[PATCH RT 2/2 v3] list_bl: avoid BUG when the list is not locked

[Mikulas Patocka]

list_bl would crash with BUG() if we used it without locking. dm-snapshot 
uses its own locking on realtime kernels (it can't use list_bl because 
list_bl uses raw spinlock and dm-snapshot takes other non-raw spinlocks 
while holding bl_lock).

To avoid this BUG, we must set LIST_BL_LOCKMASK = 0.

This patch is intended only for the realtime kernel patchset, not for the 
upstream kernel.

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>

---
 include/linux/list_bl.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-rt-devel/include/linux/list_bl.h
===================================================================
--- linux-rt-devel.orig/include/linux/list_bl.h	2019-11-13 12:15:50.000000000 +0100
+++ linux-rt-devel/include/linux/list_bl.h	2019-11-13 12:15:50.000000000 +0100
@@ -19,7 +19,7 @@
  * some fast and compact auxiliary data.
  */
 
-#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
+#if (defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)) && !defined(CONFIG_PREEMPT_RT_BASE)
 #define LIST_BL_LOCKMASK	1UL
 #else
 #define LIST_BL_LOCKMASK	0UL