linux-kernel - [PATCH 5.14 01/16] scsi: core: Put LLD module refcnt after SCSI device is released

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Date:   Thu,  4 Nov 2021 15:12:32 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Changhui Zhong <czhong@...hat.com>,
        Yi Zhang <yi.zhang@...hat.com>, Ming Lei <ming.lei@...hat.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: [PATCH 5.14 01/16] scsi: core: Put LLD module refcnt after SCSI device is released

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

commit f2b85040acec9a928b4eb1b57a989324e8e38d3f upstream.

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@...uxfoundation.org>
Reported-by: Changhui Zhong <czhong@...hat.com>
Reported-by: Yi Zhang <yi.zhang@...hat.com>
Tested-by: Yi Zhang <yi.zhang@...hat.com>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/scsi/scsi.c       |    4 +++-
 drivers/scsi/scsi_sysfs.c |    9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

--- 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);
 
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -448,9 +448,12 @@ static void scsi_device_dev_release_user
 	struct scsi_vpd *vpd_pg80 = NULL, *vpd_pg83 = NULL;
 	struct scsi_vpd *vpd_pg0 = NULL, *vpd_pg89 = NULL;
 	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;
@@ -501,11 +504,17 @@ static void scsi_device_dev_release_user
 
 	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);
 }