linux-kernel - Re: [PATCH RESEND] Fix a dead loop in async_synchronize

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Message-Id: <20120711154232.165cbca9.akpm@linux-foundation.org>
Date:	Wed, 11 Jul 2012 15:42:32 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Li Zhong <zhong@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, arjan@...ux.intel.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christian Kujau <lists@...dbynature.de>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH RESEND] Fix a dead loop in async_synchronize_full()

On Mon, 09 Jul 2012 15:04:25 +0800
Li Zhong <zhong@...ux.vnet.ibm.com> wrote:

> This patch tries to fix a dead loop in  async_synchronize_full(), which
> could be seen when preemption is disabled on a single cpu machine. 
> 
> void async_synchronize_full(void)
> {
>         do {
>                 async_synchronize_cookie(next_cookie);
>         } while (!list_empty(&async_running) || !
> list_empty(&async_pending));
> }
> 
> async_synchronize_cookie() calls async_synchronize_cookie_domain() with
> &async_running as the default domain to synchronize. 
> 
> However, there might be some works in the async_pending list from other
> domains. On a single cpu system, without preemption, there is no chance
> for the other works to finish, so async_synchronize_full() enters a dead
> loop. 
> 
> It seems async_synchronize_full() wants to synchronize all entries in
> all running lists(domains), so maybe we could just check the entry_count
> to know whether all works are finished. 
> 
> Currently, async_synchronize_cookie_domain() expects a non-NULL running
> list ( if NULL, there would be NULL pointer dereference ), so maybe a
> NULL pointer could be used as an indication for the functions to
> synchronize all works in all domains. 

The patch is fairly wordwrapped - please fix up your email client.

More seriously, it does not apply to linux-next due to some fairly
significant changes which have been sitting in Dan's tree since May. 
What's going on?

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