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Subject: Re: [f2fs-dev] [PATCH] f2fs: reset free segment to prefree status
 when do_checkpoint() fail
To:     Jaegeuk Kim <jaegeuk@kernel.org>
Cc:     Yangtao Li <frank.li@vivo.com>, linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net
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From:   Chao Yu <chao@kernel.org>
Message-ID: <a37e3ec3-365d-6eb6-85e6-1d7610b93784@kernel.org>
Date:   Tue, 3 Aug 2021 10:57:17 +0800
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On 2021/8/3 9:44, Jaegeuk Kim wrote:
> On 08/03, Chao Yu wrote:
>> On 2021/8/3 1:59, Jaegeuk Kim wrote:
>>> On 08/01, Chao Yu wrote:
>>>> On 2021/7/31 6:18, Jaegeuk Kim wrote:
>>>>> On 07/20, Chao Yu wrote:
>>>>>> On 2021/7/20 2:25, Jaegeuk Kim wrote:
>>>>>>> On 07/19, Chao Yu wrote:
>>>>>>>> On 2021/4/27 20:37, Chao Yu wrote:
>>>>>>>>> I think just reverting dirty/free bitmap is not enough if checkpoint fails,
>>>>>>>>> due to we have updated sbi->cur_cp_pack and nat/sit bitmap, next CP tries
>>>>>>>>> to overwrite last valid meta/node/data, then filesystem will be corrupted.
>>>>>>>>>
>>>>>>>>> So I suggest to set cp_error if do_checkpoint() fails until we can handle
>>>>>>>>> all cases, which is not so easy.
>>>>>>>>>
>>>>>>>>> How do you think?
>>>>>>>>
>>>>>>>> Let's add below patch first before you figure out the patch which covers all
>>>>>>>> things.
>>>>>>>>
>>>>>>>>     From 3af957c98e9e04259f8bb93ca0b74ba164f3f27e Mon Sep 17 00:00:00 2001
>>>>>>>> From: Chao Yu <chao@kernel.org>
>>>>>>>> Date: Mon, 19 Jul 2021 16:37:44 +0800
>>>>>>>> Subject: [PATCH] f2fs: fix to stop filesystem update once CP failed
>>>>>>>>
>>>>>>>> During f2fs_write_checkpoint(), once we failed in
>>>>>>>> f2fs_flush_nat_entries() or do_checkpoint(), metadata of filesystem
>>>>>>>> such as prefree bitmap, nat/sit version bitmap won't be recovered,
>>>>>>>> it may cause f2fs image to be inconsistent, let's just set CP error
>>>>>>>> flag to avoid further updates until we figure out a scheme to rollback
>>>>>>>> all metadatas in such condition.
>>>>>>>>
>>>>>>>> Reported-by: Yangtao Li <frank.li@vivo.com>
>>>>>>>> Signed-off-by: Yangtao Li <frank.li@vivo.com>
>>>>>>>> Signed-off-by: Chao Yu <chao@kernel.org>
>>>>>>>> ---
>>>>>>>>      fs/f2fs/checkpoint.c | 10 +++++++---
>>>>>>>>      1 file changed, 7 insertions(+), 3 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>>>>>>> index 6c208108d69c..096c85022f62 100644
>>>>>>>> --- a/fs/f2fs/checkpoint.c
>>>>>>>> +++ b/fs/f2fs/checkpoint.c
>>>>>>>> @@ -1639,8 +1639,10 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>>>>>>>
>>>>>>>>      	/* write cached NAT/SIT entries to NAT/SIT area */
>>>>>>>>      	err = f2fs_flush_nat_entries(sbi, cpc);
>>>>>>>> -	if (err)
>>>>>>>> +	if (err) {
>>>>>>>> +		f2fs_stop_checkpoint(sbi, false);
>>>>>>>
>>>>>>> I think we should abuse this, since we can get any known ENOMEM as well.
>>>>>>
>>>>>> Yup, but one critical issue here is it can break A/B update of NAT area,
>>>>>> so, in order to fix this hole, how about using NOFAIL memory allocation
>>>>>> in f2fs_flush_nat_entries() first until we figure out the finial scheme?
>>>>>
>>>>> NOFAIL is risky, so how about adding a retry logic on ENOMEM with a message
>>>>> and then giving up if we can't get the memory? BTW, what about EIO or other
>>>>> family?
>>>>
>>>> How about this?
>>>
>>> Hmm, it seems we won't get ENOMEM.
>>>
>>> __flush_nat_entry_set
>>>    -> get_next_nat_page
>>>      -> ...
>>>       -> __get_meta_page
>>>         -> repeat on ENOMEM, but stop_checkpoint on EIO
>>
>> Correct, I missed to check __get_meta_page() and f2fs_get_meta_page_retry().
>>
>>>
>>> If we have an error here, we should have stopped checkpoint. Have you seen other
>>> issue?
>>
>> Still we should fix the case from below path?
>>
>> - f2fs_write_checkpoint
>>   - do_checkpoint
>>    - f2fs_flush_device_cache failed
> 
> What about adding a retry logic to deal with EIO in __submit_flush_wait()?
> We probably need to retry submitting FLUSH commands, and then give up
> with f2fs_stop_checkpoint(). And, then how about adding f2fs_bug_on() if
> f2fs_flush_nat_entries() returns error without f2fs_cp_error()?

