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Date: Wed, 6 Jun 2007 01:00:28 +0400
From: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@linux-foundation.org>,
       Ulrich Drepper <drepper@redhat.com>
Subject: Re: [RFC][PATCH] muptiple bugs in PI futexes
Message-ID: <20070605210028.GA10084@ms2.inr.ac.ru>
References: <20070507144351.GA12302@ms2.inr.ac.ru> <20070523072609.GC6859@elte.hu> <20070523115159.GA30251@ms2.inr.ac.ru> <1181060711.4404.114.camel@chaos> <20070605173949.GA27618@ms2.inr.ac.ru> <1181069306.4404.145.camel@chaos> <1181070953.4404.149.camel@chaos>
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Hello!

> We actually need to do something about this, as we might loop for ever
> there. The robust cleanup code can fail (e.g. due to list corruption)
> and we would see exit_state != 0 and the OWNER_DIED bit would never be
> set, so we are stuck in a busy loop.

Yes...

It is possible to take read_lock(&tasklist_lock) before:

        inc_preempt_count();
        curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
        dec_preempt_count();

and drop it after lookup_pi_state().

In this case exiting task will set FUTEX_OWNER_DIED, but will
spin in exit_notify(), we will find valid pi_state and go slow path
taking rtmutex.

Alexey
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