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SubjectRe: kvm_intel: Could not allocate 42 bytes percpu data
On 6/30/2013 11:22 PM, Rusty Russell wrote:
> Chegu Vinod <chegu_vinod@hp.com> writes:
>> Hello,
>>
>> Lots (~700+) of the following messages are showing up in the dmesg of a
>> 3.10-rc1 based kernel (Host OS is running on a large socket count box
>> with HT-on).
>>
>> [ 82.270682] PERCPU: allocation failed, size=42 align=16, alloc from
>> reserved chunk failed
>> [ 82.272633] kvm_intel: Could not allocate 42 bytes percpu data
> Woah, weird....
>
> Oh. Shit. Um, this is embarrassing.
>
> Thanks,
> Rusty.


Thanks for your response!

> ===
> module: do percpu allocation after uniqueness check. No, really!
>
> v3.8-rc1-5-g1fb9341 was supposed to stop parallel kvm loads exhausting
> percpu memory on large machines:
>
> Now we have a new state MODULE_STATE_UNFORMED, we can insert the
> module into the list (and thus guarantee its uniqueness) before we
> allocate the per-cpu region.
>
> In my defence, it didn't actually say the patch did this. Just that
> we "can".
>
> This patch actually *does* it.
>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> Tested-by: Noone it seems.

Your following "updated" fix seems to be working fine on the larger
socket count machine with HT-on.

Thx
Vinod
>
> diff --git a/kernel/module.c b/kernel/module.c
> index cab4bce..fa53db8 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2927,7 +2927,6 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
> {
> /* Module within temporary copy. */
> struct module *mod;
> - Elf_Shdr *pcpusec;
> int err;
>
> mod = setup_load_info(info, flags);
> @@ -2942,17 +2941,10 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
> err = module_frob_arch_sections(info->hdr, info->sechdrs,
> info->secstrings, mod);
> if (err < 0)
> - goto out;
> + return ERR_PTR(err);
>
> - pcpusec = &info->sechdrs[info->index.pcpu];
> - if (pcpusec->sh_size) {
> - /* We have a special allocation for this section. */
> - err = percpu_modalloc(mod,
> - pcpusec->sh_size, pcpusec->sh_addralign);
> - if (err)
> - goto out;
> - pcpusec->sh_flags &= ~(unsigned long)SHF_ALLOC;
> - }
> + /* We will do a special allocation for per-cpu sections later. */
> + info->sechdrs[info->index.pcpu].sh_flags &= ~(unsigned long)SHF_ALLOC;
>
> /* Determine total sizes, and put offsets in sh_entsize. For now
> this is done generically; there doesn't appear to be any
> @@ -2963,17 +2955,22 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
> /* Allocate and move to the final place */
> err = move_module(mod, info);
> if (err)
> - goto free_percpu;
> + return ERR_PTR(err);
>
> /* Module has been copied to its final place now: return it. */
> mod = (void *)info->sechdrs[info->index.mod].sh_addr;
> kmemleak_load_module(mod, info);
> return mod;
> +}
>
> -free_percpu:
> - percpu_modfree(mod);
> -out:
> - return ERR_PTR(err);
> +static int alloc_module_percpu(struct module *mod, struct load_info *info)
> +{
> + Elf_Shdr *pcpusec = &info->sechdrs[info->index.pcpu];
> + if (!pcpusec->sh_size)
> + return 0;
> +
> + /* We have a special allocation for this section. */
> + return percpu_modalloc(mod, pcpusec->sh_size, pcpusec->sh_addralign);
> }
>
> /* mod is no longer valid after this! */
> @@ -3237,6 +3234,11 @@ static int load_module(struct load_info *info, const char __user *uargs,
> }
> #endif
>
> + /* To avoid stressing percpu allocator, do this once we're unique. */
> + err = alloc_module_percpu(mod, info);
> + if (err)
> + goto unlink_mod;
> +
> /* Now module is in final location, initialize linked lists, etc. */
> err = module_unload_init(mod);
> if (err)
> .
>



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