From: Oleg Nesterov <oleg@redhat.com>
To: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Salman Qazi <sqazi@google.com>,
linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
Roland McGrath <roland@redhat.com>, Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: A possible sys_wait* bug
Date: Thu, 1 Jul 2010 16:08:36 +0200 [thread overview]
Message-ID: <20100701140836.GA8379@redhat.com> (raw)
In-Reply-To: <20100701093621.DA24.A69D9226@jp.fujitsu.com>
On 07/01, KOSAKI Motohiro wrote:
>
> > Basically, it is possibly for readers to continuously hold
> > tasklist_lock
Yes, this is the known problem.
Perhaps do_wait() is not the worst example. sys_kill(-1),
sys_ioprio_set() scan the global list.
> > I think the most direct approach to the problem is to have the
> > readers-writer locks be writer biased (i.e. as soon as a writer
> > contends, we do not permit any new readers).
I thought about this too, but this is deadlockable. At least,
read_lock(tasklist) should nest, and it should work in irq context.
We need the more fine-grained locking, but it is not clear to me what
should be done in the long term. Afaics, this is very nontrivial.
Oleg.
next prev parent reply other threads:[~2010-07-01 14:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-05-20 20:32 A possible sys_wait* bug Salman Qazi
2010-07-01 0:47 ` KOSAKI Motohiro
2010-07-01 5:00 ` Salman Qazi
2010-07-01 5:34 ` Roland McGrath
2010-07-01 14:08 ` Oleg Nesterov [this message]
2010-07-02 6:18 ` KOSAKI Motohiro
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