Commit baffd723 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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



The thinking in commit:

  fddf9055 ("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:

  1196f12a ("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: fddf9055 ("lockdep: Use raw_cpu_*() for per-cpu variables")
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20201005095958.GJ2651@hirez.programming.kicks-ass.net
parent 4d004099

include/linux/lockdep.h

+9 −17
Original line number Diff line number Diff line
@@ -536,29 +536,21 @@ 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()				\
@@ -566,7 +558,7 @@ 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()				\
@@ -574,7 +566,7 @@ 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

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