Date:	Wed, 10 Dec 2014 16:51:26 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Rik van Riel <riel@...hat.com>
Cc:	Daniel J Blueman <daniel@...ra.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH, 3.18] sleeping function called from invalid context

On Wed, Dec 10, 2014 at 4:49 PM, Rik van Riel <riel@...hat.com> wrote:
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> On 12/10/2014 07:46 PM, Daniel J Blueman wrote:
>> Gah. I had some non-temporal copy changes in the wrong tree. I'll
>> check with a definitely clean tree and follow up if it still
>> occurs.
>
> The exception handlers should definitely allow sleeping,
> so I suspect those changes may be related.

It would be really, really nice if we could arrange for
kernel_fpu_begin to be unconditionally usable in anything except NMI
context.  The crypto code would be much less scary, we could make
non-temporal copies safe, etc.  Can we have ponies, too?

--Andy

>
>> On 10 December 2014 at 16:37, Andy Lutomirski <luto@...capital.net>
>> wrote:
>>> Adding Rik, who is probably the most recent person to have looked
>>> at the disaster fondly known as "FPU".
>>>
>>> On Wed, Dec 10, 2014 at 4:25 PM, Daniel J Blueman
>>> <daniel@...ra.org> wrote:
>>>> With 3.18, I was seeing a significant number of allocation
>>>> warnings from load_elf_binary call paths [1].
>>>>
>>>> Allocating FPU state atomically [2] does prevent potentially
>>>> sleeping while atomic, but probably isn't the correct fix.
>>>> Anyone familiar with this area?
>>>>
>>>> -- [1]
>>>>
>>>> BUG: sleeping function called from invalid context at
>>>> mm/slub.c:1240 in_atomic(): 1, irqs_disabled(): 0, pid: 29016,
>>>> name: dmesg INFO: lockdep is turned off. Preemption disabled
>>>> at:[<ffffffff8114625f>] handle_mm_fault+0x5ff/0x8a0
>>>>
>>>> CPU: 122 PID: 29016 Comm: dmesg Tainted: G        W
>>>> 3.18.0-test #6 Hardware name: Supermicro AS -1042G-LTF/H8QGL,
>>>> BIOS DS3.5a     11/13/2014 ffffffff8203b81b ffff886fdf62f888
>>>> ffffffff81b942e8 0000000000000007 0000000000000000
>>>> ffff886fdf62f8b8 ffffffff8109ac4c 0000000000000000
>>>> 0000000000000010 ffff8807df84bc00 00000000000000d0
>>>> ffff886fdf62f908 Call Trace: [<ffffffff81b942e8>]
>>>> dump_stack+0x4f/0x7c [<ffffffff8109ac4c>]
>>>> __might_sleep+0x164/0x250 [<ffffffff8116372b>]
>>>> kmem_cache_alloc+0xeb/0x138 [<ffffffff8100e0e1>]
>>>> init_fpu+0x71/0xb0 [<ffffffff81003966>]
>>>> math_state_restore+0xce/0x208 [<ffffffff8100437b>]
>>>> do_device_not_available+0x2b/0x60 [<ffffffff81ba70f5>]
>>>> device_not_available+0x15/0x20 [<ffffffff81487102>] ?
>>>> copy_page+0x12/0x33
>>>
>>> wtf?  I don't see any fpu state being accessed in copy_page.
>>>
>>> Can you disassemble "[<ffffffff81487102>] ?
>>> copy_page+0x12/0x33"?
>>>
>>> --Andy
>>>
>>>> [<ffffffff8109edb9>] ? get_parent_ip+0x11/0x58
>>>> [<ffffffff8109ee55>] ? preempt_count_add+0x55/0xb0
>>>> [<ffffffff811437a1>] ? do_cow_fault+0xe9/0x258
>>>> [<ffffffff8114625f>] handle_mm_fault+0x5ff/0x8a0
>>>> [<ffffffff81032218>] ? __do_page_fault+0xc8/0x498
>>>> [<ffffffff811481b9>] ? vma_gap_callbacks_rotate+0x19/0x20
>>>> [<ffffffff8103227d>] __do_page_fault+0x12d/0x498
>>>> [<ffffffff810b682e>] ? up_write+0x1e/0x48 [<ffffffff81148d18>]
>>>> ? vma_link+0x80/0xc0 [<ffffffff81149cb2>] ?
>>>> vma_set_page_prot+0x3a/0x60 [<ffffffff8114ae6e>] ?
>>>> mmap_region+0x1be/0x5e0 [<ffffffff8103262e>]
>>>> do_page_fault+0x1e/0x70 [<ffffffff81ba737f>]
>>>> page_fault+0x1f/0x30 [<ffffffff81487f3e>] ?
>>>> __clear_user+0x2e/0x50 [<ffffffff81487f22>] ?
>>>> __clear_user+0x12/0x50 [<ffffffff81487f8a>]
>>>> clear_user+0x2a/0x30 [<ffffffff811ca1e1>] padzero+0x21/0x30
>>>> [<ffffffff811cc41f>] load_elf_binary+0x8cf/0xdd0
>>>> [<ffffffff8117d18f>] search_binary_handler+0x7f/0x1f8
>>>> [<ffffffff8117ec06>] do_execve_common.isra.34+0x616/0x790
>>>> [<ffffffff8117eb62>] ? do_execve_common.isra.34+0x572/0x790
>>>> [<ffffffff8117ed93>] do_execve+0x13/0x18 [<ffffffff8117f070>]
>>>> SyS_execve+0x20/0x30 [<ffffffff81ba6159>]
>>>> stub_execve+0x69/0xa0
>>>>
>>>> -- [2]
>>>>
>>>> diff --git a/arch/x86/include/asm/fpu-internal.h
>>>> b/arch/x86/include/asm/fpu-internal.h index e97622f..57029ad
>>>> 100644 --- a/arch/x86/include/asm/fpu-internal.h +++
>>>> b/arch/x86/include/asm/fpu-internal.h @@ -574,7 +574,7 @@
>>>> static inline int fpu_alloc(struct fpu *fpu) { if
>>>> (fpu_allocated(fpu)) return 0; -       fpu->state =
>>>> kmem_cache_alloc(task_xstate_cachep, GFP_KERNEL); +
>>>> fpu->state = kmem_cache_alloc(task_xstate_cachep, GFP_ATOMIC);
>>>> if (!fpu->state) return -ENOMEM; WARN_ON((unsigned
>>>> long)fpu->state & 15); -- Daniel J Blueman
>>>
>>>
>>>
>>> -- Andy Lutomirski AMA Capital Management, LLC
>>
>>
>>
>
>
> - --
> All rights reversed
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-- 
Andy Lutomirski
AMA Capital Management, LLC
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