Re: [PATCH 1/1] scsi: ufs: core: Fix task management completion timeout race

[Adrian Hunter <adrian.hunter@intel.com>]

On 14/10/2021 19:47, Bart Van Assche wrote:
> On 10/13/21 11:02 PM, Adrian Hunter wrote:
>> On 14/10/2021 07:14, Bart Van Assche wrote:
>>> Wouldn't it be better to keep the code that clears req->end_io_data
>>> and to change complete(c) into if(c) complete(c) in
>>> ufshcd_tmc_handler()?
>>
>> If that were needed, it would imply the synchronization was broken
>> i.e. why are we referencing a request that has already been through
>> blk_put_request()?
> 
> The scenario I'm worried about is as follows:
> * __ufshcd_issue_tm_cmd() issues a task management function.
> * No completion is received before TM_CMD_TIMEOUT has expired (100 ms).
> * ufshcd_clear_tm_cmd() fails.
> * The TMF completes, ufshcd_tmc_handler() is called and that function calls complete(req->end_io_data).
> 
> Can this happen?

No because the tag's bit is cleared from outstanding_tasks before blk_put_request() and
access to outstanding_tasks is protected by host_lock in both __ufshcd_issue_tm_cmd()
and ufshcd_clear_tm_cmd().

> 
> I agree that this scenario involves completion of a request that has already been through blk_put_request().
> 
> Thanks,
> 
> Bart.