linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CA+55aFyQzpQgT91sqpEhXho8KoVRkA1MeRjk+fXO7w2dJkY_Gg@mail.gmail.com>
Date:	Sat, 20 Dec 2014 13:16:29 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Dave Jones <davej@...hat.com>, Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Suresh Siddha <sbsiddha@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Anvin <hpa@...ux.intel.com>
Subject: Re: frequent lockups in 3.18rc4

On Sat, Dec 20, 2014 at 10:25 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> How/where is the HPET overflow case handled? I don't know the code enough.

Hmm, ok, I've re-acquainted myself with it. And I have to admit that I
can't see anything wrong. The whole "update_wall_clock" and the shadow
timekeeping state is confusing as hell, but seems fine. We'd have to
avoid update_wall_clock for a *long* time for overflows to occur.

And the overflow in 32 bits isn't that special, since the only thing
that really matters is the overflow of "cycle_now - tkr->cycle_last"
within the mask.

So I'm not seeing anything even halfway suspicious.

                  Linus
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