Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751219AbXBVRKt (ORCPT ); Thu, 22 Feb 2007 12:10:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751213AbXBVRKt (ORCPT ); Thu, 22 Feb 2007 12:10:49 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:44993 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751240AbXBVRKs (ORCPT ); Thu, 22 Feb 2007 12:10:48 -0500 From: "Rafael J. Wysocki" To: Oleg Nesterov Subject: Re: freezer problems Date: Thu, 22 Feb 2007 18:03:37 +0100 User-Agent: KMail/1.9.5 Cc: paulmck@linux.vnet.ibm.com, 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> <200702220010.54126.rjw@sisk.pl> <20070222104747.GA505@tv-sign.ru> In-Reply-To: <20070222104747.GA505@tv-sign.ru> MIME-Version: 1.0 Content-Type: Multipart/Mixed; boundary="Boundary-00=_tzc3Fksr1nxJ2E+" Message-Id: <200702221803.41549.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9384 Lines: 290 --Boundary-00=_tzc3Fksr1nxJ2E+ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline On Thursday, 22 February 2007 11:47, Oleg Nesterov wrote: > On 02/22, Rafael J. Wysocki wrote: > > > > Okay, below is what I have right now (compilation tested on x86_64): > > > > This patch fixes the vfork problem by adding the PF_FREEZER_SKIP flag that > > can be used by tasks to tell the freezer not to count them as freezeable and > > making the vfork parents set this flag before they call wait_for_completion(). > > > > Secondly, it fixes the race which happens it a task with TIF_FREEZE set is > > preempted right before calling frozen_process() in refrigerator() and stays > > unforzen until after thaw_tasks() runs and checks its status. For this purpose > > task_lock() is used. > > Great! But please be kind to those of us who read the source control history > trying to understand the code. Could you make 2 separate patches? Okay, attached. The first one closes the race between thaw_tasks() and the refrigerator that can occurs if the freezing fails. The second one fixes the vfork problem (should go on top of the first one). > > @@ -207,7 +209,7 @@ static void thaw_tasks(int thaw_user_spa > > if (is_user_space(p) == !thaw_user_space) > > continue; > > > > - if (!thaw_process(p)) > > + if (!thaw_process(p) && !freezer_should_skip(p)) > > printk(KERN_WARNING " Strange, %s not stopped\n", > > This is racy, the warning could be false. We wake up the task, testing > its ->flags is not reliable. > > Damn. PF_FREEZER_SKIP task could be woken before, clear PF_FREEZER_SKIP, > but not frozen. > > We can change freezer_count() to clear PF_FREEZER_SKIP after try_to_freeze(), > not before. Now thaw_process() can take PF_FREEZER_SKIP into account and > return "true". > > But this means the task may be PF_FREEZER_SKIP | PF_FROZEN. What if we we > call try_to_freeze_tasks() soon after thaw_tasks()? We may hit the task which > leaves the refrigerator, but didn't clear PF_FREEZER_SKIP yet. This means > that thaw_process() should clear PF_FREEZER_SKIP as well. This is messy :( > > Any other ideas? In any case we should imho avoid a separate loop for > PF_FREEZER_SKIP tasks to just fix debug messages. In fact it can't help > anyway. Why don't we just drop the warning? try_to_freeze_tasks() should give us a warning if there's anything wrong anyway. Greetings, Rafael --Boundary-00=_tzc3Fksr1nxJ2E+ Content-Type: text/x-diff; charset="iso-8859-1"; name="freezer-fix-theoretical-race.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="freezer-fix-theoretical-race.patch" include/linux/freezer.h | 4 ++++ kernel/power/process.c | 14 +++++++++++++- 2 files changed, 17 insertions(+), 1 deletion(-) 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 @@ -40,11 +40,15 @@ static inline void do_not_freeze(struct */ static inline int thaw_process(struct task_struct *p) { + task_lock(p); if (frozen(p)) { p->flags &= ~PF_FROZEN; + task_unlock(p); wake_up_process(p); return 1; } + clear_tsk_thread_flag(p, TIF_FREEZE); + task_unlock(p); return 0; } 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 @@ -39,10 +39,18 @@ void refrigerator(void) /* Hmm, should we be allowed to suspend when there are realtime processes around? */ long save; + + task_lock(current); + if (freezing(current)) { + frozen_process(current); + task_unlock(current); + } else { + task_unlock(current); + 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); @@ -79,12 +87,16 @@ static void cancel_freezing(struct task_ { unsigned long flags; + task_lock(p); if (freezing(p)) { pr_debug(" clean up: %s\n", p->comm); do_not_freeze(p); + task_unlock(p); spin_lock_irqsave(&p->sighand->siglock, flags); recalc_sigpending_tsk(p); spin_unlock_irqrestore(&p->sighand->siglock, flags); + } else { + task_unlock(p); } } --Boundary-00=_tzc3Fksr1nxJ2E+ Content-Type: text/x-diff; charset="iso-8859-1"; name="freezer-fix-vfork-problem.