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2024-08-17sched,freezer: Mark TASK_FROZEN specialPeter Zijlstra
The special task states are those that do not suffer spurious wakeups, TASK_FROZEN is very much one of those, mark it as such. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <vschneid@redhat.com> Tested-by: Valentin Schneider <vschneid@redhat.com> Link: https://lkml.kernel.org/r/20240727105029.998329901@infradead.org
2023-12-23Merge tag 'v6.7-rc6' into sched/core, to pick up fixesIngo Molnar
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2023-11-29freezer,sched: Clean saved_state when restoring it during thawElliot Berman
Clean saved_state after using it during thaw. Cleaning the saved_state allows us to avoid some unnecessary branches in ttwu_state_match. Signed-off-by: Elliot Berman <quic_eberman@quicinc.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20231120-freezer-state-multiple-thaws-v1-2-f2e1dd7ce5a2@quicinc.com
2023-11-29freezer,sched: Do not restore saved_state of a thawed taskElliot Berman
It is possible for a task to be thawed multiple times when mixing the *legacy* cgroup freezer and system-wide freezer. To do this, freeze the cgroup, do system-wide freeze/thaw, then thaw the cgroup. When this happens, then a stale saved_state can be written to the task's state and cause task to hang indefinitely. Fix this by only trying to thaw tasks that are actually frozen. This change also has the marginal benefit avoiding unnecessary wake_up_state(p, TASK_FROZEN) if we know the task is already thawed. There is not possibility of time-of-compare/time-of-use race when we skip the wake_up_state because entering/exiting TASK_FROZEN is guarded by freezer_lock. Fixes: 8f0eed4a78a8 ("freezer,sched: Use saved_state to reduce some spurious wakeups") Signed-off-by: Elliot Berman <quic_eberman@quicinc.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Abhijeet Dharmapurikar <quic_adharmap@quicinc.com> Link: https://lore.kernel.org/r/20231120-freezer-state-multiple-thaws-v1-1-f2e1dd7ce5a2@quicinc.com
2023-09-18freezer,sched: Use saved_state to reduce some spurious wakeupsElliot Berman
After commit f5d39b020809 ("freezer,sched: Rewrite core freezer logic"), tasks that transition directly from TASK_FREEZABLE to TASK_FROZEN are always woken up on the thaw path. Prior to that commit, tasks could ask freezer to consider them "frozen enough" via freezer_do_not_count(). The commit replaced freezer_do_not_count() with a TASK_FREEZABLE state which allows freezer to immediately mark the task as TASK_FROZEN without waking up the task. This is efficient for the suspend path, but on the thaw path, the task is always woken up even if the task didn't need to wake up and goes back to its TASK_(UN)INTERRUPTIBLE state. Although these tasks are capable of handling of the wakeup, we can observe a power/perf impact from the extra wakeup. We observed on Android many tasks wait in the TASK_FREEZABLE state (particularly due to many of them being binder clients). We observed nearly 4x the number of tasks and a corresponding linear increase in latency and power consumption when thawing the system. The latency increased from ~15ms to ~50ms. Avoid the spurious wakeups by saving the state of TASK_FREEZABLE tasks. If the task was running before entering TASK_FROZEN state (__refrigerator()) or if the task received a wake up for the saved state, then the task is woken on thaw. saved_state from PREEMPT_RT locks can be re-used because freezer would not stomp on the rtlock wait flow: TASK_RTLOCK_WAIT isn't considered freezable. Reported-by: Prakash Viswalingam <quic_prakashv@quicinc.com> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
2022-09-07freezer,sched: Rewrite core freezer logicPeter Zijlstra
Rewrite the core freezer to behave better wrt thawing and be simpler in general. By replacing PF_FROZEN with TASK_FROZEN, a special block state, it is ensured frozen tasks stay frozen until thawed and don't randomly wake up early, as is currently possible. As such, it does away with PF_FROZEN and PF_FREEZER_SKIP, freeing up two PF_flags (yay!). Specifically; the current scheme works a little like: freezer_do_not_count(); schedule(); freezer_count(); And either the task is blocked, or it lands in try_to_freezer() through freezer_count(). Now, when it is blocked, the freezer considers it frozen and continues. However, on thawing, once pm_freezing is cleared, freezer_count() stops working, and any random/spurious wakeup will let a task run before its time. That is, thawing tries to thaw things in explicit order; kernel threads and workqueues before doing bringing SMP back before userspace etc.. However due to the above mentioned races it is entirely possible for userspace tasks to thaw (by accident) before SMP is back. This can be a fatal problem in asymmetric ISA architectures (eg ARMv9) where the userspace task requires a special CPU to run. As said; replace this with a special task state TASK_FROZEN and add the following state transitions: TASK_FREEZABLE -> TASK_FROZEN __TASK_STOPPED -> TASK_FROZEN __TASK_TRACED -> TASK_FROZEN The new TASK_FREEZABLE can be set on any state part of TASK_NORMAL (IOW. TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE) -- any such state is already required to deal with spurious wakeups and the freezer causes one such when thawing the task (since the original state is lost). The special __TASK_{STOPPED,TRACED} states *can* be restored since their canonical state is in ->jobctl. With this, frozen tasks need an explicit TASK_FROZEN wakeup and are free of undue (early / spurious) wakeups. