Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422761AbXBUSTG (ORCPT ); Wed, 21 Feb 2007 13:19:06 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422763AbXBUSTG (ORCPT ); Wed, 21 Feb 2007 13:19:06 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:39488 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422759AbXBUSTE (ORCPT ); Wed, 21 Feb 2007 13:19:04 -0500 From: "Rafael J. Wysocki" To: paulmck@linux.vnet.ibm.com Subject: Re: freezer problems Date: Wed, 21 Feb 2007 19:13:40 +0100 User-Agent: KMail/1.9.5 Cc: Oleg Nesterov , ego@in.ibm.com, akpm@osdl.org, paulmck@us.ibm.com, mingo@elte.hu, vatsa@in.ibm.com, dipankar@in.ibm.com, venkatesh.pallipadi@intel.com, linux-kernel@vger.kernel.org, Pavel Machek References: <20070214144031.GA15257@in.ibm.com> <200702201929.03776.rjw@sisk.pl> <20070221181404.GC7063@linux.vnet.ibm.com> In-Reply-To: <20070221181404.GC7063@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200702211913.41883.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5525 Lines: 156 On Wednesday, 21 February 2007 19:14, Paul E. McKenney wrote: > On Tue, Feb 20, 2007 at 07:29:01PM +0100, Rafael J. Wysocki wrote: > > On Tuesday, 20 February 2007 01:32, Rafael J. Wysocki wrote: > > > On Tuesday, 20 February 2007 01:12, Oleg Nesterov wrote: > > > Hm. In the case discussed above we have a task that's right before calling > > > frozen_process(), so we can't thaw it, because it's not frozen. It will be > > > frozen just in a while, but try_to_freeze_tasks() and thaw_tasks() have no > > > way to check this. > > > > > > I think to close this race the refrigerator should check TIF_FREEZE and set > > > PF_FROZEN _and_ reset TIF_FREEZE under a lock that would also have to be > > > taken by try_to_freeze_tasks() in the beginning of the error path. This will > > > ensure that all tasks either freeze themselves before the error path in > > > try_to_freeze_tasks() is executed, or remain unfrozen. > > > > > > I'll try to prepare a patch to illustrate this, but right now I'm too tired to > > > do it. :-) > > > > Something like this, perhaps: > > > > --- > > include/linux/freezer.h | 10 +++------- > > kernel/power/process.c | 18 ++++++++++++++++-- > > 2 files changed, 19 insertions(+), 9 deletions(-) > > > > Index: linux-2.6.20-mm2/include/linux/freezer.h > > =================================================================== > > --- linux-2.6.20-mm2.orig/include/linux/freezer.h > > +++ linux-2.6.20-mm2/include/linux/freezer.h > > @@ -58,17 +58,13 @@ static inline void frozen_process(struct > > clear_tsk_thread_flag(p, TIF_FREEZE); > > } > > > > -extern void refrigerator(void); > > +extern int refrigerator(void); > > extern int freeze_processes(void); > > extern void thaw_processes(void); > > > > static inline int try_to_freeze(void) > > { > > - if (freezing(current)) { > > - refrigerator(); > > - return 1; > > - } else > > - return 0; > > + return refrigerator(); > > } > > > > /* > > @@ -104,7 +100,7 @@ static inline void freeze(struct task_st > > static inline int thaw_process(struct task_struct *p) { return 1; } > > static inline void frozen_process(struct task_struct *p) { BUG(); } > > > > -static inline void refrigerator(void) {} > > +static inline int refrigerator(void) { return 0; } > > static inline int freeze_processes(void) { BUG(); return 0; } > > static inline void thaw_processes(void) {} > > > > Index: linux-2.6.20-mm2/kernel/power/process.c > > =================================================================== > > --- linux-2.6.20-mm2.orig/kernel/power/process.c > > +++ linux-2.6.20-mm2/kernel/power/process.c > > @@ -24,6 +24,8 @@ > > #define FREEZER_KERNEL_THREADS 0 > > #define FREEZER_USER_SPACE 1 > > > > +spinlock_t refrigerator_lock; > > + > > static inline int freezeable(struct task_struct * p) > > { > > if ((p == current) || > > @@ -34,15 +36,23 @@ static inline int freezeable(struct task > > } > > > > /* Refrigerator is place where frozen processes are stored :-). */ > > -void refrigerator(void) > > +int refrigerator(void) > > { > > /* Hmm, should we be allowed to suspend when there are realtime > > processes around? */ > > long save; > > + > > + spin_lock(&refrigerator_lock); > > I hope we can do this without a global lock that is acquired on each > try_to_freeze() call! Yes. Here's the current version (try_to_freeze() is unchanged, so the lock is only taken by the tasks that are going to freeze, or so they think): --- kernel/power/process.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) Index: linux-2.6.20-mm2/kernel/power/process.c =================================================================== --- linux-2.6.20-mm2.orig/kernel/power/process.c +++ linux-2.6.20-mm2/kernel/power/process.c @@ -24,6 +24,8 @@ #define FREEZER_KERNEL_THREADS 0 #define FREEZER_USER_SPACE 1 +static spinlock_t refrigerator_lock; + static inline int freezeable(struct task_struct * p) { if ((p == current) || @@ -39,10 +41,18 @@ void refrigerator(void) /* Hmm, should we be allowed to suspend when there are realtime processes around? */ long save; + + spin_lock(&refrigerator_lock); + if (freezing(current)) { + frozen_process(current); + spin_unlock(&refrigerator_lock); + } else { + spin_unlock(&refrigerator_lock); + return; + } save = current->state; pr_debug("%s entered refrigerator\n", current->comm); - frozen_process(current); spin_lock_irq(¤t->sighand->siglock); recalc_sigpending(); /* We sent fake signal, clean it up */ spin_unlock_irq(¤t->sighand->siglock); @@ -143,6 +153,7 @@ static unsigned int try_to_freeze_tasks( "kernel threads", TIMEOUT / HZ, todo); read_lock(&tasklist_lock); + spin_lock(&refrigerator_lock); do_each_thread(g, p) { if (is_user_space(p) == !freeze_user_space) continue; @@ -152,6 +163,7 @@ static unsigned int try_to_freeze_tasks( cancel_freezing(p); } while_each_thread(g, p); + spin_unlock(&refrigerator_lock); read_unlock(&tasklist_lock); } @@ -169,6 +181,7 @@ int freeze_processes(void) unsigned int nr_unfrozen; printk("Stopping tasks ... "); + spin_lock_init(&refrigerator_lock); nr_unfrozen = try_to_freeze_tasks(FREEZER_USER_SPACE); if (nr_unfrozen) return nr_unfrozen; - 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/