Agreed, how about this?

 From 357da99968f6a31375ea47423b691400c5f66547 Mon Sep 17 00:00:00 2001
From: Chao Yu <chao@kernel.org>
Date: Mon, 19 Jul 2021 16:37:44 +0800
Subject: [PATCH v3] f2fs: fix to stop filesystem update once CP failed

During f2fs_write_checkpoint(), once we failed in
f2fs_flush_nat_entries() or do_checkpoint(), metadata of filesystem
such as prefree bitmap, nat/sit version bitmap won't be recovered,
it may cause f2fs image to be inconsistent, let's just set CP error
flag to avoid further updates until we figure out a scheme to rollback
all metadatas in such condition.

Reported-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Chao Yu <chao@kernel.org>
---
v3:
- add f2fs_bug_on in error path of f2fs_flush_nat_entries()
- add retry logic in f2fs_flush_device_cache()
  fs/f2fs/checkpoint.c | 12 +++++++++---
  fs/f2fs/f2fs.h       |  1 +
  fs/f2fs/segment.c    |  8 +++++++-
  3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 6c208108d69c..1d5a2a867282 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1639,8 +1639,11 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)

  	/* write cached NAT/SIT entries to NAT/SIT area */
  	err = f2fs_flush_nat_entries(sbi, cpc);
-	if (err)
+	if (err) {
+		f2fs_err(sbi, "f2fs_flush_nat_entries failed err:%d, stop checkpoint", err);
+		f2fs_bug_on(sbi, !f2fs_cp_error(sbi));
  		goto stop;
+	}

  	f2fs_flush_sit_entries(sbi, cpc);

@@ -1648,10 +1651,13 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
  	f2fs_save_inmem_curseg(sbi);

  	err = do_checkpoint(sbi, cpc);
-	if (err)
+	if (err) {
+		f2fs_err(sbi, "do_checkpoint failed err:%d, stop checkpoint", err);
+		f2fs_stop_checkpoint(sbi, false);
  		f2fs_release_discard_addrs(sbi);
-	else
+	} else {
  		f2fs_clear_prefree_segments(sbi, cpc);
+	}

  	f2fs_restore_inmem_curseg(sbi);
  stop:
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 1feef4cb78b6..97eae0e066ee 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -548,6 +548,7 @@ enum {
  };

  #define DEFAULT_RETRY_IO_COUNT	8	/* maximum retry read IO count */
+#define DEFAULT_RETRY_FLUSH_COUNT	3	/* maximum retry flush count */

  /* congestion wait timeout value, default: 20ms */
  #define	DEFAULT_IO_TIMEOUT	(msecs_to_jiffies(20))
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 80f26158e304..37c7a05659fe 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -776,9 +776,15 @@ int f2fs_flush_device_cache(struct f2fs_sb_info *sbi)
  		return 0;

  	for (i = 1; i < sbi->s_ndevs; i++) {
+		int count = DEFAULT_RETRY_FLUSH_COUNT;
+
  		if (!f2fs_test_bit(i, (char *)&sbi->dirty_device))
  			continue;
-		ret = __submit_flush_wait(sbi, FDEV(i).bdev);
+
+		do {
+			ret = __submit_flush_wait(sbi, FDEV(i).bdev);
+		} while (ret && --count);
+
  		if (ret)
  			break;

-- 
2.22.1