Hi Jaegeuk,
On 2016/7/23 2:59, Jaegeuk Kim wrote:
> 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 <[email protected]>
>> ---
>> 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.
I thinks the condition which trigger our f2fs_bug_on is really a corner case,
we'd better not waste the victim we found everytime, especially for these
victims from last background gc's victims.
What about checking segno first?
if(segno != NULL_SEGNO && (!get_valid_blocks(sbi, segno, sbi->segs_per_sec) ||
IS_CURSEC(sbi, GET_SECNO(sbi, segno)))
segno = NULL_SEGNO;
Thanks,
> 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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