linux-kernel - Re: [PATCH v2] f2fs: Fix system crash due to lack of free space in LFS

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Date:   Wed, 5 Apr 2023 08:35:25 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     yonggil.song@...sung.com,
        "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 v2] f2fs: Fix system crash due to lack of free space in
 LFS

On 2023/4/5 5:26, Jaegeuk Kim wrote:
> On 04/04, Chao Yu wrote:
>> On 2023/4/4 1:01, Jaegeuk Kim wrote:
>>> On 04/01, Chao Yu wrote:
>>>> On 2023/3/21 8:12, 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      | 10 ++++++++--
>>>>>     fs/f2fs/gc.h      |  2 ++
>>>>>     fs/f2fs/segment.h | 27 ++++++++++++++++++++++-----
>>>>>     3 files changed, 32 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>>> index 4546e01b2ee0..dd563866d3c9 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 need_lower = 0, need_upper = 0;
>>>>>     	trace_f2fs_gc_begin(sbi->sb, gc_type, gc_control->no_bg_gc,
>>>>>     				gc_control->nr_free_secs,
>>>>> @@ -1858,8 +1859,13 @@ int f2fs_gc(struct f2fs_sb_info *sbi, struct f2fs_gc_control *gc_control)
>>>>>     		}
>>>>>     	}
>>>>> -	/* Write checkpoint to reclaim prefree segments */
>>>>> -	if (free_sections(sbi) < NR_CURSEG_PERSIST_TYPE &&
>>>>> +	ret = get_need_secs(sbi, &need_lower, &need_upper);
>>>>
>>>> Can we avoid calling has_curseg_enough_space() for this case?
>>>
>>> Why? :P
>>
>> We won't check the return value of get_need_secs(), so it's not needed to call
>> has_curseg_enough_space() in get_need_secs() in this path, right?
> 
> I see. Thanks. I think we can do like this:
> 
> Signed-off-by: Yonggil Song <yonggil.song@...sung.com>
> [Jaegeuk Kim: code clean-up]
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>

Better, thanks! :)

Reviewed-by: Chao Yu <chao@...nel.org>

Thanks,