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Date: Thu, 10 Mar 2016 14:48:09 +0200
Message-ID: <CAHp75Vetx62afSZXLT96C02s=eXLZSap5poYnMUsMEZ=UfcFqw@mail.gmail.com>
Subject: Re: Got FPU related warning on Intel Quark during boot
From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>, Borislav Petkov <bp@alien8.de>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Oleg Nesterov <oleg@redhat.com>,
        "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
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On Thu, Mar 10, 2016 at 1:19 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> I've Cc:-ed more FPU developers. Mail quoted below. I don't have a Quark system to
> test this on, but maybe others have an idea why this warning triggers?
>
> My thinking is that it's related to:
>
>   58122bf1d856 x86/fpu: Default eagerfpu=on on all CPUs

He-he, my cursor stays on
        if (!use_eager_fpu() || !static_cpu_has(X86_FEATURE_FPU)) {
while I was having a lunch. So far got from datasheet that some kind
of FPU is present there.

eagerfpu=auto doesn't fix
eagerfpu=off fixes the issue

>> Today tried first time after long break to boot Intel Quark SoC with
>> most recent linux-next. Got the following warning:
>>
>> [   14.714533] WARNING: CPU: 0 PID: 823 at
>> arch/x86/include/asm/fpu/internal.h:163 fpu__clear+0x8c/0x160
>> [   14.726603] Modules linked in:
>> [   14.729910] CPU: 0 PID: 823 Comm: kworker/u2:0 Not tainted
>> 4.5.0-rc7-next-20160310+ #137
>> [   14.738307]  00000000 00000000 ce691e20 c12b6fc9 ce691e50 c1049fd1
>> c1978c6c 00000000
>> [   14.747000]  00000337 c196b530 000000a3 c102050c 000000a3 ce587ac0
>> 00000000 ce653000
>> [   14.755722]  ce691e64 c104a095 00000009 00000000 00000000 ce691e74
>> c102050c ce587500
>> [   14.764468] Call Trace:
>> [   14.767172]  [<c12b6fc9>] dump_stack+0x16/0x1d
>> [   14.771889]  [<c1049fd1>] __warn+0xd1/0xf0
>> [   14.776253]  [<c102050c>] ? fpu__clear+0x8c/0x160
>> [   14.781234]  [<c104a095>] warn_slowpath_null+0x25/0x30
>> [   14.786648]  [<c102050c>] fpu__clear+0x8c/0x160
>> [   14.791447]  [<c101f347>] flush_thread+0x57/0x60
>> [   14.796341]  [<c113a5cc>] flush_old_exec+0x4cc/0x600
>> [   14.801594]  [<c117ab20>] load_elf_binary+0x2b0/0x1060
>> [   14.807010]  [<c1111220>] ? get_user_pages_remote+0x50/0x60
>> [   14.812898]  [<c12c4687>] ? _copy_from_user+0x37/0x40
>> [   14.818236]  [<c1139f82>] search_binary_handler+0x62/0x150
>> [   14.824007]  [<c113b19c>] do_execveat_common+0x45c/0x600
>> [   14.829647]  [<c113b35f>] do_execve+0x1f/0x30
>> [   14.834289]  [<c1059941>] call_usermodehelper_exec_async+0x91/0xe0
>> [   14.840765]  [<c17f2310>] ret_from_kernel_thread+0x20/0x40
>> [   14.846540]  [<c10598b0>] ? umh_complete+0x40/0x40
>> [   14.851626] ---[ end trace 137ff5893f9b85bf ]---
>>
>> Is it know issue? Or what could I try to fix it?
>>
>> Reproducibility:  3 of 3.

-- 
With Best Regards,
Andy Shevchenko