great, __schedule() doesn't need pay any attention to the TASK_DEAD now.
on 09/14/2016 12:37 AM, Peter Zijlstra wrote:
> On Tue, Sep 13, 2016 at 06:14:27PM +0200, Oleg Nesterov wrote:
>
>> Me too, and I failed to find something which could be broken... So
>> perhaps should make it nop and investigate the new bug reports after
>> that.
>
> Works for me :-)
>
>>
>> Hmm. And preempt_enable_no_resched_notrace() under TASK_DEAD in
>> __schedule() should be removed it seems, do_exit() can call __schedule()
>> directly.
>
>
> something like so?
>
> ---
>
> include/linux/kernel.h | 2 +-
> include/linux/sched.h | 2 ++
> kernel/exit.c | 11 ++---------
> kernel/sched/core.c | 23 ++++++++++++-----------
> 4 files changed, 17 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index d96a6118d26a..e5bd9cdd2e24 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -266,7 +266,7 @@ extern void oops_enter(void);
> extern void oops_exit(void);
> void print_oops_end_marker(void);
> extern int oops_may_print(void);
> -void do_exit(long error_code)
> +void __noreturn do_exit(long error_code)
> __noreturn;
> void complete_and_exit(struct completion *, long)
> __noreturn;
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index eb64fcd89e68..b0c818a05b2e 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -448,6 +448,8 @@ static inline void io_schedule(void)
> io_schedule_timeout(MAX_SCHEDULE_TIMEOUT);
> }
>
> +void __noreturn do_task_dead(void);
> +
> struct nsproxy;
> struct user_namespace;
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 091a78be3b09..d4c12692f766 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -725,7 +725,7 @@ static void check_stack_usage(void)
> static inline void check_stack_usage(void) {}
> #endif
>
> -void do_exit(long code)
> +void __noreturn do_exit(long code)
> {
> struct task_struct *tsk = current;
> int group_dead;
> @@ -897,14 +897,7 @@ void do_exit(long code)
> smp_mb();
> raw_spin_unlock_wait(&tsk->pi_lock);
>
> - /* causes final put_task_struct in finish_task_switch(). */
> - tsk->state = TASK_DEAD;
> - tsk->flags |= PF_NOFREEZE; /* tell freezer to ignore us */
> - schedule();
> - BUG();
> - /* Avoid "noreturn function does return". */
> - for (;;)
> - cpu_relax(); /* For when BUG is null */
> + do_task_dead();
> }
> EXPORT_SYMBOL_GPL(do_exit);
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a0086a5fc008..6034f269000f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3327,17 +3327,6 @@ static void __sched notrace __schedule(bool preempt)
> rq = cpu_rq(cpu);
> prev = rq->curr;
>
> - /*
> - * do_exit() calls schedule() with preemption disabled as an exception;
> - * however we must fix that up, otherwise the next task will see an
> - * inconsistent (higher) preempt count.
> - *
> - * It also avoids the below schedule_debug() test from complaining
> - * about this.
> - */
> - if (unlikely(prev->state == TASK_DEAD))
> - preempt_enable_no_resched_notrace();
> -
> schedule_debug(prev);
>
> if (sched_feat(HRTICK))
> @@ -3404,6 +3393,18 @@ static void __sched notrace __schedule(bool preempt)
> balance_callback(rq);
> }
>
> +void __noreturn do_task_dead(void)
> +{
> + /* causes final put_task_struct in finish_task_switch(). */
> + __set_current_state(TASK_DEAD);
> + current->flags |= PF_NOFREEZE; /* tell freezer to ignore us */
> + __schedule(false);
> + BUG();
> + /* Avoid "noreturn function does return". */
> + for (;;)
> + cpu_relax(); /* For when BUG is null */
> +}
> +
> static inline void sched_submit_work(struct task_struct *tsk)
> {
> if (!tsk->state || tsk_is_pi_blocked(tsk))
>
