From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Stefan Liebler <stli@linux.ibm.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Darren Hart <dvhart@infradead.org>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [patch] futex: Cure exit race
Date: Tue, 18 Dec 2018 10:31:06 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.21.1812172239090.1660@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20181212090418.GT5289@hirez.programming.kicks-ass.net>
On Wed, 12 Dec 2018, Peter Zijlstra wrote:
> On Mon, Dec 10, 2018 at 06:43:51PM +0100, Thomas Gleixner wrote:
> @@ -806,6 +806,8 @@ void __noreturn do_exit(long code)
> * task into the wait for ever nirwana as well.
> */
> tsk->flags |= PF_EXITPIDONE;
> + smp_mb();
> + wake_up_bit(&tsk->flags, 3 /* PF_EXITPIDONE */);
Using ilog2(PF_EXITPIDONE) spares that horrible inline comment and more
importantly selects the right bit. 0x04 is bit 2 ....
> @@ -1187,10 +1236,15 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key,
> * set, we know that the task has finished the
> * cleanup:
> */
> int ret = handle_exit_race(uaddr, uval, p);
>
> raw_spin_unlock_irq(&p->pi_lock);
> - put_task_struct(p);
> +
> + if (ret == -EAGAIN)
> + *pe = p;
Hmm, no. We really want to split the return value for that. EAGAIN is also
returned for other reasons.
Plus requeue_pi() needs the same treatment. I'm staring into it, but all I
came up with so far is horribly ugly.
Thanks,
tglx
next prev parent reply other threads:[~2018-12-18 9:31 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-10 15:23 [patch] futex: Cure exit race Thomas Gleixner
2018-12-10 16:02 ` Peter Zijlstra
2018-12-10 17:43 ` Thomas Gleixner
2018-12-12 9:04 ` Peter Zijlstra
2018-12-18 9:31 ` Thomas Gleixner [this message]
2018-12-19 13:29 ` Thomas Gleixner
2018-12-19 19:13 ` Thomas Gleixner
[not found] ` <20181210210920.75EBD20672@mail.kernel.org>
2018-12-10 21:16 ` Thomas Gleixner
2018-12-10 23:01 ` Sasha Levin
2018-12-11 10:29 ` Thomas Gleixner
2018-12-11 8:04 ` Stefan Liebler
2018-12-11 10:32 ` Thomas Gleixner
2018-12-18 22:18 ` [tip:locking/urgent] " tip-bot for Thomas Gleixner
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