linux-kernel - [tip: locking/core] lockdep: Revert "lockdep: Use raw_cpu

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Message-ID: <160208761223.7002.12830126769485268107.tip-bot2@tip-bot2>
Date:   Wed, 07 Oct 2020 16:20:12 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/core] lockdep: Revert "lockdep: Use raw_cpu_*() for
 per-cpu variables"

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

Commit-ID:     820d8a6c966343059ba58b9a82f570f27bf147d6
Gitweb:        https://git.kernel.org/tip/820d8a6c966343059ba58b9a82f570f27bf147d6
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Mon, 05 Oct 2020 09:56:57 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 07 Oct 2020 18:14:17 +02:00

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

The thinking in commit:

  fddf9055a60d ("lockdep: Use raw_cpu_*() for per-cpu variables")

is flawed. While it is true that when we're migratable both CPUs will
have a 0 value, it doesn't hold that when we do get migrated in the
middle of a raw_cpu_op(), the old CPU will still have 0 by the time we
get around to reading it on the new CPU.

Luckily, the reason for that commit (s390 using preempt_disable()
instead of preempt_disable_notrace() in their percpu code), has since
been fixed by commit:

  1196f12a2c96 ("s390: don't trace preemption in percpu macros")

An audit of arch/*/include/asm/percpu*.h shows there are no other
architectures affected by this particular issue.

Fixes: fddf9055a60d ("lockdep: Use raw_cpu_*() for per-cpu variables")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20201005095958.GJ2651@hirez.programming.kicks-ass.net
---
 include/linux/lockdep.h | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 1cc9825..f559487 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -537,19 +537,19 @@ do {									\
 #define lock_map_release(l)			lock_release(l, _THIS_IP_)
 
 #ifdef CONFIG_PROVE_LOCKING
-# define might_lock(lock) 						\
+# define might_lock(lock)						\
 do {									\
 	typecheck(struct lockdep_map *, &(lock)->dep_map);		\
 	lock_acquire(&(lock)->dep_map, 0, 0, 0, 1, NULL, _THIS_IP_);	\
 	lock_release(&(lock)->dep_map, _THIS_IP_);			\
 } while (0)
-# define might_lock_read(lock) 						\
+# define might_lock_read(lock)						\
 do {									\
 	typecheck(struct lockdep_map *, &(lock)->dep_map);		\
 	lock_acquire(&(lock)->dep_map, 0, 0, 1, 1, NULL, _THIS_IP_);	\
 	lock_release(&(lock)->dep_map, _THIS_IP_);			\
 } while (0)
-# define might_lock_nested(lock, subclass) 				\
+# define might_lock_nested(lock, subclass)				\
 do {									\
 	typecheck(struct lockdep_map *, &(lock)->dep_map);		\
 	lock_acquire(&(lock)->dep_map, subclass, 0, 1, 1, NULL,		\
@@ -561,29 +561,21 @@ DECLARE_PER_CPU(int, hardirqs_enabled);
 DECLARE_PER_CPU(int, hardirq_context);
 DECLARE_PER_CPU(unsigned int, lockdep_recursion);
 
-/*
- * 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_enabled	(debug_locks && !raw_cpu_read(lockdep_recursion))
+#define __lockdep_enabled	(debug_locks && !this_cpu_read(lockdep_recursion))
 
 #define lockdep_assert_irqs_enabled()					\
 do {									\
-	WARN_ON_ONCE(__lockdep_enabled && !raw_cpu_read(hardirqs_enabled)); \
+	WARN_ON_ONCE(__lockdep_enabled && !this_cpu_read(hardirqs_enabled)); \
 } while (0)
 
 #define lockdep_assert_irqs_disabled()					\
 do {									\
-	WARN_ON_ONCE(__lockdep_enabled && raw_cpu_read(hardirqs_enabled)); \
+	WARN_ON_ONCE(__lockdep_enabled && this_cpu_read(hardirqs_enabled)); \
 } while (0)
 
 #define lockdep_assert_in_irq()						\
 do {									\
-	WARN_ON_ONCE(__lockdep_enabled && !raw_cpu_read(hardirq_context)); \
+	WARN_ON_ONCE(__lockdep_enabled && !this_cpu_read(hardirq_context)); \
 } while (0)
 
 #define lockdep_assert_preemption_enabled()				\
@@ -591,7 +583,7 @@ do {									\
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&		\
 		     __lockdep_enabled			&&		\
 		     (preempt_count() != 0		||		\
-		      !raw_cpu_read(hardirqs_enabled)));		\
+		      !this_cpu_read(hardirqs_enabled)));		\
 } while (0)
 
 #define lockdep_assert_preemption_disabled()				\
@@ -599,7 +591,7 @@ do {									\
 	WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT)	&&		\
 		     __lockdep_enabled			&&		\
 		     (preempt_count() == 0		&&		\
-		      raw_cpu_read(hardirqs_enabled)));			\
+		      this_cpu_read(hardirqs_enabled)));		\
 } while (0)
 
 #else