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Ingo Molnar <mingo@kernel.org> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Link: https://lore.kernel.org/r/20220822114649.055452969@infradead.org
2021-06-18sched: Add get_current_state()Peter Zijlstra
Remove yet another few p->state accesses. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20210611082838.347475156@infradead.org
2021-03-27Revert "kernel: freezer should treat PF_IO_WORKER like PF_KTHREAD for freezing"Jens Axboe
This reverts commit 15b2219facadec583c24523eed40fa45865f859f. Before IO threads accepted signals, the freezer using take signals to wake up an IO thread would cause them to loop without any way to clear the pending signal. That is no longer the case, so stop special casing PF_IO_WORKER in the freezer. Signed-off-by: Jens Axboe <axboe@kernel.dk>
2021-03-12kernel: freezer should treat PF_IO_WORKER like PF_KTHREAD for freezingJens Axboe
Don't send fake signals to PF_IO_WORKER threads, they don't accept signals. Just treat them like kthreads in this regard, all they need is a wakeup as no forced kernel/user transition is needed. Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-10-06Revert "libata, freezer: avoid block device removal while system is frozen"Mika Westerberg
This reverts commit 85fbd722ad0f5d64d1ad15888cd1eb2188bfb557. The commit was added as a quick band-aid for a hang that happened when a block device was removed during system suspend. Now that bdi_wq is not freezable anymore the hang should not be possible and we can get rid of this hack by reverting it. Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-05-21treewide: Add SPDX license identifier for missed filesThomas Gleixner
Add SPDX license identifiers to all files which: - Have no license information of any form - Have EXPORT_.*_SYMBOL_GPL inside which was used in the initial scan/conversion to ignore the file These files fall under the project license, GPL v2 only. The resulting SPDX license identifier is: GPL-2.0-only Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2018-08-06PM / reboot: Eliminate race between reboot and suspendPingfan Liu
At present, "systemctl suspend" and "shutdown" can run in parrallel. A system can suspend after devices_shutdown(), and resume. Then the shutdown task goes on to power off. This causes many devices are not really shut off. Hence replacing reboot_mutex with system_transition_mutex (renamed from pm_mutex) to achieve the exclusion. The renaming of pm_mutex as system_transition_mutex can be better to reflect the purpose of the mutex. Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Acked-by: Pavel Machek <pavel@ucw.cz> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2016-07-28freezer, oom: check TIF_MEMDIE on the correct taskMichal Hocko
freezing_slow_path() is checking TIF_MEMDIE to skip OOM killed tasks. It is, however, checking the flag on the current task rather than the given one. This is really confusing because freezing() can be called also on !current tasks. It would end up working correctly for its main purpose because __refrigerator will be always called on the current task so the oom victim will never get frozen. But it could lead to surprising results when a task which is freezing a cgroup got oom killed because only part of the cgroup would get frozen. This is highly unlikely but worth fixing as the resulting code would be more clear anyway. Link: http://lkml.kernel.org/r/1467029719-17602-2-git-send-email-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Cc: David Rientjes <rientjes@google.com> Cc: Miao Xie <miaox@cn.fujitsu.com> Cc: Miao Xie <miaoxie@huawei.com> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-10-21freezer: remove obsolete comments in __thaw_task()Cong Wang
