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

From: Stephen Boyd
Date: Wed Mar 28 2012 - 20:10:51 EST

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@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>

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)

@@ -3113,11 +3111,7 @@ static noinline void __schedule_bug(struct task_struct *prev)
if (irqs_disabled())
- 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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