linux-kernel - Re: [PATCH] f2fs: fix deadlock when flush inline data

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Date:	Wed, 11 May 2016 09:42:22 -0700
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Chao Yu <yuchao0@...wei.com>
Cc:	linux-f2fs-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: fix deadlock when flush inline data

Hi Chao,

On Wed, May 11, 2016 at 07:48:44PM +0800, Chao Yu wrote:
> Below backtrace info was reported by Yunlei He:
> 
> Call Trace:
>  [<ffffffff817a9395>] schedule+0x35/0x80
>  [<ffffffff817abb7d>] rwsem_down_read_failed+0xed/0x130
>  [<ffffffff813c12a8>] call_rwsem_down_read_failed+0x18/0x
>  [<ffffffff817ab1d0>] down_read+0x20/0x30
>  [<ffffffffa02a1a12>] f2fs_evict_inode+0x242/0x3a0 [f2fs]
>  [<ffffffff81217057>] evict+0xc7/0x1a0
>  [<ffffffff81217cd6>] iput+0x196/0x200
>  [<ffffffff812134f9>] __dentry_kill+0x179/0x1e0
>  [<ffffffff812136f9>] dput+0x199/0x1f0
>  [<ffffffff811fe77b>] __fput+0x18b/0x220
>  [<ffffffff811fe84e>] ____fput+0xe/0x10
>  [<ffffffff81097427>] task_work_run+0x77/0x90
>  [<ffffffff81074d62>] exit_to_usermode_loop+0x73/0xa2
>  [<ffffffff81003b7a>] do_syscall_64+0xfa/0x110
>  [<ffffffff817acf65>] entry_SYSCALL64_slow_path+0x25/0x25
> 
> Call Trace:
>  [<ffffffff817a9395>] schedule+0x35/0x80
>  [<ffffffff81216dc3>] __wait_on_freeing_inode+0xa3/0xd0
>  [<ffffffff810bc300>] ? autoremove_wake_function+0x40/0x4
>  [<ffffffff8121771d>] find_inode_fast+0x7d/0xb0
>  [<ffffffff8121794a>] ilookup+0x6a/0xd0
>  [<ffffffffa02bc740>] sync_node_pages+0x210/0x650 [f2fs]
>  [<ffffffff8122e690>] ? do_fsync+0x70/0x70
>  [<ffffffffa02b085e>] block_operations+0x9e/0xf0 [f2fs]
>  [<ffffffff8137b795>] ? bio_endio+0x55/0x60
>  [<ffffffffa02b0942>] write_checkpoint+0x92/0xba0 [f2fs]
>  [<ffffffff8117da57>] ? mempool_free_slab+0x17/0x20
>  [<ffffffff8117de8b>] ? mempool_free+0x2b/0x80
>  [<ffffffff8122e690>] ? do_fsync+0x70/0x70
>  [<ffffffffa02a53e3>] f2fs_sync_fs+0x63/0xd0 [f2fs]
>  [<ffffffff8129630f>] ? ext4_sync_fs+0xbf/0x190
>  [<ffffffff8122e6b0>] sync_fs_one_sb+0x20/0x30
>  [<ffffffff812002e9>] iterate_supers+0xb9/0x110
>  [<ffffffff8122e7b5>] sys_sync+0x55/0x90
>  [<ffffffff81003ae9>] do_syscall_64+0x69/0x110
>  [<ffffffff817acf65>] entry_SYSCALL64_slow_path+0x25/0x25
> 
> With following excuting serials, we will set inline_node in inode page
> after inode was unlinked, result in a deadloop described as below:
> 1. open file
> 2. write file
> 3. unlink file
> 4. write file
> 5. close file

Oh, I also tried this scenario before, but it seems I missed something.
I've seen writepages() was called to clear the flag between #4 and #5, but
it seems there was a timing difference.
Anyway, I could reproduce this and confirm that this patch fixed the issue. :)

Thanks,

> 
> Thread A				Thread B
>  - dput
>   - iput_final
>    - inode->i_state |= I_FREEING
>    - evict
>     - f2fs_evict_inode
> 					 - f2fs_sync_fs
> 					  - write_checkpoint
> 					   - block_operations
> 					    - f2fs_lock_all (down_write(cp_rwsem))
>      - f2fs_lock_op (down_read(cp_rwsem))
> 					    - sync_node_pages
> 					     - ilookup
> 					      - find_inode_fast
> 					       - __wait_on_freeing_inode
> 					         (wait on I_FREEING clear)
> 
> Here, we change to set inline_node flag only for linked inode for fixing.
> 
> Reported-by: Yunlei He <heyunlei@...wei.com>
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/data.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index eb6ce31..7805736 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1544,7 +1544,8 @@ restart:
>  		if (pos + len <= MAX_INLINE_DATA) {
>  			read_inline_data(page, ipage);
>  			set_inode_flag(F2FS_I(inode), FI_DATA_EXIST);
> -			set_inline_node(ipage);
> +			if (inode->i_nlink)
> +				set_inline_node(ipage);
>  		} else {
>  			err = f2fs_convert_inline_page(&dn, page);
>  			if (err)
> -- 
> 2.8.2.311.gee88674