Re: [PATCH v2] f2fs: get victim segment again after new cp

[Jaegeuk Kim <jaegeuk@kernel.org>]

Hi Yunlei,

On Fri, Jul 22, 2016 at 07:08:31PM +0800, Yunlei He wrote:
> Previous selected segment may become free after write_checkpoint,
> if we do garbage collect on this segment, and then new_curseg happen
> to reuse it, it may cause f2fs_bug_on as below.
> 
> 	panic+0x154/0x29c
> 	do_garbage_collect+0x15c/0xaf4
> 	f2fs_gc+0x2dc/0x444
> 	f2fs_balance_fs.part.22+0xcc/0x14c
> 	f2fs_balance_fs+0x28/0x34
> 	f2fs_map_blocks+0x5ec/0x790
> 	f2fs_preallocate_blocks+0xe0/0x100
> 	f2fs_file_write_iter+0x64/0x11c
> 	new_sync_write+0xac/0x11c
> 	vfs_write+0x144/0x1e4
> 	SyS_write+0x60/0xc0
> 
> Here, maybe we check sit and ssa type during reset_curseg. So, we check
> segment is stale or not, and select a new victim to avoid this.
> 
> Signed-off-by: Yunlei He <heyunlei@huawei.com>
> ---
>  fs/f2fs/gc.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index de6c41c..ec17096 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -908,10 +908,14 @@ gc_more:
>  		 * enough free sections, we should flush dent/node blocks and do
>  		 * garbage collections.
>  		 */
> -		if (__get_victim(sbi, &segno, gc_type) || prefree_segments(sbi))
> +		if (__get_victim(sbi, &segno, gc_type) || prefree_segments(sbi)) {
>  			write_checkpoint(sbi, &cpc);
> -		else if (has_not_enough_free_secs(sbi, 0))

If segno is NULL_SEGNO, we get a panic when checking the below conditions.
Anyway, I don't think we need this condition at all.
Let me remove them and just set NULL_SEGNO only after checkpoint.
Please check the dev-test repo.

Thanks,

> +			if(!get_valid_blocks(sbi, segno, sbi->segs_per_sec)
> +					|| IS_CURSEC(sbi, segno / sbi->segs_per_sec))
> +				segno = NULL_SEGNO;
> +		} else if (has_not_enough_free_secs(sbi, 0)) {
>  			write_checkpoint(sbi, &cpc);
> +		}
>  	}
>  
>  	if (segno == NULL_SEGNO && !__get_victim(sbi, &segno, gc_type))
> -- 
> 1.9.1

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