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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Eric Wong <normalperson@yhbt.net>
Cc: "Arve Hjønnevåg" <arve@android.com>, NeilBrown <neilb@suse.de>,
	"Rafael J. Wysocki" <rjw@sisk.pl>,
	linux-kernel@vger.kernel.org,
	"Davide Libenzi" <davidel@xmailserver.org>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org,
	"Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: epoll: possible bug from wakeup_source activation
Date: Sun, 10 Mar 2013 05:59:37 +0100	[thread overview]
Message-ID: <1362891577.4051.21.camel@edumazet-glaptop> (raw)
In-Reply-To: <20130310011136.GA4815@dcvr.yhbt.net>

On Sun, 2013-03-10 at 01:11 +0000, Eric Wong wrote:
>  
>  static void ep_destroy_wakeup_source(struct epitem *epi)
>  {
> -	wakeup_source_unregister(epi->ws);
> -	epi->ws = NULL;
> +	struct wakeup_source *ws = epi->ws;
> +
> +	rcu_assign_pointer(epi->ws, NULL);

There is no need to use a memory barrier before setting epi->ws to NULL

You should use RCU_POINTER_INIT()

> +	synchronize_rcu(); /* wait for ep_pm_stay_awake to finish */

Wont this add a significant slowdown ?

> +	wakeup_source_unregister(ws);
>  }

Please add the following in your .config

CONFIG_SPARSE_RCU_POINTER=y

and try :

make C=2 fs/eventpoll.o

And fix all warnings ;)




  reply	other threads:[~2013-03-10  4:59 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-03-07 11:26 Eric Wong
2013-03-08  1:30 ` Eric Wong
2013-03-08  4:56   ` Arve Hjønnevåg
2013-03-08 20:49     ` Eric Wong
2013-03-09  4:09       ` Arve Hjønnevåg
2013-03-09  7:10         ` Eric Wong
2013-03-10  1:11           ` Eric Wong
2013-03-10  4:59             ` Eric Dumazet [this message]
2013-03-10 11:50               ` [PATCH] epoll: use RCU protect wakeup_source in epitem Eric Wong
2013-03-14  3:09                 ` [PATCH mm] epoll: lock ep->mtx in ep_free to silence lockdep Eric Wong
2013-03-11 23:37           ` epoll: possible bug from wakeup_source activation Arve Hjønnevåg
2013-03-12  0:17             ` Eric Wong
2013-03-12  0:29               ` Arve Hjønnevåg
2013-03-12  0:44                 ` Eric Wong

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