__thaw_task() no longer clears frozen flag since commit a3201227f803 (freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE). Reviewed-by: Michal Hocko <mhocko@suse.cz> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-10-21freezer: Do not freeze tasks killed by OOM killerCong Wang
Since f660daac474c6f (oom: thaw threads if oom killed thread is frozen before deferring) OOM killer relies on being able to thaw a frozen task to handle OOM situation but a3201227f803 (freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE) has reorganized the code and stopped clearing freeze flag in __thaw_task. This means that the target task only wakes up and goes into the fridge again because the freezing condition hasn't changed for it. This reintroduces the bug fixed by f660daac474c6f. Fix the issue by checking for TIF_MEMDIE thread flag in freezing_slow_path and exclude the task from freezing completely. If a task was already frozen it would get woken by __thaw_task from OOM killer and get out of freezer after rechecking freezing(). Changes since v1 - put TIF_MEMDIE check into freezing_slowpath rather than in __refrigerator as per Oleg - return __thaw_task into oom_scan_process_thread because oom_kill_process will not wake task in the fridge because it is sleeping uninterruptible [mhocko@suse.cz: rewrote the changelog] Fixes: a3201227f803 (freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE) Cc: 3.3+ <stable@vger.kernel.org> # 3.3+ Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: Michal Hocko <mhocko@suse.cz> Acked-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2013-12-19libata, freezer: avoid block device removal while system is frozenTejun Heo
Freezable kthreads and workqueues are fundamentally problematic in that they effectively introduce a big kernel lock widely used in the kernel and have already been the culprit of several deadlock scenarios. This is the latest occurrence. During resume, libata rescans all the ports and revalidates all pre-existing devices. If it determines that a device has gone missing, the device is removed from the system which involves invalidating block device and flushing bdi while holding driver core layer locks. Unfortunately, this can race with the rest of device resume. Because freezable kthreads and workqueues are thawed after device resume is complete and block device removal depends on freezable workqueues and kthreads (e.g. bdi_wq, jbd2) to make progress, this can lead to deadlock - block device removal can't proceed because kthreads are frozen and kthreads can't be thawed because device resume is blocked behind block device removal. 839a8e8660b6 ("writeback: replace custom worker pool implementation with unbound workqueue") made this particular deadlock scenario more visible but the underlying problem has always been there - the original forker task and jbd2 are freezable too. In fact, this is highly likely just one of many possible deadlock scenarios given that freezer behaves as a big kernel lock and we don't have any debug mechanism around it. I believe the right thing to do is getting rid of freezable kthreads and workqueues. This is something fundamentally broken. For now, implement a funny workaround in libata - just avoid doing block device hot[un]plug while the system is frozen. Kernel engineering at its finest. :( v2: Add EXPORT_SYMBOL_GPL(pm_freezing) for cases where libata is built as a module. v3: Comment updated and polling interval changed to 10ms as suggested by Rafael. v4: Add #ifdef CONFIG_FREEZER around the hack as pm_freezing is not defined when FREEZER is not configured thus breaking build. Reported by kbuild test robot. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Tomaž Šolc <tomaz.solc@tablix.org> Reviewed-by: "Rafael J. Wysocki" <rjw@rjwysocki.net> Link: https://bugzilla.kernel.org/show_bug.cgi?id=62801 Link: http://lkml.kernel.org/r/20131213174932.GA27070@htj.dyndns.org Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Len Brown <len.brown@intel.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: stable@vger.kernel.org Cc: kbuild test robot <fengguang.wu@intel.com>
2013-07-30freezer: set PF_SUSPEND_TASK flag on tasks that call freeze_processesColin Cross
Calling freeze_processes sets a global flag that will cause any process that calls try_to_freeze to enter the refrigerator. It skips sending a signal to the current task, but if the current task ever hits try_to_freeze, all threads will be frozen and the system will deadlock. Set a new flag, PF_SUSPEND_TASK, on the task that calls freeze_processes. The flag notifies the freezer that the thread is involved in suspend and should not be frozen. Also add a WARN_ON in thaw_processes if the caller does not have the PF_SUSPEND_TASK flag set to catch if a different task calls thaw_processes than the one that called freeze_processes, leaving a task with PF_SUSPEND_TASK permanently set on it. Threads that spawn off a task with PF_SUSPEND_TASK set (which swsusp does) will also have PF_SUSPEND_TASK set, preventing them from freezing while they are helping with suspend, but they need to be dead by the time suspend is triggered, otherwise they may run when userspace is expected to be frozen. Add a WARN_ON in thaw_processes if more than one thread has the PF_SUSPEND_TASK flag set. Reported-and-tested-by: Michael Leun <lkml20130126@newton.leun.net> Signed-off-by: Colin Cross <ccross@android.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2013-05-12freezer: skip waking up tasks with PF_FREEZER_SKIP setColin Cross
