[PATCH V3] scsi: core: put LLD module refcnt after SCSI device is released

[Ming Lei <ming.lei@redhat.com>]

SCSI host release is triggered when SCSI device is freed, and we have to
make sure that LLD module won't be unloaded before SCSI host instance is
released because shost->hostt is required in host release handler.

So make sure to put LLD module refcnt after SCSI device is released.

Fix one kernel panic of 'BUG: unable to handle page fault for address'
reported by Changhui and Yi.

Reported-by: Changhui Zhong <czhong@redhat.com>
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 drivers/scsi/scsi.c        |  4 +++-
 drivers/scsi/scsi_sysfs.c  | 12 ++++++++++++
 include/scsi/scsi_device.h |  1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index b241f9e3885c..291ecc33b1fe 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -553,8 +553,10 @@ EXPORT_SYMBOL(scsi_device_get);
  */
 void scsi_device_put(struct scsi_device *sdev)
 {
-	module_put(sdev->host->hostt->module);
+	struct module *mod = sdev->host->hostt->module;
+
 	put_device(&sdev->sdev_gendev);
+	module_put(mod);
 }
 EXPORT_SYMBOL(scsi_device_put);
 
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 86793259e541..9ada26814011 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -449,9 +449,16 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 	struct scsi_vpd *vpd_pg80 = NULL, *vpd_pg83 = NULL;
 	struct scsi_vpd *vpd_pg0 = NULL, *vpd_pg89 = NULL;
 	unsigned long flags;
+	struct module *mod;
+	bool put_mod = false;
 
 	sdev = container_of(work, struct scsi_device, ew.work);
 
+	if (sdev->put_lld_mod_ref) {
+		mod = sdev->host->hostt->module;
+		put_mod = true;
+	}
+
 	scsi_dh_release_device(sdev);
 
 	parent = sdev->sdev_gendev.parent;
@@ -502,11 +509,16 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 
 	if (parent)
 		put_device(parent);
+	if (put_mod)
+		module_put(mod);
 }
 
 static void scsi_device_dev_release(struct device *dev)
 {
 	struct scsi_device *sdp = to_scsi_device(dev);
+
+	sdp->put_lld_mod_ref = try_module_get(sdp->host->hostt->module);
+
 	execute_in_process_context(scsi_device_dev_release_usercontext,
 				   &sdp->ew);
 }
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 430b73bd02ac..54b46d590e2d 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -206,6 +206,7 @@ struct scsi_device {
 	unsigned rpm_autosuspend:1;	/* Enable runtime autosuspend at device
 					 * creation time */
 	unsigned ignore_media_change:1; /* Ignore MEDIA CHANGE on resume */
+	unsigned put_lld_mod_ref:1;	/* Put LLD module ref in release */
 
 	bool offline_already;		/* Device offline message logged */
 
-- 
2.31.1