Re: [tip:sched/urgent] sched: Fix __schedule_bug() output when calledfrom an interrupt

From: Chris Metcalf
Date: Thu Mar 29 2012 - 09:39:59 EST

On 3/29/2012 3:16 AM, tip-bot for Stephen Boyd wrote:
> Commit-ID: 6135fc1eb4b1c9ae5f535507ed59591bab51e630
> Gitweb:
> 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:
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>

Acked-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>

We have been using this same exact patch internally for a while now, and by
a curious fluke of timing, I sent email to Ingo and to Satyam Sharma
pointing out that we really should re-look at the original change just
yesterday :-)

Chris Metcalf, Tilera Corp.

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