From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757522Ab0EBCAq (ORCPT ); Sat, 1 May 2010 22:00:46 -0400 Received: from mail-ww0-f46.google.com ([74.125.82.46]:47620 "EHLO mail-ww0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754770Ab0EBCAp convert rfc822-to-8bit (ORCPT ); Sat, 1 May 2010 22:00:45 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=fo/bThiukt/ILK1tuus0N805AYFMW7A3a0B7opLXwKGYGF/EJlEKz8BsXYyTFwJguo Tb9HT3xmAs5PSTmg+tdPfFsZtfgesi7MCZYtfMWnhTeC1fnNybfHMgrLK1VpjiJy1Hzl zWIV/vm9PbJklN7uUtn93vsI0LIs8q1d/3QrY= MIME-Version: 1.0 In-Reply-To: <20100501215502.GA2474@linux.vnet.ibm.com> References: <1271242058.32749.19.camel@laptop> <20100419230136.GA16856@linux.vnet.ibm.com> <1271726729.2972.13.camel@dhcp231-113.rdu.redhat.com> <20100420030452.GB2905@linux.vnet.ibm.com> <4BCD646B.1080206@cn.fujitsu.com> <1271766716.2972.16.camel@dhcp231-113.rdu.redhat.com> <20100420135227.GC2628@linux.vnet.ibm.com> <20100501215502.GA2474@linux.vnet.ibm.com> Date: Sat, 1 May 2010 22:00:43 -0400 Message-ID: Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage From: Miles Lane To: paulmck@linux.vnet.ibm.com Cc: Eric Paris , Lai Jiangshan , Ingo Molnar , Peter Zijlstra , LKML Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 1, 2010 at 5:55 PM, Paul E. McKenney wrote: > On Sat, May 01, 2010 at 01:26:15PM -0400, Miles Lane wrote: >> On Tue, Apr 20, 2010 at 9:52 AM, Paul E. McKenney >> wrote: >> > On Tue, Apr 20, 2010 at 08:45:28AM -0400, Miles Lane wrote: >> >> Is there a patch set for 2.6.34-rc5 I can test? >> > >> > I will be sending a patchset out later today after testing, but >> > please see below for a sneak preview collapsed into a single patch. >> > >> >                                                        Thanx, Paul >> > >> >> On Tue, Apr 20, 2010 at 8:31 AM, Eric Paris wrote: >> >> >> >> > On Tue, 2010-04-20 at 16:23 +0800, Lai Jiangshan wrote: >> >> > >> >> > > [PATCH] RCU: don't turn off lockdep when find suspicious >> >> > rcu_dereference_check() usage >> >> > > >> >> > > When suspicious rcu_dereference_check() usage is detected, lockdep is >> >> > still >> >> > > available actually, so we should not call debug_locks_off() in >> >> > > lockdep_rcu_dereference(). >> >> > > >> >> > > For get rid of too much "suspicious rcu_dereference_check() usage" >> >> > > output when the "if(!debug_locks_off())" statement is removed. This patch >> >> > uses >> >> > > static variable '__warned's for very usage of "rcu_dereference*()". >> >> > > >> >> > > One variable per usage, so, Now, we can get multiple complaint >> >> > > when we detect multiple different suspicious rcu_dereference_check() >> >> > usage. >> >> > > >> >> > > Requested-by: Eric Paris >> >> > > Signed-off-by: Lai Jiangshan >> >> > >> >> > Although mine was a linux-next kernel and it doesn't appear that I have >> >> > rcu_dereference_protected() at all, so I dropped that bit of the patch, >> >> > it worked great!  I got 4 more complaints to harass people with.  Feel >> >> > free to add my tested by if you care to. >> >> > >> >> > Tested-by: Eric Paris >> > >> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h >> > index 07db2fe..ec9ab49 100644 >> > --- a/include/linux/rcupdate.h >> > +++ b/include/linux/rcupdate.h >> > @@ -190,6 +190,15 @@ static inline int rcu_read_lock_sched_held(void) >> > >> >  #ifdef CONFIG_PROVE_RCU >> > >> > +#define __do_rcu_dereference_check(c)                                  \ >> > +       do {                                                            \ >> > +               static bool __warned;                                   \ >> > +               if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \ >> > +                       __warned = true;                                \ >> > +                       lockdep_rcu_dereference(__FILE__, __LINE__);    \ >> > +               }                                                       \ >> > +       } while (0) >> > + >> >  /** >> >  * rcu_dereference_check - rcu_dereference with debug checking >> >  * @p: The pointer to read, prior to dereferencing >> > @@ -219,8 +228,7 @@ static inline int rcu_read_lock_sched_held(void) >> >  */ >> >  #define rcu_dereference_check(p, c) \ >> >        ({ \ >> > -               if (debug_lockdep_rcu_enabled() && !