lockdep: Print a nicer description for irq inversion bugs
authorSteven Rostedt <srostedt@redhat.com>
Thu, 21 Apr 2011 01:41:57 +0000 (21:41 -0400)
committerIngo Molnar <mingo@elte.hu>
Fri, 22 Apr 2011 09:06:58 +0000 (11:06 +0200)
commitdad3d7435e1d8c254d6877dc06852dc00c5da812
tree85f4ab38ff63879b117d363ef1fdb3cf83bf870d
parent48702ecf308e53f176c1f6fdc193d622ded54ac0
lockdep: Print a nicer description for irq inversion bugs

Irq inversion and irq dependency bugs are only subtly
different. The diffenerence lies where the interrupt occurred.

For irq dependency:

irq_disable
lock(A)
lock(B)
unlock(B)
unlock(A)
irq_enable

lock(B)
unlock(B)

  <interrupt>
  lock(A)

The interrupt comes in after it has been established that lock A
can be held when taking an irq unsafe lock. Lockdep detects the
problem when taking lock A in interrupt context.

With the irq_inversion the irq happens before it is established
and lockdep detects the problem with the taking of lock B:

  <interrupt>
  lock(A)

irq_disable
lock(A)
lock(B)
unlock(B)
unlock(A)
irq_enable

lock(B)
unlock(B)

Since the problem with the locking logic for both of these issues
is in actuality the same, they both should report the same scenario.
This patch implements that and prints this:

other info that might help us debug this:

Chain exists of:
  &rq->lock --> lockA --> lockC

 Possible interrupt unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(lockC);
                               local_irq_disable();
                               lock(&rq->lock);
                               lock(lockA);
  <Interrupt>
    lock(&rq->lock);

 *** DEADLOCK ***

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110421014259.910720381@goodmis.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
kernel/lockdep.c