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lockdep: Only trace IRQ edges

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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: 859d069ee1 ("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
This commit is contained in:
Nicholas Piggin 2020-07-23 20:56:14 +10:00 committed by Peter Zijlstra
parent 99dc56feb7
commit 044d0d6de9
2 changed files with 11 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
arch/powerpc/include/asm/hw_irq.h
View File

@ -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) \

15
include/linux/irqflags.h
View File

@ -191,25 +191,24 @@ do { \
#define local_irq_disable() \
do { \
bool was_disabled = raw_irqs_disabled();\
raw_local_irq_disable(); \
trace_hardirqs_off(); \
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() \