Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751970AbXBVWD1 (ORCPT ); Thu, 22 Feb 2007 17:03:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751976AbXBVWD1 (ORCPT ); Thu, 22 Feb 2007 17:03:27 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:45978 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751970AbXBVWD0 (ORCPT ); Thu, 22 Feb 2007 17:03:26 -0500 From: "Rafael J. Wysocki" To: Oleg Nesterov Subject: Re: freezer problems Date: Thu, 22 Feb 2007 22:56:18 +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> <200702221803.41549.rjw@sisk.pl> <20070222174439.GA236@tv-sign.ru> In-Reply-To: <20070222174439.GA236@tv-sign.ru> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200702222256.19582.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6388 Lines: 198 On Thursday, 22 February 2007 18:44, Oleg Nesterov wrote: > On 02/22, Rafael J. Wysocki wrote: > > > > 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). > > Looks good to me. > > > > 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. > > Indeed :) Still, there is a tiny race in the error path of try_to_freeze_tasks(), where a vfork parent process can be preempted after clearing PF_FREEZER_SKIP and before entering refrigerator(), so try_to_freeze_tasks() will mistakenly report that this process has caused a problem. I think this race can be closed by (1) clearing PF_FREEZER_SKIP after calling try_to_freeze() in freezer_count(), (2) clearing PF_FREEZER_SKIP in refrigerator() before calling frozen_process() and (3) taking task_lock() around the warning check in the error path of try_to_freeze_tasks(). I have modified freezer-fix-vfork-problem.patch to implement this (appended; it assumes that freezer-fix-theoretical-race.patch has already been applied). If this is the right thing to do, I think there's a reason to additionally move task_lock/unlock() from cancel_freezing() to the error path in try_to_freeze_tasks(). Greetings, Rafael include/linux/freezer.h | 30 ++++++++++++++++++++++++++++-- include/linux/sched.h | 1 + kernel/fork.c | 3 +++ kernel/power/process.c | 32 +++++++++++++------------------- 4 files changed, 45 insertions(+), 21 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) +{ + try_to_freeze(); + current->flags &= ~PF_FREEZER_SKIP; +} + +/* + * 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 @@ -42,6 +42,7 @@ void refrigerator(void) task_lock(current); if (freezing(current)) { + current->flags &= ~PF_FREEZER_SKIP; frozen_process(current); task_unlock(current); } else { @@ -131,22 +132,12 @@ 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 */ @@ -171,9 +162,14 @@ static unsigned int try_to_freeze_tasks( if (is_user_space(p) == !freeze_user_space) continue; - if (freezeable(p) && !frozen(p)) + task_lock(p); + + if (freezeable(p) && !frozen(p) && + !freezer_should_skip(p)) printk(KERN_ERR " %s\n", p->comm); + task_unlock(p); + cancel_freezing(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); @@ -219,9 +215,7 @@ 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); } - 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/