On Mon, Mar 14, 2016 at 5:56 PM, Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> wrote:
> 2016-03-14 13:43 GMT+03:00 Alexander Potapenko <glider@xxxxxxxxxx>:
>
>> +
>> + rec = this_cpu_ptr(&depot_recursion);
>> + /* Don't store the stack if we've been called recursively. */
>> + if (unlikely(*rec))
>> + goto fast_exit;
>> + *rec = true;
>
>
> This just can't work. As long as preemption enabled, task could
> migrate on another cpu anytime.
Ah, you're right.
Do you think disabling preemption around memory allocation is an option here?
> You could use per-task flag, although it's possible to miss some
> in-irq stacktraces:
>
> depot_save_stack()
> if (current->stackdeport_recursion)
> goto fast_exit;
> current->stackdepot_recursion++
> <IRQ>
> ....
> depot_save_stack()
> if (current->stackdeport_recursion)
> goto fast_exit;
>
>
>
>> + if (unlikely(!smp_load_acquire(&next_slab_inited))) {
>> + /* Zero out zone modifiers, as we don't have specific zone
>> + * requirements. Keep the flags related to allocation in atomic
>> + * contexts and I/O.
>> + */
>> + alloc_flags &= ~GFP_ZONEMASK;
>> + alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
>> + /* When possible, allocate using vmalloc() to reduce physical
>> + * address space fragmentation. vmalloc() doesn't work if
>> + * kmalloc caches haven't been initialized or if it's being
>> + * called from an interrupt handler.
>> + */
>> + if (kmalloc_caches[KMALLOC_SHIFT_HIGH] && !in_interrupt()) {
>
> This is clearly a wrong way to check whether is slab available or not.
Well, I don't think either vmalloc() or kmalloc() provide any
interface to check if they are available.
> Besides you need to check
> vmalloc() for availability, not slab.
The problem was in kmalloc caches being unavailable, although I can
imagine other problems could have arose.
Perhaps we can drill a hole to get the value of vmap_initialized?
> Given that STAC_ALLOC_ORDER is 2 now, I think it should be fine to use
> alloc_pages() all the time.
> Or fix condition, up to you.
Ok, I'm going to drop vmalloc() for now, we can always implement this later.
Note that this also removes the necessity to check for recursion.
>> + prealloc = __vmalloc(
>> + STACK_ALLOC_SIZE, alloc_flags, PAGE_KERNEL);
>> + } else {
>> + page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER);
>> + if (page)
>> + prealloc = page_address(page);
>> + }
>> + }
>> +
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
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