linux-kernel - Re: [PATCH 0/4 V3] Print traces on softlockup

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Message-Id: <20140423123550.1818553bcdff3ef058efd3f7@linux-foundation.org>
Date:	Wed, 23 Apr 2014 12:35:50 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Don Zickus <dzickus@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	davem@...emloft.net, sparclinux@...r.kernel.org, mguzik@...hat.com
Subject: Re: [PATCH 0/4 V3] Print traces on softlockup

On Wed, 23 Apr 2014 15:22:28 -0400 Don Zickus <dzickus@...hat.com> wrote:

> On Tue, Apr 22, 2014 at 11:28:28AM -0700, Andrew Morton wrote:
> > On Tue, 22 Apr 2014 11:17:24 -0400 Don Zickus <dzickus@...hat.com> wrote:
> > 
> > > Added more patches to handle the 'uniprocessor' panic case by sending NMIs
> > > to every cpu but self.  Only affects x86, sparc.
> > > 
> > 
> > Looks OK to me.  A couple of things:
> > 
> > - Patches 1-3 should be combined so we don't create bisection holes
> >   due to x86 and sparc build errors.
> > 
> > - Patch 4 adds stuff which is unusable on uniprocessor, especially
> >   the presence of /proc/sys/kernel/softlockup_all_cpu_backtrace.  We
> >   already have #ifdef CONFIG_SMP in kern_table, so do more of that?
> 
> Are you suggesting just add CONFIG_SMP to kern_table entry or all the
> pieces in kernel/watchdog.c too?  I wasn't sure how messy I should make
> this patch.

Well, don't go nuts and be tasteful. 

/proc/sys/kernel/softlockup_all_cpu_backtrace should disappear.

Look around for existing #ifdef CONFIG_SMP blocks to use.

Making sysctl_softlockup_all_cpu_backtrace evaluate to literal zero
will cause the compiler to remove unused code without ifdefs.  This
might require that watchdog_timer_fn:softlockup_all_cpu_backtrace (why
does this local exist btw) be declared const - check the compiler
output.

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