From: Oleg Nesterov <oleg@redhat.com>
To: Matt Fleming <matt@console-pimps.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: __lock_task_sighand() and RCU
Date: Mon, 28 Mar 2011 15:36:02 +0200 [thread overview]
Message-ID: <20110328133602.GA8612@redhat.com> (raw)
In-Reply-To: <20110328085654.26a75db6@mfleming-mobl1.ger.corp.intel.com>
Hi Matt,
On 03/28, Matt Fleming wrote:
>
> I've been reading __lock_task_sighand() and I can't quite wrap my head
> around what the rcu_read_lock()/rcu_read_unlock() is protecting in
> there.
It protects ->sighand.
> Initially I assumed that it was protecting the 'tsk' argument,
No. the caller must have a reference.
> Then I wondered if it was protecting the sighand from being freed from
> under us while we're trying to lock it.
Yes,
> But sighands aren't freed via
> rcu,
it is ;)
> it's just a simple refcnt and kmem_cache_free()
Yes, but please note that sighand_cachep was created with
SLAB_DESTROY_BY_RCU.
Oleg.
next prev parent reply other threads:[~2011-03-28 14:45 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-28 7:56 __lock_task_sighand() and RCU Matt Fleming
2011-03-28 13:36 ` Oleg Nesterov [this message]
2011-03-28 15:04 ` Matt Fleming
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