b/fs/f2fs/super.c
>> @@ -1428,6 +1428,7 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
>> init_f2fs_rwsem(&fi->i_gc_rwsem[READ]);
>> init_f2fs_rwsem(&fi->i_gc_rwsem[WRITE]);
>> init_f2fs_rwsem(&fi->i_xattr_sem);
>> + init_f2fs_rwsem(&fi->i_opu_rwsem);
>>
>> /* Will be used by directory only */
>> fi->i_dir_level = F2FS_SB(sb)->dir_level;
>> --
>> 2.40.1
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