[Ocfs2-devel] [PATCH] ocfs2: Fix locking for res->tracking and dlm->tracking_list

From: Changwei Ge <gechangwei@live.cn>
To: ocfs2-devel@oss.oracle.com
Subject: [Ocfs2-devel] [PATCH] ocfs2: Fix locking for res->tracking and dlm->tracking_list
Date: Fri, 22 Jun 2018 01:33:04 +0000	[thread overview]
Message-ID: <HK0PR06MB2532BC29E14CAE4D33E3E91FD5750@HK0PR06MB2532.apcprd06.prod.outlook.com> (raw)
In-Reply-To: <5B2C4406.7030500@huawei.com>

On 2018/6/22 8:34, piaojun wrote:
> Hi Ashish,
>
> I think we should get 'res->spinlock' before getting 'dlm->track_lock'
> such as in __dlm_do_purge_lockres(). But your patch reverse the locking
> sequence as we will get 'res->spinlock' in dlm_print_one_lock_resource()
> which may cause 'ABBA' deadlock.

Agree. This patch could introduce dead lock issue.

> thanks,
> Jun
>
> On 2018/6/22 7:57, Ashish Samant wrote:
>> In dlm_init_lockres() and dlm_unregister_domain() we access and modify
>> res->tracking and dlm->tracking_list without holding dlm->track_lock.
>> This can cause list corruptions and can end up in kernel panic.
>>
>> Fix this by locking res->tracking and dlm->tracking_list with
>> dlm->track_lock at all places.
>>
>> Signed-off-by: Ashish Samant <ashish.samant@oracle.com>
>> ---
>>   fs/ocfs2/dlm/dlmdomain.c | 2 ++
>>   fs/ocfs2/dlm/dlmmaster.c | 4 ++--
>>   2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ocfs2/dlm/dlmdomain.c b/fs/ocfs2/dlm/dlmdomain.c
>> index 2acd58b..cfb1edd 100644
>> --- a/fs/ocfs2/dlm/dlmdomain.c
>> +++ b/fs/ocfs2/dlm/dlmdomain.c
>> @@ -723,6 +723,7 @@ void dlm_unregister_domain(struct dlm_ctxt *dlm)
>>   			mlog(0, "%s: more migration to do\n", dlm->name);
>>   		}
>>   
>> +		spin_lock(&dlm->track_lock);
>>   		/* This list should be empty. If not, print remaining lockres */
>>   		if (!list_empty(&dlm->tracking_list)) {
>>   			mlog(ML_ERROR, "Following lockres' are still on the "
>> @@ -730,6 +731,7 @@ void dlm_unregister_domain(struct dlm_ctxt *dlm)
>>   			list_for_each_entry(res, &dlm->tracking_list, tracking)
>>   				dlm_print_one_lock_resource(res);
>>   		}
>> +		spin_unlock(&dlm->track_lock);
As Jun's comment, above fix is not proper. But the issue Ashish points 
to truly exists.
>>   
>>   		dlm_mark_domain_leaving(dlm);
>>   		dlm_leave_domain(dlm);
>> diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
>> index aaca094..826f056 100644
>> --- a/fs/ocfs2/dlm/dlmmaster.c
>> +++ b/fs/ocfs2/dlm/dlmmaster.c
>> @@ -584,9 +584,9 @@ static void dlm_init_lockres(struct dlm_ctxt *dlm,
>>   
>>   	res->last_used = 0;
>>   
>> -	spin_lock(&dlm->spinlock);
>> +	spin_lock(&dlm->track_lock);
>>   	list_add_tail(&res->tracking, &dlm->tracking_list);
>> -	spin_unlock(&dlm->spinlock);
>> +	spin_unlock(&dlm->track_lock);
Yet, this fix makes sense.

Thanks,
Changwei
>>   
>>   	memset(res->lvb, 0, DLM_LVB_LEN);
>>   	memset(res->refmap, 0, sizeof(res->refmap));
>>
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