From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754868Ab2E2RyJ (ORCPT ); Tue, 29 May 2012 13:54:09 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44633 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754545Ab2E2RyH (ORCPT ); Tue, 29 May 2012 13:54:07 -0400 Date: Tue, 29 May 2012 13:53:53 -0400 From: Don Zickus To: Russ Anderson Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Morton , Greg Kroah-Hartman Subject: Re: [PATCH] x86: Avoid intermixing cpu dump_stack output on multi-processor systems Message-ID: <20120529175352.GA31524@redhat.com> References: <20120524144229.GA27713@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120524144229.GA27713@sgi.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 24, 2012 at 09:42:29AM -0500, Russ Anderson wrote: > When multiple cpus on a multi-processor system call dump_stack() > at the same time, the backtrace lines get intermixed, making > the output worthless. Add a lock so each cpu stack dump comes > out as a coherent set. > > For example, when a multi-processor system is NMIed, all of the > cpus call dump_stack() at the same time, resulting in output for > all of cpus getting intermixed, making it impossible to tell what > any individual cpu was doing. With this patch each cpu prints > its stack lines as a coherent set, so one can see what each cpu > was doing. For this particular test case, it sounds like you are doing what trigger_all_cpu_backtrace() is doing? It doesn't solve the general problem, but probably your particular usage? Cheers, Don > > It has been tested on a 4069 cpu system. > > Signed-off-by: Russ Anderson > > --- > arch/x86/kernel/dumpstack.c | 3 +++ > 1 file changed, 3 insertions(+) > > Index: linux/arch/x86/kernel/dumpstack.c > =================================================================== > --- linux.orig/arch/x86/kernel/dumpstack.c 2012-05-03 14:31:13.602345805 -0500 > +++ linux/arch/x86/kernel/dumpstack.c 2012-05-03 14:51:43.805197563 -0500 > @@ -186,7 +186,9 @@ void dump_stack(void) > { > unsigned long bp; > unsigned long stack; > + static DEFINE_SPINLOCK(lock); /* Serialise the printks */ > > + spin_lock(&lock); > bp = stack_frame(current, NULL); > printk("Pid: %d, comm: %.20s %s %s %.*s\n", > current->pid, current->comm, print_tainted(), > @@ -194,6 +196,7 @@ void dump_stack(void) > (int)strcspn(init_utsname()->version, " "), > init_utsname()->version); > show_trace(NULL, NULL, &stack, bp); > + spin_unlock(&lock); > } > EXPORT_SYMBOL(dump_stack); > > -- > Russ Anderson, OS RAS/Partitioning Project Lead > SGI - Silicon Graphics Inc rja@sgi.com > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/