MIME-Version: 1.0
In-Reply-To: <20110311024731.GB26122@google.com>
References: <20110307021127.GB31188@google.com> <alpine.LFD.2.00.1103082114270.2787@localhost6.localdomain6>
 <20110309112550.GA3050@google.com> <alpine.LFD.2.00.1103101948540.2787@localhost6.localdomain6>
 <20110311021654.GA26122@google.com> <20110311024731.GB26122@google.com>
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sun, 13 Mar 2011 15:49:15 -0700
Message-ID: <AANLkTinXxCMVozx-NKEVXJLNrB1V93VEAJ8FiHQHXY_=@mail.gmail.com>
Subject: Re: [PATCH 1/3] futex: do not pagefault_disable in futex_atomic_cmpxchg_inatomic()
To: Michel Lespinasse <walken@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Darren Hart <darren@dvhart.com>,
        Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <peterz@infradead.org>,
        Matt Turner <mattst88@gmail.com>,
        Russell King <linux@arm.linux.org.uk>,
        David Howells <dhowells@redhat.com>, Tony Luck <tony.luck@intel.com>,
        Michal Simek <monstr@monstr.eu>, Ralf Baechle <ralf@linux-mips.org>,
        "James E.J. Bottomley" <jejb@parisc-linux.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Paul Mundt <lethal@linux-sh.org>,
        "David S. Miller" <davem@davemloft.net>,
        Chris Metcalf <cmetcalf@tilera.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset=ISO-8859-1
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1596
Lines: 36

On Thu, Mar 10, 2011 at 6:47 PM, Michel Lespinasse <walken@google.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@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/