Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754738Ab0DTNwk (ORCPT ); Tue, 20 Apr 2010 09:52:40 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:36386 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754073Ab0DTNwi (ORCPT ); Tue, 20 Apr 2010 09:52:38 -0400 Date: Tue, 20 Apr 2010 06:52:27 -0700 From: "Paul E. McKenney" To: Miles Lane Cc: Eric Paris , Lai Jiangshan , Ingo Molnar , Peter Zijlstra , LKML Subject: Re: [PATCH] RCU: don't turn off lockdep when find suspicious rcu_dereference_check() usage Message-ID: <20100420135227.GC2628@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1271098032.4807.137.camel@twins> <1271242058.32749.19.camel@laptop> <1271701612.2972.5.camel@dhcp231-113.rdu.redhat.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5245 Lines: 143 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/