From 044d0d6de9f50192f9697583504a382347ee95ca Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Thu, 23 Jul 2020 20:56:14 +1000
Subject: lockdep: Only trace IRQ edges
Problem:
raw_local_irq_save(); // software state on
local_irq_save(); // software state off
...
local_irq_restore(); // software state still off, because we don't enable IRQs
raw_local_irq_restore(); // software state still off, *whoopsie*
existing instances:
- lock_acquire()
raw_local_irq_save()
__lock_acquire()
arch_spin_lock(&graph_lock)
pv_wait() := kvm_wait() (same or worse for Xen/HyperV)
local_irq_save()
- trace_clock_global()
raw_local_irq_save()
arch_spin_lock()
pv_wait() := kvm_wait()
local_irq_save()
- apic_retrigger_irq()
raw_local_irq_save()
apic->send_IPI() := default_send_IPI_single_phys()
local_irq_save()
Possible solutions:
A) make it work by enabling the tracing inside raw_*()
B) make it work by keeping tracing disabled inside raw_*()
C) call it broken and clean it up now
Now, given that the only reason to use the raw_* variant is because you don't
want tracing. Therefore A) seems like a weird option (although it can be done).
C) is tempting, but OTOH it ends up converting a _lot_ of code to raw just
because there is one raw user, this strips the validation/tracing off for all
the other users.
So we pick B) and declare any code that ends up doing:
raw_local_irq_save()
local_irq_save()
lockdep_assert_irqs_disabled();
broken. AFAICT this problem has existed forever, the only reason it came
up is because commit: 859d069ee1dd ("lockdep: Prepare for NMI IRQ
state tracking") changed IRQ tracing vs lockdep recursion and the
first instance is fairly common, the other cases hardly ever happen.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[rewrote changelog]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Marco Elver <elver@google.com>
Link: https://lkml.kernel.org/r/20200723105615.1268126-1-npiggin@gmail.com
---
arch/powerpc/include/asm/hw_irq.h | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
(limited to 'arch')
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) \
--
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