Android goes through suspend/resume very often (every few seconds when on a busy wifi network with the screen off), and a significant portion of the energy used to go in and out of suspend is spent in the freezer. If a task has called freezer_do_not_count(), don't bother waking it up. If it happens to wake up later it will call freezer_count() and immediately enter the refrigerator. Combined with patches to convert freezable helpers to use freezer_do_not_count() and convert common sites where idle userspace tasks are blocked to use the freezable helpers, this reduces the time and energy required to suspend and resume. Acked-by: Tejun Heo <tj@kernel.org> Acked-by: Pavel Machek <pavel@ucw.cz> Signed-off-by: Colin Cross <ccross@android.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2012-10-26freezer: change ptrace_stop/do_signal_stop to use freezable_schedule()Oleg Nesterov
try_to_freeze_tasks() and cgroup_freezer rely on scheduler locks to ensure that a task doing STOPPED/TRACED -> RUNNING transition can't escape freezing. This mostly works, but ptrace_stop() does not necessarily call schedule(), it can change task->state back to RUNNING and check freezing() without any lock/barrier in between. We could add the necessary barrier, but this patch changes ptrace_stop() and do_signal_stop() to use freezable_schedule(). This fixes the race, freezer_count() and freezer_should_skip() carefully avoid the race. And this simplifies the code, try_to_freeze_tasks/update_if_frozen no longer need to use task_is_stopped_or_traced() checks with the non trivial assumptions. We can rely on the mechanism which was specially designed to mark the sleeping task as "frozen enough". v2: As Tejun pointed out, we can also change get_signal_to_deliver() and move try_to_freeze() up before 'relock' label. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Tejun Heo <tj@kernel.org>
2012-03-04PM / Freezer: Remove references to TIF_FREEZE in commentsMarcos Paulo de Souza
This patch removes all the references in the code about the TIF_FREEZE flag removed by commit a3201227f803ad7fd43180c5195dbe5a2bf998aa freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE There still are some references to TIF_FREEZE in Documentation/power/freezing-of-tasks.txt, but it looks like that documentation needs more thorough work to reflect how the new freezer works, and hence merely removing the references to TIF_FREEZE won't really help. So I have not touched that part in this patch. Suggested-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Signed-off-by: Marcos Paulo de Souza <marcos.mage@gmail.com> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
2011-11-23freezer: kill unused set_freezable_with_signal()Tejun Heo
There's no in-kernel user of set_freezable_with_signal() left. Mixing TIF_SIGPENDING with kernel threads can lead to nasty corner cases as kernel threads never travel signal delivery path on their own. e.g. the current implementation is buggy in the cancelation path of __thaw_task(). It calls recalc_sigpending_and_wake() in an attempt to clear TIF_SIGPENDING but the function never clears it regardless of sigpending state. This means that signallable freezable kthreads may continue executing with !freezing() && stuck TIF_SIGPENDING, which can be troublesome. This patch removes set_freezable_with_signal() along with PF_FREEZER_NOSIG and recalc_sigpending*() calls in freezer. User tasks get TIF_SIGPENDING, kernel tasks get woken up and the spurious sigpending is dealt with in the usual signal delivery path. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Oleg Nesterov <oleg@redhat.com>
2011-11-21freezer: remove unused @sig_only from freeze_task()Tejun Heo
After "freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE", freezing() returns authoritative answer on whether the current task should freeze or not and freeze_task() doesn't need or use @sig_only. Remove it. While at it, rewrite function comment for freeze_task() and rename @sig_only to @user_only in try_to_freeze_tasks(). This patch doesn't cause any functional change. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Oleg Nesterov <oleg@redhat.com>
2011-11-21freezer: use lock_task_sighand() in fake_signal_wake_up()Tejun Heo
cgroup_freezer calls freeze_task() without holding tasklist_lock and, if the task is exiting, its ->sighand may be gone by the time fake_signal_wake_up() is called. Use lock_task_sighand() instead of accessing ->sighand directly. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Cc: "Rafael J. Wysocki" <rjw@sisk.pl> Cc: Paul Menage <paul@paulmenage.org>
2011-11-21freezer: restructure __refrigerator()Tejun Heo
