[Ocfs2-devel] [PATCH 1/1] o2dlm: fix NULL pointer dereference in o2dlm_blocking_ast_wrapper

[Srinivas Eeda]

On 01/13/2014 07:37 AM, Joel Becker wrote:
> On Fri, Jan 10, 2014 at 05:19:13PM -0800, Srinivas Eeda wrote:
>> From: Srinivas Eeda <seeda at srini.(none)>
>>
>> A tiny race between BAST and unlock message causes the NULL dereference.
>>
>> A node sends an unlock request to master and receives a response. Before
>> processing the response it receives a BAST from the master. Since both requests
>> are processed by different threads it creates a race. While the BAST is being
>> processed, lock can get freed by unlock code.
>>
>> This patch makes bast to return immediately if lock is found but unlock is
>> pending. The code should handle this race. We also have to fix master node to
>> skip sending BAST after receiving unlock message.
> Did the master send the BAST after the unlock, or does that race too?
> Does the master know the unlock has succeeded, or does it just think so?
I think it's due to a race but I haven't debugged the master. My guess 
is unlock request sneaked in before the dlm_flush_asts was called. 
However non master node should handle this race as well, so just did 
that part which fixed a bug we were seeing.


>
>> @@ -385,8 +385,13 @@ int dlm_proxy_ast_handler(struct o2net_msg *msg, u32 len, void *data,
>>   		head = &res->granted;
>>   
>>   	list_for_each_entry(lock, head, list) {
>> -		if (lock->ml.cookie == cookie)
>> -			goto do_ast;
>> +		/* if lock is found but unlock is pending ignore the bast */
>> +		if (lock->ml.cookie == cookie) {
>> +			if (lock->unlock_pending)
>> +				break;
>> +			else
>> +				goto do_ast;
>> +		}
> This breaks out for asts as well as basts.  Can't that cause problems
> with the unlock ast expected by the caller?
if unlock_pending is set, then the node is trying to unlock an existing 
lock and shouldn't receive any asts ?
>
> Joel
>
>