From: Ming Lei <ming.lei@redhat.com>
Date: Fri, 12 Jul 2019 10:08:19 +0800
Subject: scsi: core: Fix race on creating sense cache
Git-commit: f9b0530fa02e0c73f31a49ef743e8f44eb8e32cc
Patch-mainline: v5.3-rc1
References: git-fixes

When scsi_init_sense_cache(host) is called concurrently from different
hosts, each code path may find that no cache has been created and
allocate a new one. The lack of locking can lead to potentially
overriding a cache allocated by a different host.

Fix the issue by moving 'mutex_lock(&scsi_sense_cache_mutex)' before
scsi_select_sense_cache().

Fixes: 0a6ac4ee7c21 ("scsi: respect unchecked_isa_dma for blk-mq")
Cc: Stable <stable@vger.kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Lee Duncan <lduncan@suse.com>
---
 drivers/scsi/scsi_lib.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index ae1c989ef08e..420e2354b36b 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -84,11 +84,11 @@ int scsi_init_sense_cache(struct Scsi_Host *shost)
 	struct kmem_cache *cache;
 	int ret = 0;
 
+	mutex_lock(&scsi_sense_cache_mutex);
 	cache = scsi_select_sense_cache(shost->unchecked_isa_dma);
 	if (cache)
-		return 0;
+		goto exit;
 
-	mutex_lock(&scsi_sense_cache_mutex);
 	if (shost->unchecked_isa_dma) {
 		scsi_sense_isadma_cache =
 			kmem_cache_create("scsi_sense_cache(DMA)",
@@ -104,7 +104,7 @@ int scsi_init_sense_cache(struct Scsi_Host *shost)
 		if (!scsi_sense_cache)
 			ret = -ENOMEM;
 	}
-
+ exit:
 	mutex_unlock(&scsi_sense_cache_mutex);
 	return ret;
 }