(c)) \ >> > -                       lockdep_rcu_dereference(__FILE__, __LINE__); \ >> > +               __do_rcu_dereference_check(c); \ >> >                rcu_dereference_raw(p); \ >> >        }) >> > >> > @@ -237,8 +245,7 @@ static inline int rcu_read_lock_sched_held(void) >> >  */ >> >  #define rcu_dereference_protected(p, c) \ >> >        ({ \ >> > -               if (debug_lockdep_rcu_enabled() && !(c)) \ >> > -                       lockdep_rcu_dereference(__FILE__, __LINE__); \ >> > +               __do_rcu_dereference_check(c); \ >> >                (p); \ >> >        }) >> > >> > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c >> > index da5e139..e5c0244 100644 >> > --- a/kernel/cgroup_freezer.c >> > +++ b/kernel/cgroup_freezer.c >> > @@ -205,9 +205,12 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task) >> >         * No lock is needed, since the task isn't on tasklist yet, >> >         * so it can't be moved to another cgroup, which means the >> >         * freezer won't be removed and will be valid during this >> > -        * function call. >> > +        * function call.  Nevertheless, apply RCU read-side critical >> > +        * section to suppress RCU lockdep false positives. >> >         */ >> > +       rcu_read_lock(); >> >        freezer = task_freezer(task); >> > +       rcu_read_unlock(); >> > >> >        /* >> >         * The root cgroup is non-freezable, so we can skip the >> > diff --git a/kernel/lockdep.c b/kernel/lockdep.c >> > index 2594e1c..03dd1fa 100644 >> > --- a/kernel/lockdep.c >> > +++ b/kernel/lockdep.c >> > @@ -3801,8 +3801,6 @@ void lockdep_rcu_dereference(const char *file, const int line) >> >  { >> >        struct task_struct *curr = current; >> > >> > -       if (!debug_locks_off()) >> > -               return; >> >        printk("\n===================================================\n"); >> >        printk(  "[ INFO: suspicious rcu_dereference_check() usage. ]\n"); >> >        printk(  "---------------------------------------------------\n"); >> > diff --git a/kernel/sched.c b/kernel/sched.c >> > index 6af210a..14c44ec 100644 >> > --- a/kernel/sched.c >> > +++ b/kernel/sched.c >> > @@ -323,6 +323,15 @@ static inline struct task_group *task_group(struct task_struct *p) >> >  /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */ >> >  static inline void set_task_rq(struct task_struct *p, unsigned int cpu) >> >  { >> > +       /* >> > +        * Strictly speaking this rcu_read_lock() is not needed since the >> > +        * task_group is tied to the cgroup, which in turn can never go away >> > +        * as long as there are tasks attached to it. >> > +        * >> > +        * However since task_group() uses task_subsys_state() which is an >> > +        * rcu_dereference() user, this quiets CONFIG_PROVE_RCU. >> > +        */ >> > +       rcu_read_lock(); >> >  #ifdef CONFIG_FAIR_GROUP_SCHED >> >        p->se.cfs_rq = task_group(p)->cfs_rq[cpu]; >> >        p->se.parent = task_group(p)->se[cpu]; >> > @@ -332,6 +341,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu) >> >        p->rt.rt_rq  = task_group(p)->rt_rq[cpu]; >> >        p->rt.parent = task_group(p)->rt_se[cpu]; >> >  #endif >> > +       rcu_read_unlock(); >> >  } >> > >> >  #else >> > >> >> Hi Paul. >> >> Has this patch made it into the Linus tree? >> Thanks! > > Hello, Miles, > > Not yet -- working with Ingo to get a variant of it into -tip on > its way to Linus's tree.  The latest patch stack may be found at > http://lkml.org/lkml/2010/4/30/500. > >                                                Thanx, Paul > What is the rationale for defaulting to showing only one RCU splat? That setting seems likely to reduce the rate at which things get cleaned up. Ciao, Miles