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Date: Fri, 31 Jul 2015 12:51:17 -0400
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
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To: Andy Lutomirski <luto@amacapital.net>
CC: Andy Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
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        Jan Beulich <jbeulich@suse.com>, xen-devel <xen-devel@lists.xen.org>,
        stable <stable@vger.kernel.org>
Subject: Re: [PATCH v5 2/4] x86/ldt: Make modify_ldt synchronous
References: <cover.1438061139.git.luto@kernel.org> <1f1e8e0367408585694132a0e8693d157959ce30.1438061139.git.luto@kernel.org> <55BA6534.2080407@oracle.com> <CALCETrXqT3zeJUX9uyjDGOdUi0dHUGwBn-n2NOaPaFpmB2pmDg@mail.gmail.com> <55BA6E6B.7040102@oracle.com> <CALCETrX7ppxZ5_9hbGwFx7fxe_60t8xVamg62f1Xghi8a68urg@mail.gmail.com>
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On 07/30/2015 03:25 PM, Andy Lutomirski wrote:
> On Thu, Jul 30, 2015 at 11:35 AM, Boris Ostrovsky
> <boris.ostrovsky@oracle.com> wrote:
>> [OK]    LDT entry 0 has AR 0x0040F200 and limit 0x00000000
>> [OK]    LDT entry 0 is invalid
>> [RUN]   Cross-CPU LDT invalidation
>> Segmentation fault (core dumped)
> That's not good.
>
> Can you backtrace it?  (I.e. compite ldt_gdt_32 with -g and load the
> core dumb in gdb?)  My best guesses are either a signal delivery
> failure (although that shouldn't be a problem for 32-bit userspace on
> any kernel) or an actual LDT access fault, and the latter would be
> interesting.
>
> I haven't been able to reproduce this.

This looks like a userspace bug. Breaks on F18, works fine in F22.

Possibly something about signal handling --- I noticed on F18 I'd get 
two SEGV's in a row whereas we should only get one.

Anyway, this is not an issue as far as this thread is concerned.

-boris