[PATCH] scsi: storvsc: Fix a panic in the hibernation procedure

[Dexuan Cui <decui@microsoft.com>]

During hibernation, the sdevs are suspended automatically in
drivers/scsi/scsi_pm.c before storvsc_suspend(), so after
storvsc_suspend(), there is no disk I/O from the file systems, but there
can still be disk I/O from the kernel space, e.g. disk_check_events() ->
sr_block_check_events() -> cdrom_check_events() can still submit I/O
to the storvsc driver, which causes a paic of NULL pointer dereference,
since storvsc has closed the vmbus channel in storvsc_suspend(): refer
to the below links for more info:
  https://lkml.org/lkml/2020/4/10/47
  https://lkml.org/lkml/2020/4/17/1103

Fix the panic by blocking/unblocking all the I/O queues properly.

Note: this patch depends on another patch "scsi: core: Allow the state
change from SDEV_QUIESCE to SDEV_BLOCK" (refer to the second link above).

Fixes: 56fb10585934 ("scsi: storvsc: Add the support of hibernation")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 drivers/scsi/storvsc_drv.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index fb41636519ee..fd51d2f03778 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1948,6 +1948,11 @@ static int storvsc_suspend(struct hv_device *hv_dev)
 	struct storvsc_device *stor_device = hv_get_drvdata(hv_dev);
 	struct Scsi_Host *host = stor_device->host;
 	struct hv_host_device *host_dev = shost_priv(host);
+	int ret;
+
+	ret = scsi_host_block(host);
+	if (ret)
+		return ret;
 
 	storvsc_wait_to_drain(stor_device);
 
@@ -1968,10 +1973,15 @@ static int storvsc_suspend(struct hv_device *hv_dev)
 
 static int storvsc_resume(struct hv_device *hv_dev)
 {
+	struct storvsc_device *stor_device = hv_get_drvdata(hv_dev);
+	struct Scsi_Host *host = stor_device->host;
 	int ret;
 
 	ret = storvsc_connect_to_vsp(hv_dev, storvsc_ringbuffer_size,
 				     hv_dev_is_fc(hv_dev));
+	if (!ret)
+		ret = scsi_host_unblock(host, SDEV_RUNNING);
+
 	return ret;
 }
 
-- 
2.19.1