Re: [PATCH v2] driver core: Fix concurrent problem of deferred_probe_extend_timeout()

["wangwensheng (C)" <wangwensheng4@huawei.com>]

在 2025/8/14 22:19, Greg KH 写道:
> On Thu, Aug 14, 2025 at 08:29:49PM +0800, Wang Wensheng wrote:
>> The deferred_probe_timeout_work may be canceled forever unexpected when
>> deferred_probe_extend_timeout() executes concurrently. Start with
>> deferred_probe_timeout_work pending, and the problem would
>> occur after the following sequence.
>>
>>           CPU0                                 CPU1
>> deferred_probe_extend_timeout
>>    -> cancel_delayed_work => true
>>                                       deferred_probe_extend_timeout
>>                                         -> cancel_delayed_wrok
>>                                           -> __cancel_work
>>                                             -> try_grab_pending
>>    -> schedule_delayed_work
>>     -> queue_delayed_work_on
>> since pending bit is grabbed,
>> just return without doing anything
>>                                          -> set_work_pool_and_clear_pending
>>                                       this __cancel_work return false and
>>                                       the work would never be queued again
>>
>> The root cause is that the PENDING_BIT of the work_struct would be set
>> temporaily in __cancel_work and this bit could prevent the work_struct
>> to be queued in another CPU.
>>
>> Use deferred_probe_mutex to protect the cancel and queue operations for
>> the deferred_probe_timeout_work to fix this problem.
>>
>> Fixes: 2b28a1a84a0e ("driver core: Extend deferred probe timeout on driver registration")
>> Cc: <stable@vger.kernel.org>
>> Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
>> ---
>>   drivers/base/dd.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index 13ab98e033ea..00419d2ee910 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -323,6 +323,7 @@ static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_
>>   
>>   void deferred_probe_extend_timeout(void)
>>   {
>> +	guard(mutex)(&deferred_probe_mutex);
> 
> But if you grab the lock here, in the probe timeout function, the lock
> will be grabbed again, causing a deadlock, right?  If not, why not?

It's not a sync version of cancel_work, so the execuation of the work 
function doesn't block us here, nor does the schedule_delayed_work does.

Indead, deferred_probe_mutex is used to protect the 
deferred_probe_*_list, it looks better to use a new lock here. Right?

> 
> Have you run this patch with lockdep enabled?
> 
> This feels broken to me, what am I missing?
> 
> thanks,
> 
> greg k-h
>