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

[Chao Yu <chao@kernel.org>]

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@samsung.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?

Thanks,

> 
>>
>> Maybe we can add one parameter curseg_no_space for get_need_secs() to get
>> result of has_curseg_enough_space()?
>>
>> static inline void get_need_secs(struct f2fs_sb_info *sbi,
>> 				unsigned int *lower, unsigned int *upper,
>> 				bool *curseg_no_space);
>> {
>> ...
>> 	*lower = node_secs + dent_secs;
>> 	*upper = *lower + (node_blocks ? 1 : 0) + (dent_blocks ? 1 : 0);
>>
>> 	if (curseg_no_space)
>> 		*curseg_no_space =
>> 			!has_curseg_enough_space(sbi, node_blocks, dent_blocks);
>> }
>>
>> Then we can use get_need_secs(, , NULL) in f2fs_gc(),
>> and use get_need_secs(, , &curseg_no_space) in has_not_enough_free_secs()?
>>
>> Thoughts?
>>
>> Thanks,
>>
>>> +
>>> +	/*
>>> +	 * Write checkpoint to reclaim prefree segments.
>>> +	 * We need more three extra sections for writer's data/node/dentry.
>>> +	 */
>>> +	if (free_sections(sbi) <= need_upper + NR_GC_CHECKPOINT_SECS &&
>>>    				prefree_segments(sbi)) {
>>>    		ret = f2fs_write_checkpoint(sbi, &cpc);
>>>    		if (ret)
>>> diff --git a/fs/f2fs/gc.h b/fs/f2fs/gc.h
>>> index 19b956c2d697..e81d22bf3772 100644
>>> --- a/fs/f2fs/gc.h
>>> +++ b/fs/f2fs/gc.h
>>> @@ -30,6 +30,8 @@
>>>    /* Search max. number of dirty segments to select a victim segment */
>>>    #define DEF_MAX_VICTIM_SEARCH 4096 /* covers 8GB */
>>> +#define NR_GC_CHECKPOINT_SECS (3)	/* data/node/dentry sections */
>>> +
>>>    struct f2fs_gc_kthread {
>>>    	struct task_struct *f2fs_gc_task;
>>>    	wait_queue_head_t gc_wait_queue_head;
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index be8f2d7d007b..52a6d1ed4f24 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -605,8 +605,12 @@ 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 needed sections for dirty node/dentry
>>> + * and call has_curseg_enough_space
>>> + */
>>> +static inline bool get_need_secs(struct f2fs_sb_info *sbi,
>>> +				  unsigned int *lower, unsigned int *upper)
>>>    {
>>>    	unsigned int total_node_blocks = get_pages(sbi, F2FS_DIRTY_NODES) +
>>>    					get_pages(sbi, F2FS_DIRTY_DENTS) +
>>> @@ -616,20 +620,33 @@ static inline bool has_not_enough_free_secs(struct f2fs_sb_info *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);
>>> +
>>> +	*lower = node_secs + dent_secs;
>>> +	*upper = *lower + (node_blocks ? 1 : 0) + (dent_blocks ? 1 : 0);
>>> +
>>> +	return !has_curseg_enough_space(sbi, node_blocks, dent_blocks);
>>> +}
>>> +
>>> +static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
>>> +					int freed, int needed)
>>> +{
>>>    	unsigned int free, need_lower, need_upper;
>>> +	bool curseg_enough;
>>>    	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
>>>    		return false;
>>> +	curseg_enough = get_need_secs(sbi, &need_lower, &need_upper);
>>> +
>>>    	free = free_sections(sbi) + freed;
>>> -	need_lower = node_secs + dent_secs + reserved_sections(sbi) + needed;
>>> -	need_upper = need_lower + (node_blocks ? 1 : 0) + (dent_blocks ? 1 : 0);
>>> +	need_lower += (needed + reserved_sections(sbi));
>>> +	need_upper += (needed + reserved_sections(sbi));
>>>    	if (free > need_upper)
>>>    		return false;
>>>    	else if (free <= need_lower)
>>>    		return true;
>>> -	return !has_curseg_enough_space(sbi, node_blocks, dent_blocks);
>>> +	return curseg_enough;
>>>    }
>>>    static inline bool f2fs_is_checkpoint_ready(struct f2fs_sb_info *sbi)


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