[PATCH v2 1/4] scsi: sd: Let sd_shutdown() fail future I/O

[Bart Van Assche <bvanassche@acm.org>]

System shutdown happens as follows (see e.g. the systemd source file
src/shutdown/shutdown.c):
* sync() is called.
* reboot(RB_AUTOBOOT/RB_HALT_SYSTEM/RB_POWER_OFF) is called.
* If the reboot() system call returns, log an error message.

The reboot() system call causes the kernel to call kernel_restart(),
kernel_halt() or kernel_power_off(). Each of these functions calls
device_shutdown(). device_shutdown() calls sd_shutdown(). After
sd_shutdown() has been called the .shutdown() callback of the LLD
will be called. Hence, I/O submitted after sd_shutdown() will hang or
may even cause a kernel crash.

Let sd_shutdown() fail future I/O such that LLD .shutdown() callbacks
can be simplified.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Mike Christie <michael.christie@oracle.com>
Cc: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/sd.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 4bb87043e6db..4017b5412ba4 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3699,12 +3699,13 @@ static int sd_start_stop_device(struct scsi_disk *sdkp, int start)
 static void sd_shutdown(struct device *dev)
 {
 	struct scsi_disk *sdkp = dev_get_drvdata(dev);
+	struct request_queue *q;
 
 	if (!sdkp)
 		return;         /* this can happen */
 
 	if (pm_runtime_suspended(dev))
-		return;
+		goto fail_future_io;
 
 	if (sdkp->WCE && sdkp->media_present) {
 		sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
@@ -3715,6 +3716,14 @@ static void sd_shutdown(struct device *dev)
 		sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
 		sd_start_stop_device(sdkp, 0);
 	}
+
+fail_future_io:
+	q = sdkp->disk->queue;
+	blk_queue_flag_set(QUEUE_FLAG_DYING, q);
+	if (!scsi_host_busy(sdkp->device->host))
+		return;
+	blk_mq_freeze_queue(q);
+	blk_mq_unfreeze_queue(q);
 }
 
 static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)