Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1422701AbXBUSON (ORCPT ); Wed, 21 Feb 2007 13:14:13 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422756AbXBUSON (ORCPT ); Wed, 21 Feb 2007 13:14:13 -0500 Received: from e33.co.us.ibm.com ([32.97.110.151]:52796 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422701AbXBUSOK (ORCPT ); Wed, 21 Feb 2007 13:14:10 -0500 Date: Wed, 21 Feb 2007 10:14:04 -0800 From: "Paul E. McKenney" To: "Rafael J. Wysocki" 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 Subject: Re: freezer problems Message-ID: <20070221181404.GC7063@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20070214144031.GA15257@in.ibm.com> <20070220001209.GA15991@tv-sign.ru> <200702200132.12847.rjw@sisk.pl> <200702201929.03776.rjw@sisk.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200702201929.03776.rjw@sisk.pl> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4958 Lines: 144 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! > + if (freezing(current)) { Would it be possible to acquire the lock here instead, then recheck here? Or use a per-thread lock? (Yes, this would make the error checking path have to acquire a very large number of threads, but... Thanx, Paul > + frozen_process(current); > + spin_unlock(&refrigerator_lock); > + } else { > + spin_unlock(&refrigerator_lock); > + return 0; > + } > 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); > @@ -53,6 +63,7 @@ void refrigerator(void) > } > pr_debug("%s left refrigerator\n", current->comm); > current->state = save; > + return 1; > } > > static inline void freeze_process(struct task_struct *p) > @@ -143,6 +154,7 @@ 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 +164,7 @@ 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 +182,7 @@ 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/