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Date: Mon, 20 Aug 2012 17:58:04 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Jones <davej@redhat.com>, Linux Kernel <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, rostedt <rostedt@goodmis.org>,
        dhowells <dhowells@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: lockdep trace from posix timers
Message-ID: <20120820155804.GA21400@redhat.com>
References: <20120724203613.GA9637@redhat.com> <1345140478.29668.54.camel@twins> <20120817151447.GA7918@redhat.com> <1345446957.23018.14.camel@twins> <1345463081.23018.34.camel@twins> <20120820145919.GB18499@redhat.com> <1345475434.23018.48.camel@twins> <1345476436.23018.54.camel@twins> <20120820153225.GA20258@redhat.com> <1345477609.23018.61.camel@twins>
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On 08/20, Peter Zijlstra wrote:
>
> On Mon, 2012-08-20 at 17:32 +0200, Oleg Nesterov wrote:
>
> > > I guess we could steal the entire list and requeue it afterwards and
> > > lift TIF_NOTIFY_RESUME along with it..
> >
> > We can't. This can race with exit_task_work(). And this can break
> > fput(), the task can return to the userspace without __fput().
>
> So we could put that spinlock back around cancel and run and leave add
> lockless. That'd solve my immediate problem but its not something I'm
> proud of.

Which problem?

We can probably use bit_spin_lock() and avoid ->pi_lock.

Of course, we can add the new lock into task_struct, but this is not nice.

Oleg.