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="freezer-fix-vfork-problem.patch" include/linux/freezer.h | 30 ++++++++++++++++++++++++++++-- include/linux/sched.h | 1 + kernel/fork.c | 3 +++ kernel/power/process.c | 29 +++++++++-------------------- 4 files changed, 41 insertions(+), 22 deletions(-) Index: linux-2.6.20-mm2/include/linux/sched.h =================================================================== --- linux-2.6.20-mm2.orig/include/linux/sched.h +++ linux-2.6.20-mm2/include/linux/sched.h @@ -1189,6 +1189,7 @@ static inline void put_task_struct(struc #define PF_SPREAD_SLAB 0x02000000 /* Spread some slab caches over cpuset */ #define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */ #define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */ +#define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezeable */ /* * Only the _current_ task can read/write to tsk->flags, but other 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 @@ -75,7 +75,31 @@ static inline int try_to_freeze(void) return 0; } -extern void thaw_some_processes(int all); +/* + * Tell the freezer not to count current task as freezeable + */ +static inline void freezer_do_not_count(void) +{ + current->flags |= PF_FREEZER_SKIP; +} + +/* + * Try to freeze the current task and tell the freezer to count it as freezeable + * again + */ +static inline void freezer_count(void) +{ + current->flags &= ~PF_FREEZER_SKIP; + try_to_freeze(); +} + +/* + * Check if the task should be counted as freezeable by the freezer + */ +static inline int freezer_should_skip(struct task_struct *p) +{ + return !!(p->flags & PF_FREEZER_SKIP); +} #else static inline int frozen(struct task_struct *p) { return 0; } @@ -90,5 +114,7 @@ static inline void thaw_processes(void) static inline int try_to_freeze(void) { return 0; } - +static inline void freezer_do_not_count(void) {} +static inline void freezer_count(void) {} +static inline int freezer_should_skip(struct task_struct *p) { return 0; } #endif Index: linux-2.6.20-mm2/kernel/fork.c =================================================================== --- linux-2.6.20-mm2.orig/kernel/fork.c +++ linux-2.6.20-mm2/kernel/fork.c @@ -50,6 +50,7 @@ #include #include #include +#include #include #include @@ -1393,7 +1394,9 @@ long do_fork(unsigned long clone_flags, tracehook_report_clone_complete(clone_flags, nr, p); if (clone_flags & CLONE_VFORK) { + freezer_do_not_count(); wait_for_completion(&vfork); + freezer_count(); tracehook_report_vfork_done(p, nr); } } else { 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 @@ -131,22 +131,12 @@ static unsigned int try_to_freeze_tasks( cancel_freezing(p); continue; } - if (is_user_space(p)) { - if (!freeze_user_space) - continue; - - /* Freeze the task unless there is a vfork - * completion pending - */ - if (!p->vfork_done) - freeze_process(p); - } else { - if (freeze_user_space) - continue; + if (is_user_space(p) == !freeze_user_space) + continue; - freeze_process(p); - } - todo++; + freeze_process(p); + if (!freezer_should_skip(p)) + todo++; } while_each_thread(g, p); read_unlock(&tasklist_lock); yield(); /* Yield is okay here */ @@ -171,8 +161,9 @@ static unsigned int try_to_freeze_tasks( if (is_user_space(p) == !freeze_user_space) continue; - if (freezeable(p) && !frozen(p)) - printk(KERN_ERR " %s\n", p->comm); + if (freezeable(p) && !frozen(p) && + !freezer_should_skip(p)) + printk(KERN_WARNING " %s\n", p->comm); cancel_freezing(p); } while_each_thread(g, p); @@ -219,9 +210,7 @@ static void thaw_tasks(int thaw_user_spa if (is_user_space(p) == !thaw_user_space) continue; - if (!thaw_process(p)) - printk(KERN_WARNING " Strange, %s not stopped\n", - p->comm ); + thaw_process(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); } --Boundary-00=_tzc3Fksr1nxJ2E+-- - 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/