linux-kernel - Re: [PATCH] f2fs: check sit bitmap under sentry

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Date:   Wed, 15 Nov 2017 20:33:34 +0800
From:   Chao Yu <chao@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>, jaegeuk@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: check sit bitmap under sentry_lock

Hi Jaegeuk,

Please drop this patch first, as it still can trigger deadlock as below, sorry
about this mistake.

- f2fs_put_super
 - f2fs_wait_discard_bios
  - __issue_discard_cmd
   - lock(&dcc->cmd_lock);		A
   - __check_sit_bitmap
    - down_read(&sit_i->sentry_lock)	B

- do_write_page
 - allocate_data_block
  - down_write(&sit_i->sentry_lock)	B
  - locate_dirty_segment
   - lock(&dirty_i->seglist_lock)	C

- write_checkpoint
 - clear_prefree_segments
  - lock(&dirty_i->seglist_lock)	C
   - f2fs_issue_discard
    - __issue_discard_async
     - __queue_discard_cmd
      - __update_discard_tree_range
       - lock(&dcc->cmd_lock)		A

Thanks,

On 2017/11/13 17:54, Chao Yu wrote:
> This patch protects sit bitmap accessing in __check_sit_bitmap with
> sentry_lock, meanwhile, in allocate_data_block, f2fs_wait_discard_bio
> will not access/update sit cache, let's exclude it from sentry_lock's
> region.>
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/segment.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index c117e0913f2a..464696b1612a 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -894,6 +894,8 @@ void __check_sit_bitmap(struct f2fs_sb_info *sbi,
>  	unsigned long offset, size, max_blocks = sbi->blocks_per_seg;
>  	unsigned long *map;
>  
> +	down_read(&SIT_I(sbi)->sentry_lock);
> +
>  	while (blk < end) {
>  		segno = GET_SEGNO(sbi, blk);
>  		sentry = get_seg_entry(sbi, segno);
> @@ -908,6 +910,8 @@ void __check_sit_bitmap(struct f2fs_sb_info *sbi,
>  		f2fs_bug_on(sbi, offset != size);
>  		blk = START_BLOCK(sbi, segno + 1);
>  	}
> +
> +	up_read(&SIT_I(sbi)->sentry_lock);
>  #endif
>  }
>  
> @@ -2527,12 +2531,13 @@ void allocate_data_block(struct f2fs_sb_info *sbi, struct page *page,
>  	down_read(&SM_I(sbi)->curseg_lock);
>  
>  	mutex_lock(&curseg->curseg_mutex);
> -	down_write(&sit_i->sentry_lock);
>  
>  	*new_blkaddr = NEXT_FREE_BLKADDR(sbi, curseg);
>  
>  	f2fs_wait_discard_bio(sbi, *new_blkaddr);
>  
> +	down_write(&sit_i->sentry_lock);
> +
>  	/*
>  	 * __add_sum_entry should be resided under the curseg_mutex
>  	 * because, this function updates a summary entry in the
>