Messages in this thread Patch in this message | | | Date | Fri, 28 Apr 2023 18:17:58 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH v7 1/3] sched/core: warn on call put_task_struct in invalid context |
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On 2023-04-25 08:43:01 [-0300], Wander Lairson Costa wrote: > Under PREEMPT_RT, spinlocks become sleepable locks. put_task_struct() > indirectly acquires a spinlock. Therefore, it can't be called in > atomic/interrupt context in RT kernels. > > To prevent such conditions, add a check for atomic/interrupt context > before calling put_task_struct(). > > Signed-off-by: Wander Lairson Costa <wander@redhat.com> > Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Been only CCed here.
I asked to not special case PREEMPT_RT but doing this (clean up via RCU) unconditionally. I don't remember that someone said "this is a bad because $reason".
Lockdep will complain about this on !RT.
The below open codes rtlock_might_resched() with no explanation on why it works or where it comes from.
The function is named put_task_struct_atomic_safe() yet it behaves it differently on PREEMPT_RT otherwise it remains put_task_struct().
Not good.
> --- > include/linux/sched/task.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h > index 357e0068497c..b597b97b1f8f 100644 > --- a/include/linux/sched/task.h > +++ b/include/linux/sched/task.h > @@ -113,14 +113,28 @@ static inline struct task_struct *get_task_struct(struct task_struct *t) > > extern void __put_task_struct(struct task_struct *t); > > +#define PUT_TASK_RESCHED_OFFSETS \ > + (rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT) > + > +#define __put_task_might_resched() \ > + __might_resched(__FILE__, __LINE__, PUT_TASK_RESCHED_OFFSETS) > + > +#define put_task_might_resched() \ > + do { \ > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) \ > + __put_task_might_resched(); \ > + } while (0) > + > static inline void put_task_struct(struct task_struct *t) > { > + put_task_might_resched(); > if (refcount_dec_and_test(&t->usage)) > __put_task_struct(t); > } > > static inline void put_task_struct_many(struct task_struct *t, int nr) > { > + put_task_might_resched(); > if (refcount_sub_and_test(nr, &t->usage)) > __put_task_struct(t); > } > -- > 2.40.0 >
Sebastian
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