[PATCH v6 07/23] ata: libata-scsi: Fix delayed scsi_rescan_device() execution

[Damien Le Moal <dlemoal@kernel.org>]

Commit 6aa0365a3c85 ("ata: libata-scsi: Avoid deadlock on rescan after
device resume") modified ata_scsi_dev_rescan() to check the scsi device
"is_suspended" power field to ensure that the scsi device associated
with an ATA device is fully resumed when scsi_rescan_device() is
executed. However, this fix is problematic as:
1) It relies on a PM internal field that should not be used without PM
   device locking protection.
2) The check for is_suspended and the call to scsi_rescan_device() are
   not atomic and a suspend PM event may be triggered between them,
   casuing scsi_rescan_device() to be called on a suspended device and
   in that function blocking while holding the scsi device lock. This
   would deadlock a following resume operation.
These problems can trigger PM deadlocks on resume, especially with
resume operations triggered quickly after or during suspend operations.
E.g., a simple bash script like:

for (( i=0; i<10; i++ )); do
	echo "+2 > /sys/class/rtc/rtc0/wakealarm
	echo mem > /sys/power/state
done

that triggers a resume 2 seconds after starting suspending a system can
quickly lead to a PM deadlock preventing the system from correctly
resuming.

Fix this by replacing the check on is_suspended with a check on the
return value given by scsi_rescan_device() as that function will fail if
called against a suspended device. Also make sure rescan tasks already
scheduled are first cancelled before suspending an ata port.

Fixes: 6aa0365a3c85 ("ata: libata-scsi: Avoid deadlock on rescan after device resume")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
---
 drivers/ata/libata-core.c | 16 ++++++++++++++++
 drivers/ata/libata-scsi.c | 33 +++++++++++++++------------------
 2 files changed, 31 insertions(+), 18 deletions(-)

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index a0bc01606b30..092372334e92 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -5168,11 +5168,27 @@ static const unsigned int ata_port_suspend_ehi = ATA_EHI_QUIET
 
 static void ata_port_suspend(struct ata_port *ap, pm_message_t mesg)
 {
+	/*
+	 * We are about to suspend the port, so we do not care about
+	 * scsi_rescan_device() calls scheduled by previous resume operations.
+	 * The next resume will schedule the rescan again. So cancel any rescan
+	 * that is not done yet.
+	 */
+	cancel_delayed_work_sync(&ap->scsi_rescan_task);
+
 	ata_port_request_pm(ap, mesg, 0, ata_port_suspend_ehi, false);
 }
 
 static void ata_port_suspend_async(struct ata_port *ap, pm_message_t mesg)
 {
+	/*
+	 * We are about to suspend the port, so we do not care about
+	 * scsi_rescan_device() calls scheduled by previous resume operations.
+	 * The next resume will schedule the rescan again. So cancel any rescan
+	 * that is not done yet.
+	 */
+	cancel_delayed_work_sync(&ap->scsi_rescan_task);
+
 	ata_port_request_pm(ap, mesg, 0, ata_port_suspend_ehi, true);
 }
 
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index a69d63e7b919..576bb51cb480 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -4756,7 +4756,7 @@ void ata_scsi_dev_rescan(struct work_struct *work)
 	struct ata_link *link;
 	struct ata_device *dev;
 	unsigned long flags;
-	bool delay_rescan = false;
+	int ret = 0;
 
 	mutex_lock(&ap->scsi_scan_mutex);
 	spin_lock_irqsave(ap->lock, flags);
@@ -4765,37 +4765,34 @@ void ata_scsi_dev_rescan(struct work_struct *work)
 		ata_for_each_dev(dev, link, ENABLED) {
 			struct scsi_device *sdev = dev->sdev;
 
+			/*
+			 * If the port was suspended before this was scheduled,
+			 * bail out.
+			 */
+			if (ap->pflags & ATA_PFLAG_SUSPENDED)
+				goto unlock;
+
 			if (!sdev)
 				continue;
 			if (scsi_device_get(sdev))
 				continue;
 
-			/*
-			 * If the rescan work was scheduled because of a resume
-			 * event, the port is already fully resumed, but the
-			 * SCSI device may not yet be fully resumed. In such
-			 * case, executing scsi_rescan_device() may cause a
-			 * deadlock with the PM code on device_lock(). Prevent
-			 * this by giving up and retrying rescan after a short
-			 * delay.
-			 */
-			delay_rescan = sdev->sdev_gendev.power.is_suspended;
-			if (delay_rescan) {
-				scsi_device_put(sdev);
-				break;
-			}
-
 			spin_unlock_irqrestore(ap->lock, flags);
-			scsi_rescan_device(sdev);
+			ret = scsi_rescan_device(sdev);
 			scsi_device_put(sdev);
 			spin_lock_irqsave(ap->lock, flags);
+
+			if (ret)
+				goto unlock;
 		}
 	}
 
+unlock:
 	spin_unlock_irqrestore(ap->lock, flags);
 	mutex_unlock(&ap->scsi_scan_mutex);
 
-	if (delay_rescan)
+	/* Reschedule with a delay if scsi_rescan_device() returned an error */
+	if (ret)
 		schedule_delayed_work(&ap->scsi_rescan_task,
 				      msecs_to_jiffies(5));
 }
-- 
2.41.0