locking/csd_lock: Add boot parameter for controlling CSD lock debugging

mainline inclusion
from mainline-v5.13-rc1
commit 8d0968cc
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5319J

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=35feb60474bf4f7fa7840e14fc7fd344996b919d

--------------------------------

Currently CSD lock debugging can be switched on and off via a kernel
config option only. Unfortunately there is at least one problem with
CSD lock handling pending for about 2 years now, which has been seen
in different environments (mostly when running virtualized under KVM
or Xen, at least once on bare metal). Multiple attempts to catch this
issue have finally led to introduction of CSD lock debug code, but
this code is not in use in most distros as it has some impact on
performance.

In order to be able to ship kernels with CONFIG_CSD_LOCK_WAIT_DEBUG
enabled even for production use, add a boot parameter for switching
the debug functionality on. This will reduce any performance impact
of the debug coding to a bare minimum when not being used.
Signed-off-by: NJuergen Gross <jgross@suse.com>
[ Minor edits. ]
Signed-off-by: NIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210301101336.7797-2-jgross@suse.com
(cherry picked from commit 8d0968cc)

conflicts:
kernel/smp.c

Signed-off-by: Chen Zhongjin chenzhongjin@huawei.com
Reviewed-by: NKuohai Xu <xukuohai@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -800,6 +800,12 @@
 	cs89x0_media=	[HW,NET]
 			Format: { rj45 | aui | bnc }
 
+	csdlock_debug=	[KNL] Enable debug add-ons of cross-CPU function call
+			handling. When switched on, additional debug data is
+			printed to the console in case a hanging CPU is
+			detected, and that CPU is pinged again in order to try
+			to resolve the hang situation.
+
 	dasd=		[HW,NET]
 			See header of drivers/s390/block/dasd_devmap.c.
 

kernel/smp.c

@@ -24,6 +24,7 @@
 #include <linux/sched/clock.h>
 #include <linux/nmi.h>
 #include <linux/sched/debug.h>
+#include <linux/jump_label.h>
 
 #include "smpboot.h"
 #include "sched/smp.h"
@@ -102,6 +103,20 @@ void __init call_function_init(void)
 
 #ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
 
+static DEFINE_STATIC_KEY_FALSE(csdlock_debug_enabled);
+
+static int __init csdlock_debug(char *str)
+{
+	unsigned int val = 0;
+
+	get_option(&str, &val);
+	if (val)
+		static_branch_enable(&csdlock_debug_enabled);
+
+	return 0;
+}
+early_param("csdlock_debug", csdlock_debug);
+
 static DEFINE_PER_CPU(call_single_data_t *, cur_csd);
 static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);
 static DEFINE_PER_CPU(void *, cur_csd_info);
@@ -110,7 +125,7 @@ static DEFINE_PER_CPU(void *, cur_csd_info);
 static atomic_t csd_bug_count = ATOMIC_INIT(0);
 
 /* Record current CSD work for current CPU, NULL to erase. */
-static void csd_lock_record(struct __call_single_data *csd)
+static void __csd_lock_record(struct __call_single_data *csd)
 {
 	if (!csd) {
 		smp_mb(); /* NULL cur_csd after unlock. */
@@ -125,6 +140,12 @@ static void csd_lock_record(struct __call_single_data *csd)
 		  /* Or before unlock, as the case may be. */
 }
 
+static __always_inline void csd_lock_record(struct __call_single_data *csd)
+{
+	if (static_branch_unlikely(&csdlock_debug_enabled))
+		__csd_lock_record(csd);
+}
+
 static __always_inline int csd_lock_wait_getcpu(struct __call_single_data *csd)
 {
 	unsigned int csd_type;
@@ -204,7 +225,7 @@ static __always_inline bool csd_lock_wait_toolong(struct __call_single_data *csd
  * previous function call. For multi-cpu calls its even more interesting
  * as we'll have to ensure no other cpu is observing our csd.
  */
-static __always_inline void csd_lock_wait(struct __call_single_data *csd)
+static void __csd_lock_wait(struct __call_single_data *csd)
 {
 	int bug_id = 0;
 	u64 ts0, ts1;
@@ -218,6 +239,15 @@ static __always_inline void csd_lock_wait(struct __call_single_data *csd)
 	smp_acquire__after_ctrl_dep();
 }
 
+static __always_inline void csd_lock_wait(struct __call_single_data *csd)
+{
+	if (static_branch_unlikely(&csdlock_debug_enabled)) {
+		__csd_lock_wait(csd);
+		return;
+	}
+
+	smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
+}
 #else
 static void csd_lock_record(struct __call_single_data *csd)
 {