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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>