linux-kernel - Re: [PATCH 2/2] lockdep: check that no locks held at freeze time

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Message-ID: <20130504130440.GC13770@amd.pavel.ucw.cz>
Date:	Sat, 4 May 2013 15:04:40 +0200
From:	Pavel Machek <pavel@....cz>
To:	Colin Cross <ccross@...roid.com>
Cc:	linux-kernel@...r.kernel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mandeep Singh Baines <msb@...omium.org>,
	Paul Walmsley <paul@...an.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-nfs@...r.kernel.org,
	linux-pm@...r.kernel.org, netdev@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Ben Chan <benchan@...omium.org>
Subject: Re: [PATCH 2/2] lockdep: check that no locks held at freeze time

On Fri 2013-05-03 14:04:10, Colin Cross wrote:
> From: Mandeep Singh Baines <msb@...omium.org>
> 
> We shouldn't try_to_freeze if locks are held.  Holding a lock can cause a
> deadlock if the lock is later acquired in the suspend or hibernate path
> (e.g.  by dpm).  Holding a lock can also cause a deadlock in the case of
> cgroup_freezer if a lock is held inside a frozen cgroup that is later
> acquired by a process outside that group.

Ok, but this does not explain why

> --- a/include/linux/debug_locks.h
> +++ b/include/linux/debug_locks.h
> @@ -51,7 +51,7 @@ struct task_struct;
>  extern void debug_show_all_locks(void);
>  extern void debug_show_held_locks(struct task_struct *task);
>  extern void debug_check_no_locks_freed(const void *from, unsigned long len);
> -extern void debug_check_no_locks_held(struct task_struct *task);
> +extern void debug_check_no_locks_held(void);
>  #else
>  static inline void debug_show_all_locks(void)
>  {

Removing task_struct argument from  those functions is good idea?

> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -835,7 +835,7 @@ void do_exit(long code)
>  	/*
>  	 * Make sure we are holding no locks:
>  	 */
> -	debug_check_no_locks_held(tsk);
> +	debug_check_no_locks_held();

Is task guaranteed == current?

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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