Re: [PATCH v3] f2fs: fix to avoid data update racing between GC and DIO

[Jaegeuk Kim <jaegeuk@kernel.org>]

Hi Chao,

Could you take a look at this in xfstests/generic/013?

[  502.480850] ======================================================
[  502.480864] [ INFO: possible circular locking dependency detected ]
[  502.480877] 4.7.0-rc1+ #124 Tainted: G           OE  
[  502.480886] -------------------------------------------------------
[  502.480897] fsstress/10729 is trying to acquire lock:
[  502.480906]  (&sb->s_type->i_mutex_key#18){+.+.+.}, at: [<ffffffff81299c3b>] do_blockdev_direct_IO+0x1db/0x2310
[  502.480948] 
[  502.480948] but task is already holding lock:
[  502.480959]  (&fi->dio_rwsem){.+.+.+}, at: [<ffffffffc081e2b1>] f2fs_direct_IO+0xd1/0x3d0 [f2fs]
[  502.481003] 
[  502.481003] which lock already depends on the new lock.
[  502.481003] 
[  502.481018] 
[  502.481018] the existing dependency chain (in reverse order) is:
[  502.481030] 
[  502.481030] -> #1 (&fi->dio_rwsem){.+.+.+}:
[  502.481054]        [<ffffffff810e51c3>] lock_acquire+0xd3/0x220
[  502.481071]        [<ffffffff818d1921>] down_read+0x51/0xa0
[  502.481089]        [<ffffffffc081e2b1>] f2fs_direct_IO+0xd1/0x3d0 [f2fs]
[  502.481114]        [<ffffffff811c34c7>] generic_file_direct_write+0xa7/0x160
[  502.481133]        [<ffffffff811c363d>] __generic_file_write_iter+0xbd/0x1e0
[  502.481149]        [<ffffffffc080437b>] f2fs_file_write_iter+0xdb/0x100 [f2fs]
[  502.481173]        [<ffffffff81253a88>] __vfs_write+0xc8/0x140
[  502.481190]        [<ffffffff81254c55>] vfs_write+0xb5/0x1b0
[  502.481205]        [<ffffffff81255fe9>] SyS_write+0x49/0xa0
[  502.481220]        [<ffffffff818d4100>] entry_SYSCALL_64_fastpath+0x23/0xc1
[  502.481236] 
[  502.481236] -> #0 (&sb->s_type->i_mutex_key#18){+.+.+.}:
[  502.481264]        [<ffffffff810e481c>] __lock_acquire+0x161c/0x1940
[  502.481280]        [<ffffffff810e51c3>] lock_acquire+0xd3/0x220
[  502.481296]        [<ffffffff818d1b9a>] down_write+0x5a/0xc0
[  502.481312]        [<ffffffff81299c3b>] do_blockdev_direct_IO+0x1db/0x2310
[  502.481328]        [<ffffffff8129bdaa>] __blockdev_direct_IO+0x3a/0x40
[  502.481344]        [<ffffffffc081e2e4>] f2fs_direct_IO+0x104/0x3d0 [f2fs]
[  502.481368]        [<ffffffff811c40a9>] generic_file_read_iter+0x689/0x7e0
[  502.481384]        [<ffffffff812545d1>] __vfs_read+0xc1/0x130
[  502.481399]        [<ffffffff81254af1>] vfs_read+0x91/0x140
[  502.481414]        [<ffffffff81255f49>] SyS_read+0x49/0xa0
[  502.481429]        [<ffffffff818d4100>] entry_SYSCALL_64_fastpath+0x23/0xc1
[  502.481445] 
[  502.481445] other info that might help us debug this:
[  502.481445] 
[  502.481459]  Possible unsafe locking scenario:
[  502.481459] 
[  502.481726]        CPU0                    CPU1
[  502.481987]        ----                    ----
[  502.482242]   lock(&fi->dio_rwsem);
[  502.482501]                                lock(&sb->s_type->i_mutex_key#18);
[  502.482765]                                lock(&fi->dio_rwsem);
[  502.483025]   lock(&sb->s_type->i_mutex_key#18);
[  502.483285] 
[  502.483285]  *** DEADLOCK ***
[  502.483285] 
[  502.484018] 1 lock held by fsstress/10729:
[  502.484262]  #0:  (&fi->dio_rwsem){.+.+.+}, at: [<ffffffffc081e2b1>] f2fs_direct_IO+0xd1/0x3d0 [f2fs]

