linux-kernel - Re: Yet more softlockups.

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Message-ID: <51E03F76.3090607@gmail.com>
Date:	Fri, 12 Jul 2013 11:40:06 -0600
From:	David Ahern <dsahern@...il.com>
To:	Dave Jones <davej@...hat.com>, Dave Hansen <dave.hansen@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Peter Anvin <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: Yet more softlockups.

On 7/12/13 11:18 AM, Dave Jones wrote:
> On Fri, Jul 12, 2013 at 11:12:13AM -0600, David Ahern wrote:
>   > On 7/12/13 9:45 AM, Dave Jones wrote:
>   > > Here's a fun trick:
>   > >
>   > > trinity -c perf_event_open -C4 -q -l off
>   > >
>   > > Within about a minute, that brings any of my boxes to its knees.
>   > > The softlockup detector starts going nuts, and then the box wedges solid.
>   >
>   > I tried that in a VM running latest Linus tree. I see trinity children
>   > getting nuked regularly from oom.
>
> Weird. I'm curious what the backtrace looks like in those cases.
> Where is it trying to allocate memory ?
> (Though that isn't usually too helpful in most cases, but in absense of
>   anything else..)

(gdb) bt
#0  0x000000313b27f3e0 in malloc () from /lib64/libc.so.6
#1  0x0000000000404405 in _get_address 
(null_allowed=null_allowed@...ry=1 '\001') at generic-sanitise.c:151
#2  0x00000000004044ca in get_address () at generic-sanitise.c:182
#3  0x00000000004052a0 in fill_arg (childno=<optimized out>, 
call=call@...ry=298, argnum=argnum@...ry=1) at generic-sanitise.c:415
#4  0x000000000040548d in generic_sanitise (childno=childno@...ry=0) at 
generic-sanitise.c:615
#5  0x0000000000405620 in mkcall (childno=childno@...ry=0) at syscall.c:131
#6  0x0000000000407d85 in child_process () at child.c:219
#7  0x00000000004073ad in fork_children () at main.c:103
#8  main_loop () at main.c:308
#9  do_main_loop () at main.c:342
#10 0x000000000040253a in main (argc=<optimized out>, argv=<optimized 
out>) at trinity.c:180


In _get_address, case 8 must be happening a lot and I don't see a free 
when that address comes from malloc. Perhaps all of the rand() calls are 
breaking down in the VM. If I change that case from malloc to something 
static - like page_rand - memory stays flat.

David
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