linux-kernel - Re: [Ocfs2-devel] [PATCH v2] ocfs2: Fix handle refcount leak in two exception handling paths

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Date:   Thu, 9 Sep 2021 19:07:06 +0800
From:   Joseph Qi <joseph.qi@...ux.alibaba.com>
To:     Wengang Wang <wen.gang.wang@...cle.com>
Cc:     Chenyuan Mi <cymi20@...an.edu.cn>,
        akpm <akpm@...ux-foundation.org>, Xin Tan <tanxin.ctf@...il.com>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        "yuanxzhang@...an.edu.cn" <yuanxzhang@...an.edu.cn>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>
Subject: Re: [Ocfs2-devel] [PATCH v2] ocfs2: Fix handle refcount leak in two
 exception handling paths

Hi Wengang,

On 9/9/21 1:12 AM, Wengang Wang wrote:
> Hi,
> 
> Sorry for late involving, but this doesn’t look right to me.
> 
>> On Sep 8, 2021, at 3:51 AM, Joseph Qi <joseph.qi@...ux.alibaba.com> wrote:
>>
>>
>>
>> On 9/8/21 6:20 PM, Chenyuan Mi wrote:
>>> The reference counting issue happens in two exception handling paths
>>> of ocfs2_replay_truncate_records(). When executing these two exception
>>> handling paths, the function forgets to decrease the refcount of handle
>>> increased by ocfs2_start_trans(), causing a refcount leak.
>>>
>>> Fix this issue by using ocfs2_commit_trans() to decrease the refcount
>>> of handle in two handling paths.
>>>
>>> Signed-off-by: Chenyuan Mi <cymi20@...an.edu.cn>
>>> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
>>> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
>>
>> Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
>>> ---
>>> fs/ocfs2/alloc.c | 2 ++
>>> 1 file changed, 2 insertions(+)
>>>
>>> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
>>> index f1cc8258d34a..b05fde7edc3a 100644
>>> --- a/fs/ocfs2/alloc.c
>>> +++ b/fs/ocfs2/alloc.c
>>> @@ -5940,6 +5940,7 @@ static int ocfs2_replay_truncate_records(struct ocfs2_super *osb,
>>> 		status = ocfs2_journal_access_di(handle, INODE_CACHE(tl_inode), tl_bh,
>>> 						 OCFS2_JOURNAL_ACCESS_WRITE);
>>> 		if (status < 0) {
>>> +			ocfs2_commit_trans(osb, handle);
>>> 			mlog_errno(status);
>>> 			goto bail;
>>> 		}
>>> @@ -5964,6 +5965,7 @@ static int ocfs2_replay_truncate_records(struct ocfs2_super *osb,
>>> 						     data_alloc_bh, start_blk,
>>> 						     num_clusters);
>>> 			if (status < 0) {
>>> +				ocfs2_commit_trans(osb, handle);
> 
> As a transaction, stuff expected to be in the same handle should be treated as atomic.
> Here the stuff includes the tl_bh and other metadata block which will be modified in ocfs2_free_clusters().
> Coming here, some of related meta blocks may be in the handle but others are not due to the error happened.
> If you do a commit, partial meta blocks are committed to log. — that breaks the atomic idea, it will cause FS inconsistency.
> So what’s reason you want to commit the meta block changes, which is not all of expected, in this handle to journal log?
> 
> Do you really see a hit on the failure? or just you detected the refcount leak by code review?
> 
> You may want to look at ocfs2_journal_dirty() for the error handling part.
> 

For the first error handling, since we don't call ocfs2_journal_dirty()
yet, so won't be a problem.
For the second error handling, I think we don't have a better way. Look
at other callers of ocfs2_free_clusters(), we simply ignore the error
code.
Anyway, we should commit transaction if starts, otherwise journal will
be abnormal.

Thanks,
Joseph