Re: [PATCH] scsi: ufs: Fix some problems in task management request implementation

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 01/20, Can Guo wrote:
> Current task management request send/compl implementation is broken, the
> problems and fixes are listed as below:
> 
> Problem: TMR completion timeout. ufshcd_tmc_handler() calls
>          blk_mq_tagset_busy_iter(fn == ufshcd_compl_tm()), but since
>          blk_mq_tagset_busy_iter() only iterates over all reserved tags and
>          started requests, so ufshcd_compl_tm() never gets a chance to run.
> Fix:     Call blk_mq_start_request() in __ufshcd_issue_tm_cmd().
> 
> Problem: Race condition in send/compl paths. ufshcd_compl_tm() looks for
>          all 0 bits in the REG_UTP_TASK_REQ_DOOR_BELL and call complete()
>          for each req who has the req->end_io_data set. There can be a race
>          condition btw tmc send/compl, because req->end_io_data is set, in
>          __ufshcd_issue_tm_cmd(), without host lock protection, so it is
>          possible that when ufshcd_compl_tm() checks the req->end_io_data,
>          req->end_io_data is set but the corresponding tag has not been set
>          in the REG_UTP_TASK_REQ_DOOR_BELL. Thus, ufshcd_tmc_handler() may
>          wrongly complete TMRs which have not been sent.
> Fix:     Protect req->end_io_data with host lock. And let ufshcd_compl_tm()
>          only handle those tm cmds which have been completed instead of
>          looking for 0 bits in the REG_UTP_TASK_REQ_DOOR_BELL.
> 
> Problem: In __ufshcd_issue_tm_cmd(), it is not right to use hba->nutrs +
>          req->tag as the Task Tag in one TMR UPIU.
> Fix:     Directly use req->tag as Task Tag.
> 
> Cc: Jaegeuk Kim <jaegeuk@kernel.org>
> Signed-off-by: Can Guo <cang@codeaurora.org>
> 
> ---
> 
> This change is based on Jaegeuk's change - https://git.kernel.org/mkp/scsi/c/eeb1b55b6e25
> 
> ---
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index fb07e3a..44d09509 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -6252,7 +6252,7 @@ static irqreturn_t ufshcd_check_errors(struct ufs_hba *hba)
>  
>  struct ctm_info {
>  	struct ufs_hba	*hba;
> -	unsigned long	pending;
> +	unsigned long	completed;
>  	unsigned int	ncpl;
>  };
>  
> @@ -6261,13 +6261,13 @@ static bool ufshcd_compl_tm(struct request *req, void *priv, bool reserved)
>  	struct ctm_info *const ci = priv;
>  	struct completion *c;
>  
> -	WARN_ON_ONCE(reserved);
> -	if (test_bit(req->tag, &ci->pending))
> -		return true;
> -	ci->ncpl++;
> -	c = req->end_io_data;
> -	if (c)
> -		complete(c);
> +	if (test_bit(req->tag, &ci->completed)) {
> +		__clear_bit(req->tag, &hba->outstanding_tasks);

Is the below fixed in -next?

