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Date: Wed, 15 May 2024 04:42:58 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...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 05/15, Chao Yu wrote:
> 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.
Can we check outstanding write bios instead of abusing locks?
>
> 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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