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

[Jaegeuk Kim]

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@xxxxxxxxxxx>
> > ---
> >   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

> 
> 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)