If another freeze happens before all tasks leave FROZEN state after being thawed, the freezer can see the existing FROZEN and consider the tasks to be frozen but they can clear FROZEN without checking the new freezing(). Oleg suggested restructuring __refrigerator() such that there's single condition check section inside freezer_lock and sigpending is cleared afterwards, which fixes the problem and simplifies the code. Restructure accordingly. -v2: Frozen loop exited without releasing freezer_lock. Fixed. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
2011-11-21freezer: fix set_freezable[_with_signal]() raceTejun Heo
A kthread doing set_freezable*() may race with on-going PM freeze and the freezer might think all tasks are frozen while the new freezable kthread is merrily proceeding to execute code paths which aren't supposed to be executing during PM freeze. Reimplement set_freezable[_with_signal]() using __set_freezable() such that freezable PF flags are modified under freezer_lock and try_to_freeze() is called afterwards. This eliminates race condition against freezing. Note: Separated out from larger patch to resolve fix order dependency Oleg pointed out. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com>
2011-11-21freezer: remove should_send_signal() and update frozen()Tejun Heo
should_send_signal() is only used in freezer.c. Exporting them only increases chance of abuse. Open code the two users and remove it. Update frozen() to return bool. Signed-off-by: Tejun Heo <tj@kernel.org>
2011-11-21freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZETejun Heo
Using TIF_FREEZE for freezing worked when there was only single freezing condition (the PM one); however, now there is also the cgroup_freezer and single bit flag is getting clumsy. thaw_processes() is already testing whether cgroup freezing in in effect to avoid thawing tasks which were frozen by both PM and cgroup freezers. This is racy (nothing prevents race against cgroup freezing) and fragile. A much simpler way is to test actual freeze conditions from freezing() - ie. directly test whether PM or cgroup freezing is in effect. This patch adds variables to indicate whether and what type of freezing conditions are in effect and reimplements freezing() such that it directly tests whether any of the two freezing conditions is active and the task should freeze. On fast path, freezing() is still very cheap - it only tests system_freezing_cnt. This makes the clumsy dancing aroung TIF_FREEZE unnecessary and freeze/thaw operations more usual - updating state variables for the new state and nudging target tasks so that they notice the new state and comply. As long as the nudging happens after state update, it's race-free. * This allows use of freezing() in freeze_task(). Replace the open coded tests with freezing(). * p != current test is added to warning printing conditions in try_to_freeze_tasks() failure path. This is necessary as freezing() is now true for the task which initiated freezing too. -v2: Oleg pointed out that re-freezing FROZEN cgroup could increment system_freezing_cnt. Fixed. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Paul Menage <paul@paulmenage.org> (for the cgroup portions)
2011-11-21freezer: clean up freeze_processes() failure pathTejun Heo
freeze_processes() failure path is rather messy. Freezing is canceled for workqueues and tasks which aren't frozen yet but frozen tasks are left alone and should be thawed by the caller and of course some callers (xen and kexec) didn't do it. This patch updates __thaw_task() to handle cancelation correctly and makes freeze_processes() and freeze_kernel_threads() call thaw_processes() on failure instead so that the system is fully thawed on failure. Unnecessary [suspend_]thaw_processes() calls are removed from kernel/power/hibernate.c, suspend.c and user.c. While at it, restructure error checking if clause in suspend_prepare() to be less weird. -v2: Srivatsa spotted missing removal of suspend_thaw_processes() in suspend_prepare() and error in commit message. Updated. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
2011-11-21freezer: kill PF_FREEZINGTejun Heo
With the previous changes, there's no meaningful difference between PF_FREEZING and PF_FROZEN. Remove PF_FREEZING and use PF_FROZEN instead in task_contributes_to_load(). Signed-off-by: Tejun Heo <tj@kernel.org>
2011-11-21freezer: test freezable conditions while holding freezer_lockTejun Heo
try_to_freeze_tasks() and thaw_processes() use freezable() and frozen() as preliminary tests before initiating operations on a task. These are done without any synchronization and hinder with synchronization cleanup without any real performance benefits. In try_to_freeze_tasks(), open code self test and move PF_NOFREEZE and frozen() tests inside freezer_lock in freeze_task(). thaw_processes() can simply drop freezable() test as frozen() test in __thaw_task() is enough. Note: This used to be a part of larger patch to fix set_freezable() race. Separated out to satisfy ordering among dependent fixes. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com>
2011-11-21freezer: make freezing indicate freeze condition in effectTejun Heo
