From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Oleg Nesterov <oleg@tv-sign.ru>,
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 <pavel@ucw.cz>
Subject: Re: freezer problems
Date: Wed, 21 Feb 2007 10:27:52 -0800 [thread overview]
Message-ID: <20070221182752.GE7063@linux.vnet.ibm.com> (raw)
In-Reply-To: <200702211913.41883.rjw@sisk.pl>
On Wed, Feb 21, 2007 at 07:13:40PM +0100, Rafael J. Wysocki wrote:
> 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):
Ah, OK, that should work much better from a lock-contention viewpoint!
Thanx, Paul
> ---
> 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;
next prev parent reply other threads:[~2007-02-21 18:27 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-14 14:40 [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug Gautham R Shenoy
2007-02-14 14:42 ` [RFC PATCH(Experimental) 1/4] freezer-cpu-hotplug core Gautham R Shenoy
2007-02-14 14:43 ` [RFC PATCH(Experimental) 2/4] Revert changes to workqueue.c Gautham R Shenoy
2007-02-14 14:43 ` [RFC PATCH(Experimental) 3/4] Revert changes to sched.c and slab.c Gautham R Shenoy
2007-02-14 14:44 ` [RFC PATCH(Experimental) 4/4] Rip out lock_cpu_hotplug from linux Gautham R Shenoy
2007-02-14 14:59 ` [RFC PATCH(Experimental) 2/4] Revert changes to workqueue.c Srivatsa Vaddagiri
2007-02-14 15:24 ` Srivatsa Vaddagiri
2007-02-14 20:23 ` Oleg Nesterov
2007-02-14 20:09 ` Oleg Nesterov
2007-02-16 5:26 ` Srivatsa Vaddagiri
2007-02-16 15:33 ` Oleg Nesterov
2007-02-16 16:47 ` Srivatsa Vaddagiri
2007-02-16 18:45 ` Oleg Nesterov
2007-02-16 23:59 ` Oleg Nesterov
2007-02-17 2:29 ` Srivatsa Vaddagiri
2007-02-17 21:59 ` Oleg Nesterov
2007-02-20 15:12 ` Srivatsa Vaddagiri
2007-02-20 20:09 ` Oleg Nesterov
2007-02-21 6:29 ` Srivatsa Vaddagiri
2007-02-21 14:30 ` Oleg Nesterov
2007-02-21 14:37 ` Gautham R Shenoy
2007-02-21 15:53 ` Srivatsa Vaddagiri
2007-02-14 15:31 ` [RFC PATCH(Experimental) 1/4] freezer-cpu-hotplug core Srivatsa Vaddagiri
2007-02-14 19:47 ` Oleg Nesterov
2007-02-16 6:48 ` Srivatsa Vaddagiri
2007-02-16 15:47 ` Oleg Nesterov
2007-02-14 20:22 ` Oleg Nesterov
2007-02-16 7:16 ` Srivatsa Vaddagiri
2007-02-16 8:12 ` Srivatsa Vaddagiri
2007-02-16 9:29 ` Rafael J. Wysocki
2007-02-16 9:59 ` Srivatsa Vaddagiri
2007-02-16 11:06 ` Rafael J. Wysocki
2007-02-16 19:46 ` Oleg Nesterov
2007-02-17 2:31 ` Srivatsa Vaddagiri
2007-02-17 5:32 ` Gautham R Shenoy
2007-02-17 11:19 ` Gautham R Shenoy
2007-02-16 16:06 ` Oleg Nesterov
2007-02-14 21:43 ` [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug Rafael J. Wysocki
2007-02-15 6:34 ` Gautham R Shenoy
2007-02-15 8:09 ` Rafael J. Wysocki
2007-02-15 12:20 ` Gautham R Shenoy
2007-02-15 13:31 ` Rafael J. Wysocki
2007-02-15 14:25 ` Gautham R Shenoy
2007-02-17 11:24 ` Rafael J. Wysocki
2007-02-17 21:34 ` Oleg Nesterov
2007-02-17 22:24 ` Rafael J. Wysocki
2007-02-17 23:42 ` Oleg Nesterov
2007-02-17 23:47 ` Oleg Nesterov
2007-02-18 10:43 ` Rafael J. Wysocki
2007-02-18 11:31 ` Oleg Nesterov
2007-02-18 12:14 ` Rafael J. Wysocki
2007-02-18 14:52 ` freezer problems Oleg Nesterov
2007-02-18 15:14 ` Rafael J. Wysocki
2007-02-18 16:19 ` Oleg Nesterov
2007-02-18 18:14 ` Rafael J. Wysocki
2007-02-18 18:56 ` Rafael J. Wysocki
2007-02-18 22:01 ` Oleg Nesterov
2007-02-18 23:19 ` Rafael J. Wysocki
2007-02-19 20:23 ` Oleg Nesterov
2007-02-19 21:21 ` Rafael J. Wysocki
2007-02-19 22:41 ` Oleg Nesterov
2007-02-19 23:35 ` Rafael J. Wysocki
2007-02-20 0:12 ` Oleg Nesterov
2007-02-20 0:32 ` Rafael J. Wysocki
2007-02-20 0:50 ` Oleg Nesterov
2007-02-20 18:28 ` Rafael J. Wysocki
2007-02-20 18:29 ` Rafael J. Wysocki
2007-02-21 18:14 ` Paul E. McKenney
2007-02-21 18:13 ` Rafael J. Wysocki
2007-02-21 18:27 ` Paul E. McKenney [this message]
2007-02-21 20:03 ` Oleg Nesterov
2007-02-21 20:47 ` Rafael J. Wysocki
2007-02-21 21:06 ` Paul E. McKenney
2007-02-21 23:10 ` Rafael J. Wysocki
2007-02-22 10:47 ` Oleg Nesterov
2007-02-22 11:33 ` Oleg Nesterov
2007-02-22 17:03 ` Rafael J. Wysocki
2007-02-22 17:44 ` Oleg Nesterov
2007-02-22 21:56 ` Rafael J. Wysocki
2007-02-23 18:15 ` Oleg Nesterov
2007-02-23 3:02 ` Gautham R Shenoy
2007-02-18 15:09 ` [RFC PATCH(Experimental) 0/4] Freezer based Cpu-hotplug Rafael J. Wysocki
2007-02-18 16:11 ` Oleg Nesterov
2007-02-18 18:51 ` Rafael J. Wysocki
2007-02-18 10:32 ` Rafael J. Wysocki
2007-02-18 11:32 ` Oleg Nesterov
2007-02-18 12:12 ` Rafael J. Wysocki
2007-02-18 15:06 ` Oleg Nesterov
2007-02-18 12:56 ` Pavel Machek
2007-02-21 14:52 ` Gautham R Shenoy
2007-02-21 19:42 ` Pavel Machek
[not found] ` <200702231041.17136.rjw@sisk.pl>
[not found] ` <20070223100817.GA10973@in.ibm.com>
[not found] ` <200702231115.00718.rjw@sisk.pl>
[not found] ` <20070223104723.GB10973@in.ibm.com>
[not found] ` <20070223110201.GC10973@in.ibm.com>
2007-02-23 19:03 ` freezer problems Gautham R Shenoy
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