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Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake to not use wait-queues

From Oleg Nesterov <oleg@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake to not use wait-queues
Date 2016-12-05 12:50 +0100
Message-ID <sKZWp-3YN-1@gated-at.bofh.it> (permalink)
References <sEWye-2tW-9@gated-at.bofh.it> <sEWye-2tW-29@gated-at.bofh.it> <sK85H-3yk-1@gated-at.bofh.it> <sKWYx-2e2-17@gated-at.bofh.it> <sKZD4-3S7-5@gated-at.bofh.it>
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On 12/05, Oleg Nesterov wrote:
>
> Yes, but on a second thought task_rcu_dereference() won't really help,

I forgot to explain why, see below.

> 	#define xxx_wait_event(xxx, event) {
> 		// comment to explain why
> 		WARN_ON(current->exit_state);

Otherwise this process/thread can be already (auto)reaped and wakeup
can't rely on rcu.

And task_rcu_dereference() can't help because it can return NULL in
this case.

Oleg.

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Thread

[PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake to not  use wait-queues Davidlohr Bueso <dave@stgolabs.net> - 2016-12-03 03:20 +0100
  Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake to  not use wait-queues Peter Zijlstra <peterz@infradead.org> - 2016-12-05 09:40 +0100
    Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake         to not use wait-queues Oleg Nesterov <oleg@redhat.com> - 2016-12-05 12:30 +0100
      Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake         to not use wait-queues Oleg Nesterov <oleg@redhat.com> - 2016-12-05 12:50 +0100
      Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake to  not use wait-queues Davidlohr Bueso <dave@stgolabs.net> - 2016-12-05 18:40 +0100
    Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake         to not use wait-queues Oleg Nesterov <oleg@redhat.com> - 2016-12-05 18:20 +0100
  Re: [PATCH v2 2/3] locking/percpu-rwsem: Rework writer block/wake         to not use wait-queues Oleg Nesterov <oleg@redhat.com> - 2016-12-05 18:20 +0100

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