Messages in this thread | | | Date | Mon, 12 Feb 2024 13:47:14 -0500 | Subject | Re: [PATCH 2/2] x86/MCE: Add command line option to extend MCE Records pool | From | Yazen Ghannam <> |
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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
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