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Subject[PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled synchronisation with actual irq state
Date
If an interrupt is not masked by local_irq_disable (e.g., a powerpc perf
interrupt), then it can hit in local_irq_enable() after trace_hardirqs_on()
and before raw_local_irq_enable().

If that interrupt handler calls local_irq_save(), it will call
trace_hardirqs_off() but the local_irq_restore() will not call
trace_hardirqs_on() again because raw_irqs_disabled_flags(flags) is true.

This can lead lockdep_assert_irqs_enabled() to trigger false positive
warnings.

Fix this by being careful to only enable and disable trace_hardirqs with
the outer-most irq enable/disable.

Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---

I haven't tested on other architectures but I imagine NMIs in general
might cause a similar problem.

Other architectures might have to be updated for patch 2, but there's
a lot of asm around interrupt/return, so I didn't have a very good
lock. The warnings should be harmless enough and uncover most places
that need updating.

arch/powerpc/include/asm/hw_irq.h | 11 ++++-------
include/linux/irqflags.h | 29 ++++++++++++++++++-----------
2 files changed, 22 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
index 3a0db7b0b46e..35060be09073 100644
--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h
@@ -200,17 +200,14 @@ static inline bool arch_irqs_disabled(void)
#define powerpc_local_irq_pmu_save(flags) \
do { \
raw_local_irq_pmu_save(flags); \
- trace_hardirqs_off(); \
+ if (!raw_irqs_disabled_flags(flags)) \
+ trace_hardirqs_off(); \
} while(0)
#define powerpc_local_irq_pmu_restore(flags) \
do { \
- if (raw_irqs_disabled_flags(flags)) { \
- raw_local_irq_pmu_restore(flags); \
- trace_hardirqs_off(); \
- } else { \
+ if (!raw_irqs_disabled_flags(flags)) \
trace_hardirqs_on(); \
- raw_local_irq_pmu_restore(flags); \
- } \
+ raw_local_irq_pmu_restore(flags); \
} while(0)
#else
#define powerpc_local_irq_pmu_save(flags) \
diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 6384d2813ded..571ee29ecefc 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -163,26 +163,33 @@ do { \
* if !TRACE_IRQFLAGS.
*/
#ifdef CONFIG_TRACE_IRQFLAGS
-#define local_irq_enable() \
- do { trace_hardirqs_on(); raw_local_irq_enable(); } while (0)
-#define local_irq_disable() \
- do { raw_local_irq_disable(); trace_hardirqs_off(); } while (0)
+#define local_irq_enable() \
+ do { \
+ trace_hardirqs_on(); \
+ raw_local_irq_enable(); \
+ } while (0)
+
+#define local_irq_disable() \
+ do { \
+ bool was_disabled = raw_irqs_disabled(); \
+ raw_local_irq_disable(); \
+ if (!was_disabled) \
+ trace_hardirqs_off(); \
+ } while (0)
+
#define local_irq_save(flags) \
do { \
raw_local_irq_save(flags); \
- trace_hardirqs_off(); \
+ if (!raw_irqs_disabled_flags(flags)) \
+ trace_hardirqs_off(); \
} while (0)


#define local_irq_restore(flags) \
do { \
- if (raw_irqs_disabled_flags(flags)) { \
- raw_local_irq_restore(flags); \
- trace_hardirqs_off(); \
- } else { \
+ if (!raw_irqs_disabled_flags(flags)) \
trace_hardirqs_on(); \
- raw_local_irq_restore(flags); \
- } \
+ raw_local_irq_restore(flags); \
} while (0)

#define safe_halt() \
--
2.23.0
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