Re: [PATCH v2] ufs: core: fix ufshcd_abort_all racing issue

[Bart Van Assche <bvanassche@acm.org>]

On 6/25/24 8:56 PM, Peter Wang (王信友) wrote:
> Sorry I have not explain root-cause clearly.
> I will add more clear root-cause analyze next version.
> 
> And it is not an invalid pointer is passed to blk_mq_unique_tag(),
> I means blk_mq_unique_tag function try access null pointer.
> It is differnt and cause misunderstanding.
> 
> The null pinter blk_mq_unique_tag try access is:
> rq->mq_hctx(NULL)->queue_num.
> 
> The racing flow is:
> 
> Thread A
> ufshcd_err_handler					step 1
> 	ufshcd_cmd_inflight(true)			step 3
> 	ufshcd_mcq_req_to_hwq
> 		blk_mq_unique_tag
> 			rq->mq_hctx->queue_num		step 5
> 
> Thread B				
> ufs_mtk_mcq_intr(cq complete ISR)			step 2
> 	scsi_done						
> 		...
> 		__blk_mq_free_request
> 			rq->mq_hctx = NULL;		step 4

How about surrounding the blk_mq_unique_tag() call with
atomic_inc_not_zero(&req->ref) / atomic_dec(&req->ref)?

Thanks,

Bart.