[PATCH v2] scsi: libsas: Fix SMP IO deadlock during HA resume

[Xingui Yang]

When the controller resumes, sas_resume_ha() -> sas_drain_work()
processes the DISCE_RESUME work, which restores the ATA ports through
the libata error handler (ata_sas_port_resume() requests ATA_EH_RESET)
and waits for it in sas_ata_flush_pm_eh(). For an expander-attached
ATA device the hard reset in that recovery is an SMP PHY CONTROL
command sent to the expander:

  ata_eh_recover() -> ata_eh_reset() -> sas_ata_hard_reset()
    -> lldd_I_T_nexus_reset() -> sas_phy_reset()
      -> sas_smp_phy_control() -> smp_execute_task_sg()

For a runtime resume ha->dev is still RPM_RESUMING while the callback
runs, so the pm_runtime_get_sync() in smp_execute_task_sg() blocks
waiting for the resume to complete, but the resume is blocked in
sas_drain_work() waiting for that very SMP IO — a deadlock.

Use pm_runtime_get_noresume()/pm_runtime_put_noidle() when
SAS_HA_RESUMING is set: the usage counter stays elevated for the whole
duration of the IO, so the controller cannot autosuspend underneath an
in-flight SMP IO issued by a thread which the drain does not wait on,
while avoiding the wait for the already ongoing resume. The hardware
is already initialized by the LLDD before sas_resume_ha() runs.
SAS_HA_RESUMING is also set during a system sleep resume, where
ha->dev is RPM_ACTIVE and the noresume variants are harmless.

Outside of the resume window, convert the pm_runtime_get_sync() call
to pm_runtime_resume_and_get() and check the result, so that an SMP IO
is not submitted to a host whose runtime resume failed (the return
value was previously ignored).

Only hisi_sas enables runtime PM among libsas LLDDs, so other drivers
(pm8001, isci, aic94xx, mvsas) are unaffected.

Fixes: 0da7ca4c4fd9 ("scsi: libsas: Resume host while sending SMP I/Os")
Signed-off-by: Xingui Yang <yangxingui@xxxxxxxxxx>
---
Changes since v1:

- Use pm_runtime_get_noresume()/put_noidle() during HA resume instead
  of skipping the PM reference entirely, so an in-flight SMP IO always
  keeps autosuspend away.
- Convert pm_runtime_get_sync() to pm_runtime_resume_and_get() and
  check the result (pre-existing issue flagged by sashiko).

 drivers/scsi/libsas/sas_expander.c | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
index 811c9eb4fef1..43cb90188f44 100644
--- a/drivers/scsi/libsas/sas_expander.c
+++ b/drivers/scsi/libsas/sas_expander.c
@@ -61,8 +61,23 @@ static int smp_execute_task_sg(struct domain_device *dev,
 	struct sas_internal *i =
 		to_sas_internal(dev->port->ha->shost->transportt);
 	struct sas_ha_struct *ha = dev->port->ha;
-
-	pm_runtime_get_sync(ha->dev);
+	bool ha_resuming = test_bit(SAS_HA_RESUMING, &ha->state);
+
+	/*
+	 * While the host is resuming, ha->dev may be RPM_RESUMING and
+	 * the resume blocked in sas_drain_work() waiting for this very
+	 * SMP IO, so waiting for the host to resume here would deadlock.
+	 * Use the noresume/noidle variants to still hold a PM reference
+	 * for the duration of the IO, the hardware is already initialized
+	 * by the LLDD before sas_resume_ha() runs.
+	 */
+	if (ha_resuming) {
+		pm_runtime_get_noresume(ha->dev);
+	} else {
+		res = pm_runtime_resume_and_get(ha->dev);
+		if (res)
+			return res;
+	}
 	mutex_lock(&dev->ex_dev.cmd_mutex);
 	for (retry = 0; retry < 3; retry++) {
 		if (test_bit(SAS_DEV_GONE, &dev->state)) {
@@ -135,7 +150,10 @@ static int smp_execute_task_sg(struct domain_device *dev,
 		}
 	}
 	mutex_unlock(&dev->ex_dev.cmd_mutex);
-	pm_runtime_put_sync(ha->dev);
+	if (ha_resuming)
+		pm_runtime_put_noidle(ha->dev);
+	else
+		pm_runtime_put_sync(ha->dev);
 
 	BUG_ON(retry == 3 && task != NULL);
 	sas_free_task(task);
-- 
2.43.0