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authorPeter Zijlstra <peterz@infradead.org>2018-06-07 11:45:49 +0200
committerIngo Molnar <mingo@kernel.org>2018-07-03 09:17:30 +0200
commit1cef1150ef40ec52f507436a14230cbc2623299c (patch)
tree911e4ed753fbd700d16aaa0efd93767c26684d65 /include
parent3482d98bbc730758b63a5d1cf41d05ea17481412 (diff)
downloadlinux-1cef1150ef40ec52f507436a14230cbc2623299c.tar.bz2
kthread, sched/core: Fix kthread_parkme() (again...)
Gaurav reports that commit: 85f1abe0019f ("kthread, sched/wait: Fix kthread_parkme() completion issue") isn't working for him. Because of the following race: > controller Thread CPUHP Thread > takedown_cpu > kthread_park > kthread_parkme > Set KTHREAD_SHOULD_PARK > smpboot_thread_fn > set Task interruptible > > > wake_up_process > if (!(p->state & state)) > goto out; > > Kthread_parkme > SET TASK_PARKED > schedule > raw_spin_lock(&rq->lock) > ttwu_remote > waiting for __task_rq_lock > context_switch > > finish_lock_switch > > > > Case TASK_PARKED > kthread_park_complete > > > SET Running Furthermore, Oleg noticed that the whole scheduler TASK_PARKED handling is buggered because the TASK_DEAD thing is done with preemption disabled, the current code can still complete early on preemption :/ So basically revert that earlier fix and go with a variant of the alternative mentioned in the commit. Promote TASK_PARKED to special state to avoid the store-store issue on task->state leading to the WARN in kthread_unpark() -> __kthread_bind(). But in addition, add wait_task_inactive() to kthread_park() to ensure the task really is PARKED when we return from kthread_park(). This avoids the whole kthread still gets migrated nonsense -- although it would be really good to get this done differently. Reported-by: Gaurav Kohli <gkohli@codeaurora.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Fixes: 85f1abe0019f ("kthread, sched/wait: Fix kthread_parkme() completion issue") Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/kthread.h1
-rw-r--r--include/linux/sched.h2
2 files changed, 1 insertions, 2 deletions
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 2803264c512f..c1961761311d 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -62,7 +62,6 @@ void *kthread_probe_data(struct task_struct *k);
int kthread_park(struct task_struct *k);
void kthread_unpark(struct task_struct *k);
void kthread_parkme(void);
-void kthread_park_complete(struct task_struct *k);
int kthreadd(void *unused);
extern struct task_struct *kthreadd_task;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9256118bd40c..43731fe51c97 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -118,7 +118,7 @@ struct task_group;
* the comment with set_special_state().
*/
#define is_special_task_state(state) \
- ((state) & (__TASK_STOPPED | __TASK_TRACED | TASK_DEAD))
+ ((state) & (__TASK_STOPPED | __TASK_TRACED | TASK_PARKED | TASK_DEAD))
#define __set_current_state(state_value) \
do { \