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Message-ID: <28512520-d8fe-839f-67ab-45f89f12968d@huawei.com>
Date: Wed, 7 Aug 2019 11:37:22 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Sahitya Tummala <stummala@...eaurora.org>
CC: Jaegeuk Kim <jaegeuk@...nel.org>,
<linux-f2fs-devel@...ts.sourceforge.net>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] f2fs: Fix indefinite loop in f2fs_gc()
Hi Sahitya,
On 2019/8/7 11:24, Sahitya Tummala wrote:
> Hi Chao,
>
> On Wed, Aug 07, 2019 at 10:04:16AM +0800, Chao Yu wrote:
>> Hi Sahitya,
>>
>> On 2019/8/6 19:19, Sahitya Tummala wrote:
>>> Policy - Foreground GC, LFS and greedy GC mode.
>>>
>>> Under this policy, f2fs_gc() loops forever to GC as it doesn't have
>>> enough free segements to proceed and thus it keeps calling gc_more
>>> for the same victim segment. This can happen if the selected victim
>>> segment could not be GC'd due to failed blkaddr validity check i.e.
>>> is_alive() returns false for the blocks set in current validity map.
>>>
>>> Fix this by keeping track of such invalid segments and skip those
>>> segments for selection in get_victim_by_default() to avoid endless
>>> GC loop under such error scenarios.
>>>
>>> Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>
>>> ---
>>> v2: fix as per Chao's suggestion to handle this error case
>>>
>>> fs/f2fs/gc.c | 15 ++++++++++++++-
>>> fs/f2fs/segment.c | 5 +++++
>>> fs/f2fs/segment.h | 3 +++
>>> 3 files changed, 22 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>> index 8974672..321a78a 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -382,6 +382,14 @@ static int get_victim_by_default(struct f2fs_sb_info *sbi,
>>> nsearched++;
>>> }
>>>
>>> + /*
>>> + * skip selecting the invalid segno (that is failed due to block
>>> + * validity check failed during GC) to avoid endless GC loop in
>>> + * such cases.
>>> + */
>>> + if (test_bit(segno, sm->invalid_segmap))
>>> + goto next;
>>> +
>>> secno = GET_SEC_FROM_SEG(sbi, segno);
>>>
>>> if (sec_usage_check(sbi, secno))
>>> @@ -975,6 +983,7 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>>> int off;
>>> int phase = 0;
>>> int submitted = 0;
>>> + struct sit_info *sit_i = SIT_I(sbi);
>>>
>>> start_addr = START_BLOCK(sbi, segno);
>>>
>>> @@ -1008,8 +1017,12 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>>> }
>>>
>>> /* Get an inode by ino with checking validity */
>>> - if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs))
>>> + if (!is_alive(sbi, entry, &dni, start_addr + off, &nofs)) {
>>> + if (!test_and_set_bit(segno, sit_i->invalid_segmap))
>>> + f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
>>> + start_addr + off, segno);
>>
>> Oh, there is some normal cases in is_alive(), such as f2fs_get_node_page() or
>> f2fs_get_node_info() failure due to no memory, we should bypass such cases. I
>
> Oh, yes, I have missed this point.
>
>> guess something like this:
>>
>> if (source_blkaddr != blkaddr) {
>> if (unlikely(check_valid_map(sbi, segno, off))) {
>
> check_valid_map() is validated before is_alive(). So I think this check again
> may not be needed. What do you think?
> race in between is_alive() and update_sit_entry()
There will be a race case:
gc_data_segment f2fs_truncate_data_blocks_range
check_valid_map
f2fs_invalidate_blocks
update_sit_entry
f2fs_test_and_clear_bit(, se->cur_valid_map);
unlock_page(node_page)
is_alive
lock_page(node_page)
blkaddr should be NULL and not equal to source_blkaddr, I think this is a normal
case, right?
Thanks,
>
>> if (!test_and_set_bit(segno, sit_i->invalid_segmap)) {
>> f2fs_err(sbi, "invalid blkaddr %u in seg %u is found\n",
>> start_addr + off, segno);
>> set_sbi_flag(sbi, SBI_NEED_FSCK);
>> }
>> }
>> return false;
>> }
>>
>> I think this will be safe to call check_valid_map(), because there should be no
>> race in between is_alive() and update_sit_entry() from all paths due to node
>> page lock dependence.
>>
>> One more concern is should we use this under CONFIG_F2FS_CHECK_FS? If there is
>> actually such a bug can cause data inconsistency, we'd better find the root
>> cause in debug version.
>>
>
> Yes, I agree with you. I will include this under CONFIG_F2FS_CHECK_FS.
>
> Thanks,
>
>> Thanks,
>>
>>> continue;
>>> + }
>>>
>>> if (phase == 2) {
>>> f2fs_ra_node_page(sbi, dni.ino);
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index a661ac3..d45a1d3 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -4017,6 +4017,10 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
>>> return -ENOMEM;
>>> #endif
>>>
>>> + sit_i->invalid_segmap = f2fs_kvzalloc(sbi, bitmap_size, GFP_KERNEL);
>>> + if (!sit_i->invalid_segmap)
>>> + return -ENOMEM;
>>> +
>>> /* init SIT information */
>>> sit_i->s_ops = &default_salloc_ops;
>>>
>>> @@ -4518,6 +4522,7 @@ static void destroy_sit_info(struct f2fs_sb_info *sbi)
>>> #ifdef CONFIG_F2FS_CHECK_FS
>>> kvfree(sit_i->sit_bitmap_mir);
>>> #endif
>>> + kvfree(sit_i->invalid_segmap);
>>> kvfree(sit_i);
>>> }
>>>
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index b746028..bc5dbe8 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -246,6 +246,9 @@ struct sit_info {
>>> unsigned long long min_mtime; /* min. modification time */
>>> unsigned long long max_mtime; /* max. modification time */
>>>
>>> + /* list of segments to be ignored by GC in case of errors */
>>> + unsigned long *invalid_segmap;
>>> +
>>> unsigned int last_victim[MAX_GC_POLICY]; /* last victim segment # */
>>> };
>>>
>>>
>
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