[PATCH] sched: Fix __schedule_bug() output when called from an interrupt

* [PATCH] sched: Fix __schedule_bug() output when called from an interrupt
@ 2012-03-29  0:10 Stephen Boyd
  2012-03-29  7:16 ` [tip:sched/urgent] " tip-bot for Stephen Boyd
  0 siblings, 1 reply; 3+ messages in thread
From: Stephen Boyd @ 2012-03-29  0:10 UTC (permalink / raw)
  To: linux-kernel; +Cc: Satyam Sharma, Ingo Molnar, Peter Zijlstra

If schedule is called from an interrupt handler __schedule_bug()
will call show_regs() with the registers saved during the
interrupt handling done in do_IRQ(). This means we'll see the
registers and the backtrace for the process that was interrupted
and not the full backtrace explaining who called schedule().

This is due to 838225b (sched: use show_regs() to improve
__schedule_bug() output, 2007-10-24) which improperly assumed
that get_irq_regs() would return the registers for the current
stack because it is being called from within an interrupt
handler. Simply remove the show_reg() code so that we dump a
backtrace for the interrupt handler that called schedule().

Cc: Satyam Sharma <satyam@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---

I ran across this when I was presented with a scheduling while
atomic log with a stacktrace pointing at spin_unlock_irqrestore().
It made no sense and I had to guess what interrupt handler could
be called and poke around for someone calling schedule() in an
interrupt handler. A simple test of putting an msleep() in
an interrupt handler works better with this patch because you 
can actually see the msleep() call in the backtrace.

 kernel/sched/core.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3b4e8b7..b496a0b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3101,8 +3101,6 @@ EXPORT_SYMBOL(sub_preempt_count);
  */
 static noinline void __schedule_bug(struct task_struct *prev)
 {
-	struct pt_regs *regs = get_irq_regs();
-
 	if (oops_in_progress)
 		return;
 
@@ -3113,11 +3111,7 @@ static noinline void __schedule_bug(struct task_struct *prev)
 	print_modules();
 	if (irqs_disabled())
 		print_irqtrace_events(prev);
-
-	if (regs)
-		show_regs(regs);
-	else
-		dump_stack();
+	dump_stack();
 }
 
 /*
-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


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