Currently freezing (TIF_FREEZE) and frozen (PF_FROZEN) states are interlocked - freezing is set to request freeze and when the task actually freezes, it clears freezing and sets frozen. This interlocking makes things more complex than necessary - freezing doesn't mean there's freezing condition in effect and frozen doesn't match the task actually entering and leaving frozen state (it's cleared by the thawing task). This patch makes freezing indicate that freeze condition is in effect. A task enters and stays frozen if freezing. This makes PF_FROZEN manipulation done only by the task itself and prevents wakeup from __thaw_task() leaking outside of refrigerator. The only place which needs to tell freezing && !frozen is try_to_freeze_task() to whine about tasks which don't enter frozen. It's updated to test the condition explicitly. With the change, frozen() state my linger after __thaw_task() until the task wakes up and exits fridge. This can trigger BUG_ON() in update_if_frozen(). Work it around by testing freezing() && frozen() instead of frozen(). -v2: Oleg pointed out missing re-check of freezing() when trying to clear FROZEN and possible spurious BUG_ON() trigger in update_if_frozen(). Both fixed. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul Menage <paul@paulmenage.org>
2011-11-21freezer: use dedicated lock instead of task_lock() + memory barrierTejun Heo
Freezer synchronization is needlessly complicated - it's by no means a hot path and the priority is staying unintrusive and safe. This patch makes it simply use a dedicated lock instead of piggy-backing on task_lock() and playing with memory barriers. On the failure path of try_to_freeze_tasks(), locking is moved from it to cancel_freezing(). This makes the frozen() test racy but the race here is a non-issue as the warning is printed for tasks which failed to enter frozen for 20 seconds and race on PF_FROZEN at the last moment doesn't change anything. This simplifies freezer implementation and eases further changes including some race fixes. Signed-off-by: Tejun Heo <tj@kernel.org>
2011-11-21freezer: rename thaw_process() to __thaw_task() and simplify the implementationTejun Heo
thaw_process() now has only internal users - system and cgroup freezers. Remove the unnecessary return value, rename, unexport and collapse __thaw_process() into it. This will help further updates to the freezer code. -v3: oom_kill grew a use of thaw_process() while this patch was pending. Convert it to use __thaw_task() for now. In the longer term, this should be handled by allowing tasks to die if killed even if it's frozen. -v2: minor style update as suggested by Matt. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Paul Menage <menage@google.com> Cc: Matt Helsley <matthltc@us.ibm.com>
2011-11-21freezer: implement and use kthread_freezable_should_stop()Tejun Heo
Writeback and thinkpad_acpi have been using thaw_process() to prevent deadlock between the freezer and kthread_stop(); unfortunately, this is inherently racy - nothing prevents freezing from happening between thaw_process() and kthread_stop(). This patch implements kthread_freezable_should_stop() which enters refrigerator if necessary but is guaranteed to return if kthread_stop() is invoked. Both thaw_process() users are converted to use the new function. Note that this deadlock condition exists for many of freezable kthreads. They need to be converted to use the new should_stop or freezable workqueue. Tested with synthetic test case. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Henrique de Moraes Holschuh <ibm-acpi@hmh.eng.br> Cc: Jens Axboe <axboe@kernel.dk> Cc: Oleg Nesterov <oleg@redhat.com>
2011-11-21freezer: unexport refrigerator() and update try_to_freeze() slightlyTejun Heo
There is no reason to export two functions for entering the refrigerator. Calling refrigerator() instead of try_to_freeze() doesn't save anything noticeable or removes any race condition. * Rename refrigerator() to __refrigerator() and make it return bool indicating whether it scheduled out for freezing. * Update try_to_freeze() to return bool and relay the return value of __refrigerator() if freezing(). * Convert all refrigerator() users to try_to_freeze(). * Update documentation accordingly. * While at it, add might_sleep() to try_to_freeze(). Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Samuel Ortiz <samuel@sortiz.org> Cc: Chris Mason <chris.mason@oracle.com> Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: Steven Whitehouse <swhiteho@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jan Kara <jack@suse.cz> Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp> Cc: Christoph Hellwig <hch@infradead.org>
2011-11-21freezer: fix current->state restoration race in refrigerator()Tejun Heo
