linux-kernel - Re: [PATCH 1/3] futex: do not pagefault_disable in futex_atomic_cmpxchg

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <AANLkTinXxCMVozx-NKEVXJLNrB1V93VEAJ8FiHQHXY_=@mail.gmail.com>
Date:	Sun, 13 Mar 2011 15:49:15 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Darren Hart <darren@...art.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Matt Turner <mattst88@...il.com>,
	Russell King <linux@....linux.org.uk>,
	David Howells <dhowells@...hat.com>,
	Tony Luck <tony.luck@...el.com>,
	Michal Simek <monstr@...str.eu>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Metcalf <cmetcalf@...era.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] futex: do not pagefault_disable in futex_atomic_cmpxchg_inatomic()

On Thu, Mar 10, 2011 at 6:47 PM, Michel Lespinasse <walken@...gle.com> wrote:
> kernel/futex.c disables page faults before calling
> futex_atomic_cmpxchg_inatomic(), so there is no need to do it again
> within that function.

This seems totally bogus.

Even the comment is crap.

Sure, the callers may disable preemption, but that has NOTHING to do
with "pagefault_disable()". Th epagefault_[en/dis]able functions will
touch the preempt count EVEN IF PREEMPTION ISN'T EVEN ENABLED!

So what the f*ck does that "Note that preemption is disabled.." crap even mean?

The thing is made even worse by the fact that as far as I can tell,
the comment simply isn't true at all (even if you were to ignore the
fundamental confusion about preemption vs the pagefault
disable/enable). Not all callers of futex_atomic_cmpxchg_inatomic() do
anything of the sort, whether it's preemptibility _or_ the proper
pagefault_disable/enable(). Just look at the exit_robust_list() ->
handle_futex_death(), for example.

This kind of patch is the kind that personally makes me want to put
you on a spam-list. Misleading commit messages with bogus and
fundamentally incorrect added comments in the code. WTF?

Did I miss some patch that changed that, or is this really as horribly
bad as I think it is? I see it already made it into -tip.

                              Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/