Date:   Thu, 16 Mar 2023 10:13:14 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Yonggil Song <yonggil.song@...sung.com>
Cc:     "chao@...nel.org" <chao@...nel.org>,
        "linux-f2fs-devel@...ts.sourceforge.net" 
        <linux-f2fs-devel@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] f2fs: Fix system crash due to lack of free space in
 LFS

On 03/14, Yonggil Song wrote:
> When f2fs tries to checkpoint during foreground gc in LFS mode, system
> crash occurs due to lack of free space if the amount of dirty node and
> dentry pages generated by data migration exceeds free space.
> The reproduction sequence is as follows.
> 
>  - 20GiB capacity block device (null_blk)
>  - format and mount with LFS mode
>  - create a file and write 20,000MiB
>  - 4k random write on full range of the file
> 
>  RIP: 0010:new_curseg+0x48a/0x510 [f2fs]
>  Code: 55 e7 f5 89 c0 48 0f af c3 48 8b 5d c0 48 c1 e8 20 83 c0 01 89 43 6c 48 83 c4 28 5b 41 5c 41 5d 41 5e 41 5f 5d c3 cc cc cc cc <0f> 0b f0 41 80 4f 48 04 45 85 f6 0f 84 ba fd ff ff e9 ef fe ff ff
>  RSP: 0018:ffff977bc397b218 EFLAGS: 00010246
>  RAX: 00000000000027b9 RBX: 0000000000000000 RCX: 00000000000027c0
>  RDX: 0000000000000000 RSI: 00000000000027b9 RDI: ffff8c25ab4e74f8
>  RBP: ffff977bc397b268 R08: 00000000000027b9 R09: ffff8c29e4a34b40
>  R10: 0000000000000001 R11: ffff977bc397b0d8 R12: 0000000000000000
>  R13: ffff8c25b4dd81a0 R14: 0000000000000000 R15: ffff8c2f667f9000
>  FS: 0000000000000000(0000) GS:ffff8c344ec80000(0000) knlGS:0000000000000000
>  CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 000000c00055d000 CR3: 0000000e30810003 CR4: 00000000003706e0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  Call Trace:
>  <TASK>
>  allocate_segment_by_default+0x9c/0x110 [f2fs]
>  f2fs_allocate_data_block+0x243/0xa30 [f2fs]
>  ? __mod_lruvec_page_state+0xa0/0x150
>  do_write_page+0x80/0x160 [f2fs]
>  f2fs_do_write_node_page+0x32/0x50 [f2fs]
>  __write_node_page+0x339/0x730 [f2fs]
>  f2fs_sync_node_pages+0x5a6/0x780 [f2fs]
>  block_operations+0x257/0x340 [f2fs]
>  f2fs_write_checkpoint+0x102/0x1050 [f2fs]
>  f2fs_gc+0x27c/0x630 [f2fs]
>  ? folio_mark_dirty+0x36/0x70
>  f2fs_balance_fs+0x16f/0x180 [f2fs]
> 
> This patch adds checking whether free sections are enough before checkpoint
> during gc.
> 
> Signed-off-by: Yonggil Song <yonggil.song@...sung.com>
> ---
>  fs/f2fs/gc.c      |  7 ++++++-
>  fs/f2fs/segment.h | 26 +++++++++++++++++++++-----
>  2 files changed, 27 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index 4546e01b2ee0..b22f49a6f128 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -1773,6 +1773,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>  		.iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
>  	};
>  	unsigned int skipped_round = 0, round = 0;
> +	unsigned int nr_needed_secs = 0, node_blocks = 0, dent_blocks = 0;
>  
>  	trace_f2fs_gc_begin(sbi->sb, gc_type, gc_control->no_bg_gc,
>  				gc_control->nr_free_secs,
> @@ -1858,8 +1859,12 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>  		}
>  	}
>  
> +	/* need more three extra sections for writer's data/node/dentry */
> +	nr_needed_secs = get_min_need_secs(sbi, &node_blocks, &dent_blocks) + 3;

	get_min_need_secs(&lower, &upper)
	{
		...

		*lower = node_secs + dent_secs;
		*upper = *lower + (node_blocks ? 1 : 0) + (dent_blocks ? 1 : 0);
	}

> +	nr_needed_secs += ((node_blocks ? 1 : 0) + (dent_blocks ? 1 : 0));
> +
>  	/* Write checkpoint to reclaim prefree segments */
> -	if (free_sections(sbi) < NR_CURSEG_PERSIST_TYPE &&
> +	if (free_sections(sbi) <= nr_needed_secs &&

#define NR_GC_CHECKPOINT_SECS	(3)	/* data/node/dentry sections */

	if (free_sections(sbi) <= upper + NR_GC_CHECKPOINT_SECS &&

>  				prefree_segments(sbi)) {
>  		ret = f2fs_write_checkpoint(sbi, &cpc);
>  		if (ret)
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index be8f2d7d007b..ac11c47bfe37 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -605,8 +605,11 @@ static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi,
>  	return true;
>  }
>  
> -static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
> -					int freed, int needed)
> +/*
> + * calculate the minimum number of sections (needed) for dirty node/dentry
> + */
> +static inline unsigned int get_min_need_secs(struct f2fs_sb_info *sbi,
> +		unsigned int *node_blocks, unsigned int *dent_blocks)
>  {
>  	unsigned int total_node_blocks = get_pages(sbi, F2FS_DIRTY_NODES) +
>  					get_pages(sbi, F2FS_DIRTY_DENTS) +
> @@ -614,15 +617,28 @@ static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
>  	unsigned int total_dent_blocks = get_pages(sbi, F2FS_DIRTY_DENTS);
>  	unsigned int node_secs = total_node_blocks / CAP_BLKS_PER_SEC(sbi);
>  	unsigned int dent_secs = total_dent_blocks / CAP_BLKS_PER_SEC(sbi);
> -	unsigned int node_blocks = total_node_blocks % CAP_BLKS_PER_SEC(sbi);
> -	unsigned int dent_blocks = total_dent_blocks % CAP_BLKS_PER_SEC(sbi);
> +
> +	f2fs_bug_on(sbi, (!node_blocks || !dent_blocks));
> +
> +	*node_blocks = total_node_blocks % CAP_BLKS_PER_SEC(sbi);
> +	*dent_blocks = total_dent_blocks % CAP_BLKS_PER_SEC(sbi);
> +
> +	return (node_secs + dent_secs);
> +}
> +
> +static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
> +					int freed, int needed)
> +{
> +	unsigned int node_blocks = 0;
> +	unsigned int dent_blocks = 0;
>  	unsigned int free, need_lower, need_upper;
>  
>  	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
>  		return false;
>  
>  	free = free_sections(sbi) + freed;
> -	need_lower = node_secs + dent_secs + reserved_sections(sbi) + needed;
> +	need_lower = get_min_need_secs(sbi, &node_blocks, &dent_blocks) + needed +
> +				reserved_sections(sbi);
>  	need_upper = need_lower + (node_blocks ? 1 : 0) + (dent_blocks ? 1 : 0);
>  
>  	if (free > need_upper)
> -- 
> 2.34.1

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