refrigerator() saves current->state before entering frozen state and restores it before returning using __set_current_state(); however, this is racy, for example, please consider the following sequence. set_current_state(TASK_INTERRUPTIBLE); try_to_freeze(); if (kthread_should_stop()) break; schedule(); If kthread_stop() races with ->state restoration, the restoration can restore ->state to TASK_INTERRUPTIBLE after kthread_stop() sets it to TASK_RUNNING but kthread_should_stop() may still see zero ->should_stop because there's no memory barrier between restoring TASK_INTERRUPTIBLE and kthread_should_stop() test. This isn't restricted to kthread_should_stop(). current->state is often used in memory barrier based synchronization and silently restoring it w/o mb breaks them. Use set_current_state() instead. Signed-off-by: Tejun Heo <tj@kernel.org>
2011-11-06Merge branch 'modsplit-Oct31_2011' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux * 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux: (230 commits) Revert "tracing: Include module.h in define_trace.h" irq: don't put module.h into irq.h for tracking irqgen modules. bluetooth: macroize two small inlines to avoid module.h ip_vs.h: fix implicit use of module_get/module_put from module.h nf_conntrack.h: fix up fallout from implicit moduleparam.h presence include: replace linux/module.h with "struct module" wherever possible include: convert various register fcns to macros to avoid include chaining crypto.h: remove unused crypto_tfm_alg_modname() inline uwb.h: fix implicit use of asm/page.h for PAGE_SIZE pm_runtime.h: explicitly requires notifier.h linux/dmaengine.h: fix implicit use of bitmap.h and asm/page.h miscdevice.h: fix up implicit use of lists and types stop_machine.h: fix implicit use of smp.h for smp_processor_id of: fix implicit use of errno.h in include/linux/of.h of_platform.h: delete needless include <linux/module.h> acpi: remove module.h include from platform/aclinux.h miscdevice.h: delete unnecessary inclusion of module.h device_cgroup.h: delete needless include <linux/module.h> net: sch_generic remove redundant use of <linux/module.h> net: inet_timewait_sock doesnt need <linux/module.h> ... Fix up trivial conflicts (other header files, and removal of the ab3550 mfd driver) in - drivers/media/dvb/frontends/dibx000_common.c - drivers/media/video/{mt9m111.c,ov6650.c} - drivers/mfd/ab3550-core.c - include/linux/dmaengine.h
2011-11-04PM / Freezer: Revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() ↵Tejun Heo
wake TASK_KILLABLE tasks too" Commit 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK_KILLABLE tasks too" updated fake_signal_wake_up() used by freezer to wake up KILLABLE tasks. Sending unsolicited wakeups to tasks in killable sleep is dangerous as there are code paths which depend on tasks not waking up spuriously from KILLABLE sleep. For example. sys_read() or page can sleep in TASK_KILLABLE assuming that wait/down/whatever _killable can only fail if we can not return to the usermode. TASK_TRACED is another obvious example. The previous patch updated wait_event_freezekillable() such that it doesn't depend on the spurious wakeup. This patch reverts the offending commit. Note that the spurious KILLABLE wakeup had other implicit effects in KILLABLE sleeps in nfs and cifs and those will need further updates to regain freezekillable behavior. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
2011-10-31kernel: Map most files to use export.h instead of module.hPaul Gortmaker
The changed files were only including linux/module.h for the EXPORT_SYMBOL infrastructure, and nothing else. Revector them onto the isolated export header for faster compile times. Nothing to see here but a whole lot of instances of: -#include <linux/module.h> +#include <linux/export.h> This commit is only changing the kernel dir; next targets will probably be mm, fs, the arch dirs, etc. Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
2011-10-16PM / Freezer: Make fake_signal_wake_up() wake TASK_KILLABLE tasks tooJeff Layton
TASK_KILLABLE is often used to put tasks to sleep for quite some time. One of the most common uses is to put tasks to sleep while waiting for replies from a server on a networked filesystem (such as CIFS or NFS). Unfortunately, fake_signal_wake_up does not currently wake up tasks that are sleeping in TASK_KILLABLE state. This means that even if the code were in place to allow them to freeze while in this sleep, it wouldn't work anyway. This patch changes this function to wake tasks in this state as well. This should be harmless -- if the code doing the sleeping doesn't have handling to deal with freezer events, it should just go back to sleep. If it does, then this will allow that code to do the right thing. Signed-off-by: Jeff Layton <jlayton@redhat.com> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
2011-05-17Freezer: Use SMP barriersMike Frysinger
The freezer processes are dealing with multiple threads running simultaneously, and on a UP system, the memory reads/writes do not need barriers to keep things in sync. These are only needed on SMP systems, so use SMP barriers instead. Signed-off-by: Mike Frysinger <vapier@gentoo.org> Acked-by: Pavel Machek <pavel@ucw.cz> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
