linux-kernel - Re: [PATCH] f2fs: fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node

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Date:   Wed, 17 Jun 2020 20:28:16 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     <zhaowuyun@...gtech.com>, <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] f2fs: fix a race condition between f2fs_write_end_io and
 f2fs_del_fsync_node_entry

On 2020/6/17 17:04, zhaowuyun@...gtech.com wrote:
> From: Wuyun Zhao <zhaowuyun@...gtech.com>
> 
> Under some condition, the __write_node_page will submit a page which is not
> f2fs_in_warm_node_list and will not call f2fs_add_fsync_node_entry.
> f2fs_gc continue to run to invoke f2fs_iget -> do_read_inode to read the same node page
> and set code node, which make f2fs_in_warm_node_list become true,
> that will cause f2fs_bug_on in f2fs_del_fsync_node_entry when f2fs_write_end_io called.
Could you please add below race condition description into commit message?

- f2fs_write_end_io
					- f2fs_iget
					 - do_read_inode
					  - set_cold_node
					  recover cold node flag
 - f2fs_in_warm_node_list
  - is_cold_node
  if node is cold, assume we have added
  node to fsync_node_list during writepages()
 - f2fs_del_fsync_node_entry
  - f2fs_bug_on() due to node page
  is not in fsync_node_list

BTW, I'm curious about why we can lose cold flag for non-dir inode?
any clue to reproduce this bug (I mean losing cold flag)?

> 
> [   34.966133] Call trace:
> [   34.969902]  f2fs_del_fsync_node_entry+0x100/0x108
> [   34.976071]  f2fs_write_end_io+0x1e0/0x288
> [   34.981539]  bio_endio+0x248/0x270
> [   34.986289]  blk_update_request+0x2b0/0x4d8
> [   34.991841]  scsi_end_request+0x40/0x440
> [   34.997126]  scsi_io_completion+0xa4/0x748
> [   35.002593]  scsi_finish_command+0xdc/0x110
> [   35.008143]  scsi_softirq_done+0x118/0x150
> [   35.013610]  blk_done_softirq+0x8c/0xe8
> [   35.018811]  __do_softirq+0x2e8/0x578
> [   35.023828]  irq_exit+0xfc/0x120
> [   35.028398]  handle_IPI+0x1d8/0x330
> [   35.033233]  gic_handle_irq+0x110/0x1d4
> [   35.038433]  el1_irq+0xb4/0x130
> [   35.042917]  kmem_cache_alloc+0x3f0/0x418
> [   35.048288]  radix_tree_node_alloc+0x50/0xf8
> [   35.053933]  __radix_tree_create+0xf8/0x188
> [   35.059484]  __radix_tree_insert+0x3c/0x128
> [   35.065035]  add_gc_inode+0x90/0x118
> [   35.069967]  f2fs_gc+0x1b80/0x2d70
> [   35.074718]  f2fs_disable_checkpoint+0x94/0x1d0
> [   35.080621]  f2fs_fill_super+0x10c4/0x1b88
> [   35.086088]  mount_bdev+0x194/0x1e0
> [   35.090923]  f2fs_mount+0x40/0x50
> [   35.095589]  mount_fs+0xb4/0x190
> [   35.100159]  vfs_kern_mount+0x80/0x1d8
> [   35.105260]  do_mount+0x478/0xf18
> [   35.109926]  ksys_mount+0x90/0xd0
> [   35.114592]  __arm64_sys_mount+0x24/0x38
> 
> Signed-off-by: Wuyun Zhao <zhaowuyun@...gtech.com>

Reviewed-by: Chao Yu <yuchao0@...wei.com>

Thanks,

> ---
>  fs/f2fs/inode.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index be6ac33..0df5c8c 100644
> --- a/fs/f2fs/inode.c
> +++ b/fs/f2fs/inode.c
> @@ -402,6 +402,7 @@ static int do_read_inode(struct inode *inode)
>  
>  	/* try to recover cold bit for non-dir inode */
>  	if (!S_ISDIR(inode->i_mode) && !is_cold_node(node_page)) {
> +		f2fs_wait_on_page_writeback(node_page, NODE, true, true);
>  		set_cold_node(node_page, false);
>  		set_page_dirty(node_page);
>  	}
>