[PATCH v2] scsi: ufs: core: Prevent MMIO access and drain in-flight commands during shutdown

[Stanley Jhu <stanleyjhu@google.com>]

Commit 19a198b67767 ("scsi: ufs: core: Set SDEV_OFFLINE when UFS is
shut down") replaced scsi_device_quiesce() with
scsi_device_set_state(sdev, SDEV_OFFLINE) in ufshcd_wl_shutdown() to
avoid unbounded blk_mq_freeze_queue() deadlocks when a reboot occurs
early during boot. However, unlike scsi_device_quiesce(), setting
SDEV_OFFLINE is a state write only and does not wait for in-flight or
currently dispatching requests to drain.

As a result, ufshcd_wl_shutdown() immediately sends START STOP UNIT
(PowerDown) and powers off the UFS controller (is_powered = false,
regulators disabled, clocks gated) while regular LUNs may still have
commands outstanding or threads preempted between scsi_queue_rq() and
ufshcd_queuecommand(). Writing to MMIO registers of a power-gated or
clock-gated controller triggers hardware bus errors, system hangs, or
kernel panics.

Close this window without reintroducing the unbounded freeze deadlock:
1. In ufshcd_wl_shutdown(), invoke ufshcd_wait_for_pending_cmds() with a
   bounded 1-second timeout after marking regular LUNs SDEV_OFFLINE so
   in-flight transfer and task management requests drain before the
   device enters powerdown mode and controller clocks/regulators are
   disabled.
2. In ufshcd_queuecommand(), check hba->shutting_down and reject any
   stray non-WLUN / non-PM requests with DID_NO_CONNECT before touching
   MMIO registers, covering threads preempted across the bounded drain
   window.

Fixes: 19a198b67767 ("scsi: ufs: core: Set SDEV_OFFLINE when UFS is shut down")
Cc: stable@vger.kernel.org
Reviewed-by: Peter Wang <peter.wang@mediatek.com>
Signed-off-by: Stanley Jhu <stanleyjhu@google.com>
---
Changes since v1:
- Correct the commit subject in the Fixes: tag and clarify why a bounded
  drain is used instead of restoring scsi_device_quiesce().
- Collect Reviewed-by from Peter Wang (sent off-list due to mail gateway
  headers). No code changes.

 drivers/ufs/core/ufshcd.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 2ba244cf40ac..6d78e34a19b2 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -3105,6 +3105,25 @@ static enum scsi_qc_status ufshcd_queuecommand(struct Scsi_Host *host,
 	int err = 0;
 	struct ufs_hw_queue *hwq = NULL;
 
+	/*
+	 * During host shutdown, fail any incoming regular I/O commands
+	 * immediately. This prevents stray requests that bypassed SCSI queue
+	 * offline checks from writing to MMIO doorbells after the controller
+	 * is power-gated (causing fatal bus errors / panics).
+	 *
+	 * Note: Checking !hba->is_powered is not needed here because:
+	 * 1. During shutdown, hba->shutting_down is set prior to cutting
+	 *    controller power, so shutting_down alone fully covers the
+	 *    unpowered window.
+	 * 2. During module removal, scsi_remove_host() freezes and destroys
+	 *    all request queues before hba->is_powered is set to false in
+	 *    ufshcd_hba_exit().
+	 */
+	if (unlikely(READ_ONCE(hba->shutting_down))) {
+		if (!is_device_wlun(cmd->device) ||
+		    !(scsi_cmd_to_rq(cmd)->rq_flags & RQF_PM)) {
+			set_host_byte(cmd, DID_NO_CONNECT);
+			scsi_done(cmd);
+			return 0;
+		}
+	}
+
 	switch (hba->ufshcd_state) {
 	case UFSHCD_STATE_OPERATIONAL:
 		break;
@@ -10931,6 +10950,14 @@ static void ufshcd_wl_shutdown(struct scsi_device *sdev)
 		scsi_device_set_state(sdev, SDEV_OFFLINE);
 		mutex_unlock(&sdev->state_mutex);
 	}
+
+	/*
+	 * Drain all in-flight transfer and task management requests before
+	 * putting the device into low power and turning off controller power.
+	 */
+	if (ufshcd_wait_for_pending_cmds(hba, USEC_PER_SEC))
+		dev_warn(hba->dev,
+			 "timed out waiting for in-flight commands during shutdown\n");
+
 	__ufshcd_wl_suspend(hba, UFS_SHUTDOWN_PM);
 
 	/*
-- 
2.55.0.1082.g2b9226bbc0-goog