2010-12-24Freezer: Fix a race during freezing of TASK_STOPPED tasksTejun Heo
After calling freeze_task(), try_to_freeze_tasks() see whether the task is stopped or traced and if so, considers it to be frozen; however, nothing guarantees that either the task being frozen sees TIF_FREEZE or the freezer sees TASK_STOPPED -> TASK_RUNNING transition. The task being frozen may wake up and not see TIF_FREEZE while the freezer fails to notice the transition and believes the task is still stopped. This patch fixes the race by making freeze_task() always go through fake_signal_wake_up() for applicable tasks. The function goes through the target task's scheduler lock and thus guarantees that either the target sees TIF_FREEZE or try_to_freeze_task() sees TASK_RUNNING. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
2009-07-18sched: fix nr_uninterruptible accounting of frozen tasks reallyThomas Gleixner
commit e3c8ca8336 (sched: do not count frozen tasks toward load) broke the nr_uninterruptible accounting on freeze/thaw. On freeze the task is excluded from accounting with a check for (task->flags & PF_FROZEN), but that flag is cleared before the task is thawed. So while we prevent that the task with state TASK_UNINTERRUPTIBLE is accounted to nr_uninterruptible on freeze we decrement nr_uninterruptible on thaw. Use a separate flag which is handled by the freezing task itself. Set it before calling the scheduler with TASK_UNINTERRUPTIBLE state and clear it after we return from frozen state. Cc: <stable@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-10-30freezer_cg: use thaw_process() in unfreeze_cgroup()Li Zefan
Don't duplicate the implementation of thaw_process(). [akpm@linux-foundation.org: make __thaw_process() static] Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Cc: Cedric Le Goater <clg@fr.ibm.com> Acked-by: Matt Helsley <matthltc@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-10-20container freezer: implement freezer cgroup subsystemMatt Helsley
This patch implements a new freezer subsystem in the control groups framework. It provides a way to stop and resume execution of all tasks in a cgroup by writing in the cgroup filesystem. The freezer subsystem in the container filesystem defines a file named freezer.state. Writing "FROZEN" to the state file will freeze all tasks in the cgroup. Subsequently writing "RUNNING" will unfreeze the tasks in the cgroup. Reading will return the current state. * Examples of usage : # mkdir /containers/freezer # mount -t cgroup -ofreezer freezer /containers # mkdir /containers/0 # echo $some_pid > /containers/0/tasks to get status of the freezer subsystem : # cat /containers/0/freezer.state RUNNING to freeze all tasks in the container : # echo FROZEN > /containers/0/freezer.state # cat /containers/0/freezer.state FREEZING # cat /containers/0/freezer.state FROZEN to unfreeze all tasks in the container : # echo RUNNING > /containers/0/freezer.state # cat /containers/0/freezer.state RUNNING This is the basic mechanism which should do the right thing for user space task in a simple scenario. It's important to note that freezing can be incomplete. In that case we return EBUSY. This means that some tasks in the cgroup are busy doing something that prevents us from completely freezing the cgroup at this time. After EBUSY, the cgroup will remain partially frozen -- reflected by freezer.state reporting "FREEZING" when read. The state will remain "FREEZING" until one of these things happens: 1) Userspace cancels the freezing operation by writing "RUNNING" to the freezer.state file 2) Userspace retries the freezing operation by writing "FROZEN" to the freezer.state file (writing "FREEZING" is not legal and returns EIO) 3) The tasks that blocked the cgroup from entering the "FROZEN" state disappear from the cgroup's set of tasks. [akpm@linux-foundation.org: coding-style fixes] [akpm@linux-foundation.org: export thaw_process] Signed-off-by: Cedric Le Goater <clg@fr.ibm.com> Signed-off-by: Matt Helsley <matthltc@us.ibm.com> Acked-by: Serge E. Hallyn <serue@us.ibm.com> Tested-by: Matt Helsley <matthltc@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-10-20container freezer: make refrigerator always availableMatt Helsley
Now that the TIF_FREEZE flag is available in all architectures, extract the refrigerator() and freeze_task() from kernel/power/process.c and make it available to all. The refrigerator() can now be used in a control group subsystem implementing a control group freezer. Signed-off-by: Cedric Le Goater <clg@fr.ibm.com> Signed-off-by: Matt Helsley <matthltc@us.ibm.com> Acked-by: Serge E. Hallyn <serue@us.ibm.com> Tested-by: Matt Helsley <matthltc@us.ibm.com> Cc: "Rafael J. Wysocki" <rjw@sisk.pl> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>