Re: [PATCH 0/1] futex: check PF_KTHREAD rather than !p->mm to filter out kthreads

From: Darren Hart <darren@dvhart.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jerome Marchand <jmarchan@redhat.com>,
	Larry Woodman <lwoodman@redhat.com>,
	Mateusz Guzik <mguzik@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	dvhart@infradead.org
Subject: Re: [PATCH 0/1] futex: check PF_KTHREAD rather than !p->mm to filter out kthreads
Date: Mon, 9 Feb 2015 12:38:41 -0800	[thread overview]
Message-ID: <CAGChsmOLYCDfjQQquZ_jd5gX+zUKxoojK0cr5AvedUgNL=pNMQ@mail.gmail.com> (raw)
In-Reply-To: <20150206170425.GA7493@redhat.com>

Hi Oleg, Peter,

Wow! When it rains it pours.

I'm paging this all in, but unfortunately, like both of you, I'm
pretty new to the robust futexes side of this problem.

I will prepare the test that Peter suggested so we have something to
test with now as well as run for regressions over time.

On Fri, Feb 6, 2015 at 9:04 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> Peter, I am spamming you again and again, but I didn't even start the
> patches. It turns out I can do nothing until devconf.cz finishes next
> week.
>
> On 02/06, Peter Zijlstra wrote:
>>
>> On Thu, Feb 05, 2015 at 07:10:14PM +0100, Oleg Nesterov wrote:
>>
>> > So I think that in this case we either need to recheck that *uaddr is still the
>> > same (and turn -ESRCH into -EAGAIN otherwise), or change handle_futex_death() to
>> > serialize with X so that it can proceed and attach pi_state.
>> >
>> > No?
>>
>> I _think_ you're right, doing -ESRCH is wrong without first looking to
>> see if uval changed and gained an FUTEX_OWNER_DIED.
>

Hrm, if we cleared the TID mask, and the pi chain is empty, can we not
clear the waiters? I'm sure there's at least one corner case that
complicates this further... I'll think on this more and get back to
you.

-- 
Darren Hart