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Date: Tue, 26 May 2015 21:22:45 -0400
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Subject: Re: [PATCH 000/208] big x86 FPU code rewrite
From: Bobby Powers <bobbypowers@gmail.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Kernel development list <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Thomas Gleixner <tglx@linutronix.de>
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Hello,

Ingo Molnar <mingo@kernel.org> wrote:
> Please have a look.

I've been running this for ~ 2 weeks.  I've only seen one issue, when
emerging mesa 10.5.6:

[May26 20:41] traps: aclocal-1.15[27452] trap invalid opcode
ip:7f6331031ab0 sp:7ffe73ece880 error:0 in
libperl.so.5.20.2[7f6330f18000+19e000]
[  +0.000051] ------------[ cut here ]------------
[  +0.000005] WARNING: CPU: 0 PID: 27452 at
arch/x86/kernel/fpu/core.c:324 fpu__activate_stopped+0x8a/0xa0()
[  +0.000002] Modules linked in: bnep iwlmvm btusb btintel bluetooth iwlwifi
[  +0.000007] CPU: 0 PID: 27452 Comm: aclocal-1.15 Not tainted 4.1.0-rc5+ #163
[  +0.000001] Hardware name: LENOVO 20BSCTO1WW/20BSCTO1WW, BIOS
N14ET24W (1.02 ) 10/27/2014
[  +0.000001]  ffffffff82172735 ffff88017cccb998 ffffffff81c4f534
0000000080000000
[  +0.000002]  0000000000000000 ffff88017cccb9d8 ffffffff8112611a
ffff88017cccb9f8
[  +0.000002]  ffff88018e352400 0000000000000000 0000000000000000
ffff8801ef813a00
[  +0.000002] Call Trace:
[  +0.000004]  [<ffffffff81c4f534>] dump_stack+0x4f/0x7b
[  +0.000003]  [<ffffffff8112611a>] warn_slowpath_common+0x8a/0xc0
[  +0.000003]  [<ffffffff8112620a>] warn_slowpath_null+0x1a/0x20
[  +0.000002]  [<ffffffff81059c9a>] fpu__activate_stopped+0x8a/0xa0
[  +0.000002]  [<ffffffff8105a221>] xfpregs_get+0x31/0x90
[  +0.000001]  [<ffffffff8105bcc9>] ? getreg+0xa9/0x130
[  +0.000003]  [<ffffffff812ba121>] elf_core_dump+0x531/0x1490
[  +0.000003]  [<ffffffff812c3671>] do_coredump+0xbd1/0xef0
[  +0.000004]  [<ffffffff81150238>] ? try_to_wake_up+0x1f8/0x350
[  +0.000002]  [<ffffffff81134a4c>] get_signal+0x38c/0x700
[  +0.000003]  [<ffffffff8104dbb8>] do_signal+0x28/0x760
[  +0.000002]  [<ffffffff8104e92d>] ? do_trap+0x6d/0x150
[  +0.000002]  [<ffffffff8126246e>] ? vfs_read+0x11e/0x140
[  +0.000003]  [<ffffffff8152f481>] ? trace_hardirqs_off_thunk+0x17/0x19
[  +0.000002]  [<ffffffff8104e360>] do_notify_resume+0x70/0x80
[  +0.000002]  [<ffffffff81c58d82>] retint_signal+0x42/0x80
[  +0.000002] ---[ end trace 8baea2e2110d6ca1 ]---

This trace is a bit off - the path to fpu__activate_stopped from
elf_core_dump looks like:

fpu__activate_stopped
xfgregs_get
fill_thread_core_info
fill_note_info
elf_core_dump

It looks like the WARN_ON_FPU there is just invalid?  If we're
dumping, we have a valid case for curr == target.

I can reproduce this and I have the coredump, but I have no hope in
creating a test case out of this.

yours,
Bobby