Re: [PATCH v3 4/6] x86/MCE: Make number of MCA banks per_cpu

From: Borislav Petkov
Date: Tue May 21 2019 - 16:31:10 EST

On Tue, May 21, 2019 at 05:52:42PM +0000, Ghannam, Yazen wrote:
> This message comes from ___might_sleep() which checks the
> system_state.
> On CPU0, system_state=SYSTEM_BOOTING.
> On every other CPU, system_state=SYSTEM_SCHEDULING, and that's the
> only system_state where the message is shown.

Right, the check in ___might_sleep().

> Changing GFP_KERNEL to GFP_ATOMIC seems to be a fix. Is this
> appropriate? Or do you think there's something else we could try?

From: Documentation/core-api/memory-allocation.rst

* If you think that accessing memory reserves is justified and the kernel
will be stressed unless allocation succeeds, you may use ``GFP_ATOMIC``.

I don't think the MCA banks representation justifies accessing memory

Can we do instead:

-static DEFINE_PER_CPU_READ_MOSTLY(struct mce_bank *, mce_banks_array);
+static DEFINE_PER_CPU_READ_MOSTLY(struct mce_bank, mce_banks_array[MAX_NR_BANKS]);

which should be something like 9*32 = 288 bytes per CPU.

Unless you have a better idea...



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