Thanks,

On Thu, Jul 07, 2016 at 12:49:12PM +0800, Chao Yu wrote:
> From: Chao Yu <yuchao0@huawei.com>
> 
> Datas in file can be operated by GC and DIO simultaneously, so we will
> face race case as below:
> 
> For write case:
> Thread A				Thread B
> - generic_file_direct_write
>  - invalidate_inode_pages2_range
>  - f2fs_direct_IO
>   - do_blockdev_direct_IO
>    - do_direct_IO
>     - get_more_blocks
> 					- f2fs_gc
> 					 - do_garbage_collect
> 					  - gc_data_segment
> 					   - move_data_page
> 					    - do_write_data_page
> 					    migrate data block to new block address
>    - dio_bio_submit
>    update user data to old block address
> 
> For read case:
> Thread A                                Thread B
> - generic_file_direct_write
>  - invalidate_inode_pages2_range
>  - f2fs_direct_IO
>   - do_blockdev_direct_IO
>    - do_direct_IO
>     - get_more_blocks
> 					- f2fs_balance_fs
> 					 - f2fs_gc
> 					  - do_garbage_collect
> 					   - gc_data_segment
> 					    - move_data_page
> 					     - do_write_data_page
> 					     migrate data block to new block address
> 					  - write_checkpoint
> 					   - do_checkpoint
> 					    - clear_prefree_segments
> 					     - f2fs_issue_discard
>                                              discard old block adress
>    - dio_bio_submit
>    update user buffer from obsolete block address
> 
> In order to fix this, for one file, we should let DIO and GC getting exclusion
> against with each other.
> 
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> ---
> v3: use semaphore to avoid racing in between read dio and write dio.
>  fs/f2fs/data.c  |  4 ++++
>  fs/f2fs/f2fs.h  |  1 +
>  fs/f2fs/gc.c    | 13 +++++++++++++
>  fs/f2fs/super.c |  1 +
>  4 files changed, 19 insertions(+)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index b6fd5bd..19197bb 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1712,6 +1712,7 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>  {
>  	struct address_space *mapping = iocb->ki_filp->f_mapping;
>  	struct inode *inode = mapping->host;
> +	struct f2fs_inode_info *fi = F2FS_I(inode);
>  	size_t count = iov_iter_count(iter);
>  	loff_t offset = iocb->ki_pos;
>  	int err;
> @@ -1727,7 +1728,10 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>  
>  	trace_f2fs_direct_IO_enter(inode, offset, count, iov_iter_rw(iter));
>  
> +	down_read(&fi->dio_rwsem);
>  	err = blockdev_direct_IO(iocb, inode, iter, get_data_block_dio);
> +	up_read(&fi->dio_rwsem);
> +
>  	if (iov_iter_rw(iter) == WRITE) {
>  		if (err > 0)
>  			set_inode_flag(inode, FI_UPDATE_WRITE);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index bf9a13a..2e439ec 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -474,6 +474,7 @@ struct f2fs_inode_info {
>  	struct list_head inmem_pages;	/* inmemory pages managed by f2fs */
>  	struct mutex inmem_lock;	/* lock for inmemory pages */
>  	struct extent_tree *extent_tree;	/* cached extent_tree entry */
> +	struct rw_semaphore dio_rwsem;	/* avoid racing between dio and gc */
>  };
>  
>  static inline void get_extent_info(struct extent_info *ext,
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index c612137..a9bfb8d 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -755,12 +755,25 @@ next_step:
>  		/* phase 3 */
>  		inode = find_gc_inode(gc_list, dni.ino);
>  		if (inode) {
> +			struct f2fs_inode_info *fi = F2FS_I(inode);
> +			bool locked = false;
> +
> +			if (S_ISREG(inode->i_mode)) {
> +				if (!down_write_trylock(&fi->dio_rwsem))
> +					continue;
> +				locked = true;
> +			}
> +
>  			start_bidx = start_bidx_of_node(nofs, inode)
>  								+ ofs_in_node;
>  			if (f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode))
>  				move_encrypted_block(inode, start_bidx);
>  			else
>  				move_data_page(inode, start_bidx, gc_type);
> +
> +			if (locked)
> +				up_write(&fi->dio_rwsem);
> +
>  			stat_inc_data_blk_count(sbi, 1, gc_type);
>  		}
>  	}
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index edd1b35..dde57fb 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -579,6 +579,7 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
>  	INIT_LIST_HEAD(&fi->gdirty_list);
>  	INIT_LIST_HEAD(&fi->inmem_pages);
>  	mutex_init(&fi->inmem_lock);
> +	init_rwsem(&fi->dio_rwsem);
>  
>  	/* Will be used by directory only */
>  	fi->i_dir_level = F2FS_SB(sb)->dir_level;
> -- 
> 2.7.2

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