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Date: Wed, 19 Aug 2015 08:15:21 +0200
From: Ingo Molnar <mingo@kernel.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Juergen Gross <jgross@suse.com>, Andy Lutomirski <luto@kernel.org>,
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        Brian Gerst <brgerst@gmail.com>, Denys Vlasenko <dvlasenk@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [GIT PULL] x86 fixes
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* Ingo Molnar <mingo@kernel.org> wrote:

> So I went and built 743aa456c1834f76 with ARCH=i386 defconfig +MATH_EMULATION=y 
> and booted it on real hardware with and without 'no387':
> 
>   - 743aa456c1834f76:         boots fine to a generic distro
>   - 743aa456c1834f76 + no387: early crash
> 
> the early crash is similar to what I saw when doing the recent FPU changes (and 
> which crash I fixed):

Hm, so that crash is back again with the latest kernel:

[    0.000000] EIP is at kmem_cache_alloc+0x25/0x110                                                                                                                                  
...
[    0.000000]  [<c020a11f>] init_fpu+0x7f/0xc0                                                                                                                                       
[    0.000000]  [<c0730df5>] math_emulate+0x6b5/0xc90                                                                                                                                 
[    0.000000]  [<c0227440>] ? early_serial_putc+0x60/0x60                                                                                                                            
[    0.000000]  [<c02359cc>] ? call_console_drivers.constprop.14+0x8c/0xe0                                                                                                            
[    0.000000]  [<c0258c05>] ? up+0x25/0x50                                                                                                                                           
[    0.000000]  [<c02366e5>] ? console_unlock+0x305/0x4d0                                                                                                                             
[    0.000000]  [<c0258b06>] ? process_srcu+0x56/0xb0                                                                                                                                 
[    0.000000]  [<c08b0d20>] ? do_debug+0x160/0x160                                                                                                                                   
[    0.000000]  [<c08b0d58>] do_device_not_available+0x38/0x60                                                                                                                        
[    0.000000]  [<c08b0752>] error_code+0x5a/0x60                                                                                                                                     
[    0.000000]  [<c08b0d20>] ? do_debug+0x160/0x160                                                                                                                                   
[    0.000000]  [<c08a29e7>] ? fpu_init+0xd9/0xf7                                                                                                                                     
[    0.000000]  [<c08a475e>] cpu_init+0x237/0x23f                                                                                                                                     
[    0.000000]  [<c0b324f2>] trap_init+0x243/0x24b                                                                                                                                    
[    0.000000]  [<c0b30759>] start_kernel+0x143/0x2d4                                                                                                                                 
[    0.000000]  [<c0b302a0>] i386_start_kernel+0x76/0x7b                        

I suspect due to:

  5aaeb5c01c5b x86/fpu, sched: Introduce CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT and use it on x86
  0c8c0f03e3a2 x86/fpu, sched: Dynamically allocate 'struct fpu'

Thanks,

	Ingo