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 19:49:43 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: Yazen Ghannam <yazen.ghannam@....com>, Borislav Petkov <bp@...en8.de>,
	"Naik, Avadhut" <avadnaik@....com>, "Paul E . McKenney" <paulmck@...nel.org>
CC: "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

I said:

>          spin_lock(&pool->lock);
>          list_add_rcu(&chunk->next_chunk, &pool->chunks);
>          spin_unlock(&pool->lock);

Avadhut said:

> gen_pool_alloc_algo_owner() iterates over the existing chunks
> within the genpool through list_for_each_entry_rcu(), within
> an RCU read-side critical section (rcu_read_lock()).
 

> So the concern is not about traversal, but rather that the #MC can break the
> list_add_rcu(). Is this correct?

Yazen,

Yes. The question is whether a #MC that come in the middle of list_rcu_add()
can safely do list_for_each_entry_rcu() on the same list.

RCU is black magic ... maybe it can do this? Adding Paul.

-Tony