		__clear_bit(req->tag, &ci->hba->outstanding_tasks);

> +		ci->ncpl++;
> +		c = req->end_io_data;
> +		if (c)
> +			complete(c);
> +	}
>  	return true;
>  }
>  
> @@ -6283,11 +6283,19 @@ static irqreturn_t ufshcd_tmc_handler(struct ufs_hba *hba)
>  {
>  	struct request_queue *q = hba->tmf_queue;
>  	struct ctm_info ci = {
> -		.hba	 = hba,
> -		.pending = ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL),
> +		.hba = hba,
> +		.ncpl = 0,
>  	};
> +	u32 tm_doorbell;
> +	unsigned long completed;
> +
> +	tm_doorbell = ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL);
> +	completed = tm_doorbell ^ hba->outstanding_tasks;
>  
> -	blk_mq_tagset_busy_iter(q->tag_set, ufshcd_compl_tm, &ci);
> +	if (completed) {
> +		ci.completed = completed;
> +		blk_mq_tagset_busy_iter(q->tag_set, ufshcd_compl_tm, &ci);
> +	}
>  	return ci.ncpl ? IRQ_HANDLED : IRQ_NONE;
>  }
>  
> @@ -6405,37 +6413,33 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba,
>  	DECLARE_COMPLETION_ONSTACK(wait);
>  	struct request *req;
>  	unsigned long flags;
> -	int free_slot, task_tag, err;
> +	int task_tag, err;
>  
>  	/*
> -	 * Get free slot, sleep if slots are unavailable.
> -	 * Even though we use wait_event() which sleeps indefinitely,
> -	 * the maximum wait time is bounded by %TM_CMD_TIMEOUT.
> +	 * blk_get_request() used here is only to get a free tag.
>  	 */
>  	req = blk_get_request(q, REQ_OP_DRV_OUT, 0);
>  	if (IS_ERR(req))
>  		return PTR_ERR(req);
>  
> -	req->end_io_data = &wait;
> -	free_slot = req->tag;
> -	WARN_ON_ONCE(free_slot < 0 || free_slot >= hba->nutmrs);
>  	ufshcd_hold(hba, false);
> -
>  	spin_lock_irqsave(host->host_lock, flags);
> -	task_tag = hba->nutrs + free_slot;
> +	req->end_io_data = &wait;
> +	blk_mq_start_request(req);
>  
> +	task_tag = req->tag;
>  	treq->req_header.dword_0 |= cpu_to_be32(task_tag);
>  
> -	memcpy(hba->utmrdl_base_addr + free_slot, treq, sizeof(*treq));
> -	ufshcd_vops_setup_task_mgmt(hba, free_slot, tm_function);
> +	memcpy(hba->utmrdl_base_addr + task_tag, treq, sizeof(*treq));
> +	ufshcd_vops_setup_task_mgmt(hba, task_tag, tm_function);
>  
>  	/* send command to the controller */
> -	__set_bit(free_slot, &hba->outstanding_tasks);
> +	__set_bit(task_tag, &hba->outstanding_tasks);
>  
>  	/* Make sure descriptors are ready before ringing the task doorbell */
>  	wmb();
>  
> -	ufshcd_writel(hba, 1 << free_slot, REG_UTP_TASK_REQ_DOOR_BELL);
> +	ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL);
>  	/* Make sure that doorbell is committed immediately */
>  	wmb();
>  
> @@ -6447,32 +6451,33 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba *hba,
>  	err = wait_for_completion_io_timeout(&wait,
>  			msecs_to_jiffies(TM_CMD_TIMEOUT));
>  	if (!err) {
> +		spin_lock_irqsave(hba->host->host_lock, flags);
>  		/*
>  		 * Make sure that ufshcd_compl_tm() does not trigger a
>  		 * use-after-free.
>  		 */
>  		req->end_io_data = NULL;
> +		spin_unlock_irqrestore(hba->host->host_lock, flags);
>  		ufshcd_add_tm_upiu_trace(hba, task_tag, "tm_complete_err");
>  		dev_err(hba->dev, "%s: task management cmd 0x%.2x timed-out\n",
>  				__func__, tm_function);
> -		if (ufshcd_clear_tm_cmd(hba, free_slot))
> -			dev_WARN(hba->dev, "%s: unable clear tm cmd (slot %d) after timeout\n",
> -					__func__, free_slot);
> +		if (ufshcd_clear_tm_cmd(hba, task_tag)) {
> +			dev_WARN(hba->dev, "%s: unable to clear tm cmd (slot %d) after timeout\n",
> +					__func__, task_tag);
> +		} else {
> +			__clear_bit(task_tag, &hba->outstanding_tasks);
> +		}
>  		err = -ETIMEDOUT;
>  	} else {
>  		err = 0;
> -		memcpy(treq, hba->utmrdl_base_addr + free_slot, sizeof(*treq));
> +		memcpy(treq, hba->utmrdl_base_addr + task_tag, sizeof(*treq));
>  
>  		ufshcd_add_tm_upiu_trace(hba, task_tag, "tm_complete");
>  	}
>  
> -	spin_lock_irqsave(hba->host->host_lock, flags);
> -	__clear_bit(free_slot, &hba->outstanding_tasks);
> -	spin_unlock_irqrestore(hba->host->host_lock, flags);
> -
> +	ufshcd_release(hba);
>  	blk_put_request(req);
>  
> -	ufshcd_release(hba);
>  	return err;
>  }
>  
> -- 
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