[tip: locking/core] lockdep: Use raw_cpu_*() for per-cpu variables

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     fddf9055a60dfcc97bda5ef03c8fa4108ed555c5
Gitweb:        https://git.kernel.org/tip/fddf9055a60dfcc97bda5ef03c8fa4108ed555c5
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Thu, 20 Aug 2020 09:13:30 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 26 Aug 2020 12:41:53 +02:00

lockdep: Use raw_cpu_*() for per-cpu variables

Sven reported that commit a21ee6055c30 ("lockdep: Change
hardirq{s_enabled,_context} to per-cpu variables") caused trouble on
s390 because their this_cpu_*() primitives disable preemption which
then lands back tracing.

On the one hand, per-cpu ops should use preempt_*able_notrace() and
raw_local_irq_*(), on the other hand, we can trivialy use raw_cpu_*()
ops for this.

Fixes: a21ee6055c30 ("lockdep: Change hardirq{s_enabled,_context} to per-cpu variables")
Reported-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Tested-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200821085348.192346882@xxxxxxxxxxxxx
---
 include/linux/irqflags.h |  6 +++---
 include/linux/lockdep.h  | 18 +++++++++++++-----
 kernel/locking/lockdep.c |  4 ++--
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index bd5c557..d7e50a2 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -53,13 +53,13 @@ DECLARE_PER_CPU(int, hardirq_context);
   extern void trace_hardirqs_off_finish(void);
   extern void trace_hardirqs_on(void);
   extern void trace_hardirqs_off(void);
-# define lockdep_hardirq_context()	(this_cpu_read(hardirq_context))
+# define lockdep_hardirq_context()	(raw_cpu_read(hardirq_context))
 # define lockdep_softirq_context(p)	((p)->softirq_context)
 # define lockdep_hardirqs_enabled()	(this_cpu_read(hardirqs_enabled))
 # define lockdep_softirqs_enabled(p)	((p)->softirqs_enabled)
 # define lockdep_hardirq_enter()			\
 do {							\
-	if (this_cpu_inc_return(hardirq_context) == 1)	\
+	if (__this_cpu_inc_return(hardirq_context) == 1)\
 		current->hardirq_threaded = 0;		\
 } while (0)
 # define lockdep_hardirq_threaded()		\
@@ -68,7 +68,7 @@ do {						\
 } while (0)
 # define lockdep_hardirq_exit()			\
 do {						\
-	this_cpu_dec(hardirq_context);		\
+	__this_cpu_dec(hardirq_context);	\
 } while (0)
 # define lockdep_softirq_enter()		\
 do {						\
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 62a382d..6a584b3 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -535,19 +535,27 @@ do {									\
 DECLARE_PER_CPU(int, hardirqs_enabled);
 DECLARE_PER_CPU(int, hardirq_context);
 
+/*
+ * The below lockdep_assert_*() macros use raw_cpu_read() to access the above
+ * per-cpu variables. This is required because this_cpu_read() will potentially
+ * call into preempt/irq-disable and that obviously isn't right. This is also
+ * correct because when IRQs are enabled, it doesn't matter if we accidentally
+ * read the value from our previous CPU.
+ */
+
 #define lockdep_assert_irqs_enabled()					\
 do {									\
-	WARN_ON_ONCE(debug_locks && !this_cpu_read(hardirqs_enabled));	\
+	WARN_ON_ONCE(debug_locks && !raw_cpu_read(hardirqs_enabled));	\
 } while (0)
 
 #define lockdep_assert_irqs_disabled()					\
 do {									\
-	WARN_ON_ONCE(debug_locks && this_cpu_read(hardirqs_enabled));	\
+	WARN_ON_ONCE(debug_locks && raw_cpu_read(hardirqs_enabled));	\
 } while (0)
 
 #define lockdep_assert_in_irq()						\
 do {									\
-	WARN_ON_ONCE(debug_locks && !this_cpu_read(hardirq_context));	\
+	WARN_ON_ONCE(debug_locks && !raw_cpu_read(hardirq_context));	\
 } while (0)
 
 #define lockdep_assert_preemption_enabled()				\
@@ -555,7 +563,7 @@ do {									\
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&		\
 		     debug_locks			&&		\
 		     (preempt_count() != 0		||		\
-		      !this_cpu_read(hardirqs_enabled)));		\
+		      !raw_cpu_read(hardirqs_enabled)));		\
 } while (0)
 
 #define lockdep_assert_preemption_disabled()				\
@@ -563,7 +571,7 @@ do {									\
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&		\
 		     debug_locks			&&		\
 		     (preempt_count() == 0		&&		\
-		      this_cpu_read(hardirqs_enabled)));		\
+		      raw_cpu_read(hardirqs_enabled)));			\
 } while (0)
 
 #else
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2fad21d..c872e95 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3756,7 +3756,7 @@ void noinstr lockdep_hardirqs_on(unsigned long ip)
 
 skip_checks:
 	/* we'll do an OFF -> ON transition: */
-	this_cpu_write(hardirqs_enabled, 1);
+	__this_cpu_write(hardirqs_enabled, 1);
 	trace->hardirq_enable_ip = ip;
 	trace->hardirq_enable_event = ++trace->irq_events;
 	debug_atomic_inc(hardirqs_on_events);
@@ -3795,7 +3795,7 @@ void noinstr lockdep_hardirqs_off(unsigned long ip)
 		/*
 		 * We have done an ON -> OFF transition:
 		 */
-		this_cpu_write(hardirqs_enabled, 0);
+		__this_cpu_write(hardirqs_enabled, 0);
 		trace->hardirq_disable_ip = ip;
 		trace->hardirq_disable_event = ++trace->irq_events;
 		debug_atomic_inc(hardirqs_off_events);