linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: fix ref of discard command

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Date:   Wed, 14 Jun 2017 22:58:54 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix ref of discard command

On 2017/6/14 22:26, Jaegeuk Kim wrote:
> On 06/12, Chao Yu wrote:
>> Hi Jaegeuk,
>>
>> On 2017/6/12 11:04, Jaegeuk Kim wrote:
>>> This patch resolves kernel panic for xfstests/081, caused by recent f2fs_bug_on
>>>
>>>   f2fs: add f2fs_bug_on in __remove_discard_cmd
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>> ---
>>>  fs/f2fs/segment.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 86a0c1095939..a6d77388a806 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -1025,6 +1025,8 @@ static void __wait_discard_cmd(struct f2fs_sb_info *sbi, bool wait_cond)
>>>  	list_for_each_entry_safe(dc, tmp, wait_list, list) {
>>>  		if (!wait_cond || (dc->state == D_DONE && !dc->ref)) {
>>>  			wait_for_completion_io(&dc->wait);
>>> +			if (dc->state == D_DONE && dc->ref)
>>> +				dc->ref--;
>>
>> Should set dc->ref to 0 to avoid panic once we add other referrers?
> 
> Sorry, could you please explain this in more detail?

Oh, I just assume later we may add another referrer for some reason
which will make dc->ref = 2, so dc->ref-- is not enough to avoid the
bug_on in __remove_discard_cmd. I think reseting dc->ref is more safe
here, how do you think?

Thanks,

> 
> Thanks,
> 
>>
>> Thanks,
>>
>>>  			__remove_discard_cmd(sbi, dc);
>>>  		} else {
>>>  			dc->ref++;
>>>
> 
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