scsi: ufs: add reference counting for scsi block requests

Currently we call the scsi_block_requests()/scsi_unblock_requests()
whenever we want to block/unblock scsi requests but as there is no
reference counting, nesting of these calls could leave us in undesired
state sometime. Consider following call flow sequence:
1. func1() calls scsi_block_requests() but calls func2() before
   calling scsi_unblock_requests()
2. func2() calls scsi_block_requests()
3. func2() calls scsi_unblock_requests()
4. func1() calls scsi_unblock_requests()

As there is no reference counting, we will have scsi requests unblocked
after #3 instead of it to be unblocked only after #4. Though we may not
have failures seen with this, we might run into some failures in future.
Better solution would be to fix this by adding reference counting.

Change-Id: I1eaa39c0716cf41120269cf389ebb322e3006da1
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>

1 files changed, 41 insertions, 11 deletions

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index b2571ac21f39..f7090863971d 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -397,6 +397,36 @@ static inline void ufshcd_disable_irq(struct ufs_hba *hba)
 	}
 }
 
+void ufshcd_scsi_unblock_requests(struct ufs_hba *hba)
+{
+	unsigned long flags;
+	bool unblock = false;
+
+	spin_lock_irqsave(hba->host->host_lock, flags);
+	hba->scsi_block_reqs_cnt--;
+	unblock = !hba->scsi_block_reqs_cnt;
+	spin_unlock_irqrestore(hba->host->host_lock, flags);
+	if (unblock)
+		scsi_unblock_requests(hba->host);
+}
+EXPORT_SYMBOL(ufshcd_scsi_unblock_requests);
+
+static inline void __ufshcd_scsi_block_requests(struct ufs_hba *hba)
+{
+	if (!hba->scsi_block_reqs_cnt++)
+		scsi_block_requests(hba->host);
+}
+
+void ufshcd_scsi_block_requests(struct ufs_hba *hba)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(hba->host->host_lock, flags);
+	__ufshcd_scsi_block_requests(hba);
+	spin_unlock_irqrestore(hba->host->host_lock, flags);
+}
+EXPORT_SYMBOL(ufshcd_scsi_block_requests);
+
 /* replace non-printable or non-ASCII characters with spaces */
 static inline void ufshcd_remove_non_printable(char *val)
 {
@@ -1156,7 +1186,7 @@ static void ufshcd_ungate_work(struct work_struct *work)
 unblock_reqs:
 	if (hba->clk_scaling.is_allowed)
 		ufshcd_resume_clkscaling(hba);
-	scsi_unblock_requests(hba->host);
+	ufshcd_scsi_unblock_requests(hba);
 }
 
 /**
@@ -1197,7 +1227,7 @@ start:
 		 * work and to enable clocks.
 		 */
 	case CLKS_OFF:
-		scsi_block_requests(hba->host);
+		__ufshcd_scsi_block_requests(hba);
 		hba->clk_gating.state = REQ_CLKS_ON;
 		trace_ufshcd_clk_gating(dev_name(hba->dev),
 			hba->clk_gating.state);
@@ -1472,7 +1502,7 @@ start:
 		 * work and exit hibern8.
 		 */
 	case HIBERN8_ENTERED:
-		scsi_block_requests(hba->host);
+		__ufshcd_scsi_block_requests(hba);
 		hba->hibern8_on_idle.state = REQ_HIBERN8_EXIT;
 		trace_ufshcd_hibern8_on_idle(dev_name(hba->dev),
 			hba->hibern8_on_idle.state);
@@ -1635,7 +1665,7 @@ static void ufshcd_hibern8_exit_work(struct work_struct *work)
 		}
 	}
 unblock_reqs:
-	scsi_unblock_requests(hba->host);
+	ufshcd_scsi_unblock_requests(hba);
 }
 
 static ssize_t ufshcd_hibern8_on_idle_delay_show(struct device *dev,
@@ -5115,7 +5145,7 @@ static void ufshcd_exception_event_handler(struct work_struct *work)
 	hba = container_of(work, struct ufs_hba, eeh_work);
 
 	pm_runtime_get_sync(hba->dev);
-	scsi_block_requests(hba->host);
+	ufshcd_scsi_block_requests(hba);
 	err = ufshcd_get_ee_status(hba, &status);
 	if (err) {
 		dev_err(hba->dev, "%s: failed to get exception status %d\n",
@@ -5129,7 +5159,7 @@ static void ufshcd_exception_event_handler(struct work_struct *work)
 		ufshcd_bkops_exception_event_handler(hba);
 
 out:
-	scsi_unblock_requests(hba->host);
+	ufshcd_scsi_unblock_requests(hba);
 	pm_runtime_put_sync(hba->dev);
 	return;
 }
@@ -5392,7 +5422,7 @@ skip_err_handling:
 	ufshcd_clear_eh_in_progress(hba);
 out:
 	spin_unlock_irqrestore(hba->host->host_lock, flags);
-	scsi_unblock_requests(hba->host);
+	ufshcd_scsi_unblock_requests(hba);
 	ufshcd_release_all(hba);
 	pm_runtime_put_sync(hba->dev);
 }
@@ -5498,7 +5528,7 @@ static void ufshcd_check_errors(struct ufs_hba *hba)
 		/* handle fatal errors only when link is functional */
 		if (hba->ufshcd_state == UFSHCD_STATE_OPERATIONAL) {
 			/* block commands from scsi mid-layer */
-			scsi_block_requests(hba->host);
+			__ufshcd_scsi_block_requests(hba);
 
 			hba->ufshcd_state = UFSHCD_STATE_ERROR;
 			schedule_work(&hba->eh_work);
@@ -8232,12 +8262,12 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
 	 * make sure that there are no outstanding requests when
 	 * clock scaling is in progress
 	 */
-	scsi_block_requests(hba->host);
+	ufshcd_scsi_block_requests(hba);
 	down_write(&hba->clk_scaling_lock);
 	if (ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US)) {
 		ret = -EBUSY;
 		up_write(&hba->clk_scaling_lock);
-		scsi_unblock_requests(hba->host);
+		ufshcd_scsi_unblock_requests(hba);
 	}
 
 	return ret;
@@ -8246,7 +8276,7 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
 static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
 {
 	up_write(&hba->clk_scaling_lock);
-	scsi_unblock_requests(hba->host);
+	ufshcd_scsi_unblock_requests(hba);
 }
 
 /**