[PATCH v3 07/23] ata: libata-scsi: Fix delayed scsi_rescan_device() execution

Damien Le Moal
2023-09-15T08:24:07Z

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>
---
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 0cf0caf77907..0479493e54bd 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -5172,11 +5172,27 @@ 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 ac2d332b4963..6297f8c16a13 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -4760,7 +4760,7 @@ 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);
@@ -4769,37 +4769,34 @@ 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