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Date: Sun, 15 Dec 2013 20:33:45 +0100
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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To: Ben Hutchings <ben@decadent.org.uk>
CC: Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Steven Rostedt <rostedt@rostedt.homelinux.com>, 723180@bugs.debian.org,
        Brian Silverman <bsilver16384@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: Double fault when single-stepping compat task with PREEMPT_RT
References: <20130917061329.4872.51468.reportbug@dell-inspiron-linux.dlinkrouter>  <1379427451.23881.48.camel@deadeye.wl.decadent.org.uk>  <CAP01z6LVxoA6kDJeL8NuO2aA22BjMvXSk9ZY7z9cOK1=k56vpg@mail.gmail.com>  <1379905562.3913.8.camel@deadeye.wl.decadent.org.uk>  <CAP01z6+j6moUio9pc3G3iz+ebJCdKEvngddxnxazRP+NXwLkyg@mail.gmail.com> <1380115449.4430.21.camel@deadeye.wl.decadent.org.uk>
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On 09/25/2013 03:24 PM, Ben Hutchings wrote:
> On Tue, 2013-09-24 at 13:43 -0700, Brian Silverman wrote: [...]
>> I got down to a really simple program that reproduces this bug:
>> 
>> 
>> #include <sys/syscall.h> #include <unistd.h> int main() { // I've
>> tried SYS_getpid, SYS_write, and SYS_read here too. 
>> syscall(SYS_gettid); }

Brian, thank you for this excellent stripped down test case.
I think I know what is going on, will dig more later.

> Ben.
> 

Sebastian