lkml.org 
[lkml]   [2024]   [Feb]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 2/2] x86/MCE: Add command line option to extend MCE Records pool
From
On 2/11/2024 6:14 AM, Borislav Petkov wrote:
> On Sat, Feb 10, 2024 at 03:15:26PM -0600, Naik, Avadhut wrote:
>> IIUC, you wouldn't want to extend the pool through late_initcall().
>> Instead, you would want for memory to be allocated (on the heap) and
>> size of the pool to be set at the very beginning i.e. when the pool
>> is created (~2 seconds, according to dmesg timestamps).
>>
>> Please correct me if I have understood wrong.
>
> Nah, you got it right. I went, looked and realized that we have to do
> this early dance because we have no allocator yet. And we can't move
> this gen_pool allocation to later, when we *do* have an allocator
> because MCA is up and logging already.
>
> But your extending approach doesn't fly in all cases either:
>
> gen_pool_add->gen_pool_add_virt->gen_pool_add_owner
>
> it grabs the pool->lock spinlock and adds to &pool->chunks while, at the
> exact same time, gen_pool_alloc(), in *NMI* context iterates over that
> same &pool->chunks in the case we're logging an MCE at exact that same
> time when you're extending the buffer.
>
> And Tony already said that in the thread you're quoting:
>
> https://lore.kernel.org/linux-edac/SJ1PR11MB60832922E4D036138FF390FAFCD7A@SJ1PR11MB6083.namprd11.prod.outlook.com/
>
> So no, that doesn't work either.
>

I'm confused why it won't work.

X86 has ARCH_HAVE_NMI_SAFE_CMPXCHG. I expect atomics/caches will still
work in interrupt or #MC context. If not, then we'd have a fatal error
that causes a hardware reset or a kernel panic before we get to logging,
I think.

Or is the issue when running on the same CPU? In this case, either
&pool->chunks was updated before taking the #MC, so the extra memory
is there and can be used. Or it wasn't updated, so the extra memory is
not available during the #MC which is the same behavior as now.

I need to look more at the genpool code, but I thought I'd ask too.

Thanks,
Yazen





\
 
 \ /
  Last update: 2024-05-27 14:59    [W:0.152 / U:0.080 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site