Re: [PATCH, 3.18] sleeping function called from invalid context

[Andy Lutomirski]

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@xxxxxxxxx> 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
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