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

Jaegeuk Kim
2021-01-21T03:03:07Z

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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