[tip:sched/urgent] sched: Fix __schedule_bug() output when called from an interrupt

From: tip-bot for Stephen Boyd
Date: Thu Mar 29 2012 - 03:17:05 EST

Commit-ID: 6135fc1eb4b1c9ae5f535507ed59591bab51e630
Gitweb: http://git.kernel.org/tip/6135fc1eb4b1c9ae5f535507ed59591bab51e630
Author: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
AuthorDate: Wed, 28 Mar 2012 17:10:47 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 29 Mar 2012 08:34:45 +0200

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

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().

[ 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. ]

Also-reported-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Cc: Satyam Sharma <satyam@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1332979847-27102-1-git-send-email-sboyd@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
kernel/sched/core.c | 8 +-------
1 files changed, 1 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9c1629c..929fd85 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3099,8 +3099,6 @@ 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)

@@ -3111,11 +3109,7 @@ static noinline void __schedule_bug(struct task_struct *prev)
if (irqs_disabled())
- if (regs)
- show_regs(regs);
- else
- dump_stack();
+ dump_stack();

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