linux-kernel - Re: [PATCH] disable softlockup detection at boottime

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Date:	Mon, 28 Apr 2008 13:52:52 -0500
From:	Dimitri Sivanich <sivanich@....com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] disable softlockup detection at boottime

On Mon, Apr 28, 2008 at 06:55:44PM +0200, Ingo Molnar wrote:
> 
> good idea - but why dont you set softlockup_thresh to 0, which is the 
> "off" switch already? (and that way it can be turned back on later as 
> well, by the sysadmin.)
> 

I'm getting unaligned access errors trying to set it to anything, so it's not working for me currently (2.6.25):

It's tripping up on the address of 'one', which is an int that is not properly aligned for the unsigned long comparison in proc_doulongvec_minmax on my 64 bit machine.  Also, the value '0' is invalid for softlockup_thresh, correct?

I temporarily got around these issues with the following hack.

Index: linux/kernel/sysctl.c
===================================================================
--- linux.orig/kernel/sysctl.c  2008-04-16 21:49:44.000000000 -0500
+++ linux/kernel/sysctl.c       2008-04-28 13:37:43.000561710 -0500
@@ -748,9 +748,9 @@ static struct ctl_table kern_table[] = {
                .data           = &softlockup_thresh,
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
-               .proc_handler   = &proc_doulongvec_minmax,
+               .proc_handler   = &proc_dointvec_minmax,
                .strategy       = &sysctl_intvec,
-               .extra1         = &one,
+               .extra1         = &zero,
                .extra2         = &sixty,



Also, I'm not convinced that changing this to 0 does indeed switch off softlockup detection (but I could be missing something):

void softlockup_tick(void)
{
..
..
        /* Warn about unreasonable delays: */
        if (now <= (touch_timestamp + softlockup_thresh))
                return;
        
        per_cpu(print_timestamp, this_cpu) = touch_timestamp;
   
        spin_lock(&print_lock);
        printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
                        this_cpu, now - touch_timestamp,
                        current->comm, task_pid_nr(current));


Dimitri
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