linux-kernel - Re: [PATCH 2/2] x86/MCE: Add command line option to extend MCE Records pool

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Date: Mon, 12 Feb 2024 14:46:57 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: "Luck, Tony" <tony.luck@...el.com>,
	Yazen Ghannam <yazen.ghannam@....com>,
	"Naik, Avadhut" <avadnaik@....com>,
	"Mehta, Sohil" <sohil.mehta@...el.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Avadhut Naik <avadhut.naik@....com>
Subject: Re: [PATCH 2/2] x86/MCE: Add command line option to extend MCE
 Records pool

On Mon, Feb 12, 2024 at 10:27:41PM +0100, Borislav Petkov wrote:
> On Mon, Feb 12, 2024 at 12:44:06PM -0800, Paul E. McKenney wrote:
> > If it is the #MC adding new memory, agreed.
> > 
> > If the #MC is simply traversing the list, and the interrupted context
> > was in the midst of adding a new element, this should be no worse than
> > some other CPU traversing the list while this CPU is in the midst of
> > adding a new element.
> 
> Right, Tony answered which context is doing what.
> 
> What I'm still scratching my head over is, why grab a spinlock around
> 
> 	list_add_rcu(&chunk->next_chunk, &pool->chunks);
> 
> ?
> 
> That's the part that looks really weird.
> 
> And that's the interrupted context, yap.

The usual reason is to exclude other CPUs also doing list_add_rcu()
on the same list.  Or is there other synchronization that is preventing
concurrent updates?

							Thanx, Paul