linux-kernel - Re: [PATCH] shm: fix a race between shm_exit() and shm

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Message-ID: <CA+55aFzG+s9KvSOJHvsUczG_d66f+QbBWiWfqLC21mHswnfm-A@mail.gmail.com>
Date:	Wed, 3 Aug 2011 15:01:05 -1000
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Manuel Lauss <manuel.lauss@...glemail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Richard Weinberger <richard@....at>,
	Ingo Molnar <mingo@...e.hu>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	Kay Sievers <kay.sievers@...y.org>, Greg KH <greg@...ah.com>
Subject: Re: [PATCH] shm: fix a race between shm_exit() and shm_init()

On Wed, Aug 3, 2011 at 2:50 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> Well, it's still a workaround.  We'll still have driver_init() trying
> to run userspace helpers at an inappropriate time, and failing to do
> so.  Either something will break or it should not be attempting
> attempting to do this at all.

Well, it has never worked before either, so I wouldn't call it a
"workaround", more of a "insane subsystems do user-mode helpers for
crazy small things, and at crazy times. Stop them from wasting our
time and effort at those crazy times when we know they would fail
anyway".

> Perhaps Kay and Greg can suggest how we can fix all this up?

I think just not calling user-mode when user-mode isn't ready is a real fix.

The fact that the device models send an absolutely *insane* amount of
events for everything, and don't track "this is the bootup device
scan" on their own is kind of sad, but it's how they roll. This fixes
it at a core level, so that the device layer doesn't have to track the
"am I booting, or is this a dynamic event?" at all.

               Linus
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