On Wed, 2010-07-07 at 07:03 -0700, Darren Hart wrote:
> On 07/07/2010 04:57 AM, Thomas Gleixner wrote:
> > Cc'ing Darren.
> >
> > On Wed, 7 Jul 2010, Mike Galbraith wrote:
> >
>
> Hi Mike,
>
> >> Greetings,
> >>
> >> Stress testing, looking to trigger RCU stalls, I've managed to find a
> >> way to repeatably create fireworks. (got RCU stall, see attached)
> >>
> >> 1. download ltp-full-20100630. Needs to be this version because of
> >> testcase bustage in earlier versions, and must be built with gcc> 4.3,
> >> else testcases will segfault due to a gcc bug.
>
> Interesting, I had not hit any gcc specific issues with this. Can you
> point me to the bug?
gcc-4.3 doesn't grok volatile inside a struct. Workaround below.
Index: ltp-full-20090930/testcases/realtime/include/librttest.h
===================================================================
--- ltp-full-20090930.orig/testcases/realtime/include/librttest.h
+++ ltp-full-20090930/testcases/realtime/include/librttest.h
@@ -88,7 +88,7 @@ struct thread {
int flags;
int id;
};
-typedef struct { volatile int counter; } atomic_t;
+typedef volatile struct { volatile int counter; } atomic_t;
// flags for threads
#define THREAD_START 1
> >> --- run.sh.org 2010-07-06 15:54:58.000000000 +0200
> >> +++ run.sh 2010-07-06 16:37:34.000000000 +0200
> >> @@ -22,7 +22,7 @@ make
> >> # process to run realtime. The remainder of the processes (if any)
> >> # will run non-realtime in any case.
> >>
> >> -nthread=5000
> >> +nthread=500
>
> Was this just to lighten the load, or was it required to reproduce?
Just to lighten it.
> Which architecture?
x64_64.
> Glibc version?
glibc-2.11.2-2.3
> I see kernel version is: 2.6.33.6-rt23, have you reproduced this on
> earlier kernel versions as well? Any 2.6.31 rt kernel would be a good
> data point.
Yes, both 2.6.31.14-rt21 and 2.6.29.6-rt24.
> Is this immediately reproducible for you?
Yes, nearly instant kaboom.
> I see a possibly fault occuring in the stack, if you run with
> mlockall(), does the problem go away? (assuming not, but an easy thing
> to test).
Nope, -m made no difference.
-Mike
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