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

1 files changed, 7 insertions, 8 deletions

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 00d553d77911..3ed4e8771b64 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -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()				\