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?
>
> Fixes: f847c699cff3 ("f2fs: allow out-place-update for direct IO in LFS mode")
> Signed-off-by: Chao Yu <c...@kernel.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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