From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keith Owens <kaos@sgi.com>
Date: Thu, 29 Jan 2004 04:31:21 +0000
Subject: Re: [patch/rfc] mca ia64_log_print() race
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List-Id: <linux-ia64.vger.kernel.org>
References: <Pine.LNX.4.30.0401281942340.18291-100000@cleomedes.llnl.gov>
In-Reply-To: <Pine.LNX.4.30.0401281942340.18291-100000@cleomedes.llnl.gov>
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To: linux-ia64@vger.kernel.org

On Wed, 28 Jan 2004 19:58:33 -0800 (PST), 
Jim Garlick <garlick@llnl.gov> wrote:
>We have been exercising some of the MCA code on the bench with an instrumented
>DIMM that can generate single and multibit errors and found that fairly
>frequently the kernel would crash in the process of handling CPE's.
>
>The following patch addresses what we think is a race on ia64_state_log
>that occurs when CPE's occur back to back (as happens with our crude error
>generator, probably more than in nature), possibly exacerbated by configuring
>a slow serial console.
>
>diff -u -r1.4.2.1.4.10 -r1.4.2.1.4.15
>--- arch/ia64/kernel/mca.c      26 Jan 2004 21:18:49 -0000      1.4.2.1.4.10
>+++ arch/ia64/kernel/mca.c      29 Jan 2004 01:37:42 -0000      1.4.2.1.4.15
>@@ -2397,7 +2451,9 @@
> ia64_log_print(int sal_info_type, prfunc_t prfunc)
> {
>        int platform_err = 0;
>+       int s;

What is 's' used for?

>
>+       IA64_LOG_LOCK(sal_info_type);
>        switch(sal_info_type) {
>              case SAL_INFO_TYPE_MCA:
>                prfunc("+CPU %d: SAL log contains MCA error record\n", smp_processor_id());
>@@ -2421,6 +2477,7 @@
>                prfunc("+MCA UNKNOWN ERROR LOG (UNIMPLEMENTED)\n");
>                break;
>        }
>+       IA64_LOG_UNLOCK(sal_info_type);
>        return platform_err;
> }

That entire chunk of code has always been racy.  It is not safe to call
prfunc (printk) for any MCA or INIT events, it can deadlock and/or
break - MCA/INIT is not irq safe.  All the printing in mca.c needs to
be cleaned up.