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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
References: <20210427082106.2755-1-frank.li@vivo.com>
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 <8d2e3a63-72f9-bcb2-24e5-dddd84136001@kernel.org>
 <YQR60QUh0Pim8vSf@google.com>
From:   Chao Yu <chao@kernel.org>
Message-ID: <355ac2ff-f1f1-b9ea-bd8c-139cb24a03fb@kernel.org>
Date:   Sun, 1 Aug 2021 17:59:21 +0800
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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?

 From ffb50d9a8220be7d9e159b8555533adcf11957a8 Mon Sep 17 00:00:00 2001
From: Chao Yu <chao@kernel.org>
Date: Mon, 19 Jul 2021 16:37:44 +0800
Subject: [PATCH v2] 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 | 12 +++++++++---
  fs/f2fs/node.c       |  9 ++++++++-
  2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 6c208108d69c..f3f66871ae42 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_stop_checkpoint(sbi, false);
  		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/node.c b/fs/f2fs/node.c
index 5840b82ce311..7162836d71c1 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -141,13 +141,20 @@ static struct page *get_next_nat_page(struct f2fs_sb_info *sbi, nid_t nid)
  	void *src_addr;
  	void *dst_addr;
  	struct f2fs_nm_info *nm_i = NM_I(sbi);
+	bool retried = false;

  	dst_off = next_nat_addr(sbi, current_nat_addr(sbi, nid));

+retry:
  	/* get current nat block page with lock */
  	src_page = get_current_nat_page(sbi, nid);
-	if (IS_ERR(src_page))
+	if (IS_ERR(src_page)) {
+		if (PTR_ERR(src_page) == -ENOMEM && !retried) {
+			retried = true;
+			goto retry;
+		}
  		return src_page;
+	}
  	dst_page = f2fs_grab_meta_page(sbi, dst_off);
  	f2fs_bug_on(sbi, PageDirty(src_page));

-- 
2.22.1