[PATCH AUTOSEL 4.4 1/3] scsi: core: Put LLD module refcnt after SCSI device is released

[Sasha Levin <sashal@kernel.org>]

From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit f2b85040acec9a928b4eb1b57a989324e8e38d3f ]

SCSI host release is triggered when SCSI device is freed. We have to make
sure that the low-level device driver module won't be unloaded before SCSI
host instance is released because shost->hostt is required in the release
handler.

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

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

Link: https://lore.kernel.org/r/20211008050118.1440686-1-ming.lei@redhat.com
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reported-by: Changhui Zhong <czhong@redhat.com>
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/scsi/scsi.c       | 4 +++-
 drivers/scsi/scsi_sysfs.c | 9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index d07fb653f5dc..d59ce94fdf73 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -936,8 +936,10 @@ 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 b89af3841e44..7497917afdec 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -396,9 +396,12 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 	struct device *parent;
 	struct list_head *this, *tmp;
 	unsigned long flags;
+	struct module *mod;
 
 	sdev = container_of(work, struct scsi_device, ew.work);
 
+	mod = sdev->host->hostt->module;
+
 	scsi_dh_release_device(sdev);
 
 	parent = sdev->sdev_gendev.parent;
@@ -430,11 +433,17 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 
 	if (parent)
 		put_device(parent);
+	module_put(mod);
 }
 
 static void scsi_device_dev_release(struct device *dev)
 {
 	struct scsi_device *sdp = to_scsi_device(dev);
+
+	/* Set module pointer as NULL in case of module unloading */
+	if (!try_module_get(sdp->host->hostt->module))
+		sdp->host->hostt->module = NULL;
+
 	execute_in_process_context(scsi_device_dev_release_usercontext,
 				   &sdp->ew);
 }
-- 
2.33.0