Re: [RFC v4][PATCH part-1 5/7] mm/asi: Exit/enter ASI when task enters/exits scheduler

[kbuild test robot <lkp@intel.com>]

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Hi Alexandre,

[FYI, it's a private test report for your RFC patch.]
[auto build test ERROR on tip/x86/asm]
[also build test ERROR on tip/x86/core v5.7-rc4]
[cannot apply to tip/x86/mm next-20200504]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Alexandre-Chartre/ASI-Part-I-ASI-Infrastructure-and-PTI/20200505-074555
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 2ce0d7f9766f0e49bb54f149c77bae89464932fb
config: um-x86_64_defconfig (attached as .config)
compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=um SUBARCH=x86_64

If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   kernel//sched/core.c: In function '__schedule':
>> kernel//sched/core.c:4022:3: error: implicit declaration of function 'asi_schedule_out'; did you mean '__schedule_bug'? [-Werror=implicit-function-declaration]
      asi_schedule_out(current);
      ^~~~~~~~~~~~~~~~
      __schedule_bug
>> kernel//sched/core.c:4111:3: error: implicit declaration of function 'asi_schedule_in'; did you mean '__schedule'? [-Werror=implicit-function-declaration]
      asi_schedule_in(current);
      ^~~~~~~~~~~~~~~
      __schedule
   cc1: some warnings being treated as errors

vim +4022 kernel//sched/core.c

  3968	
  3969	/*
  3970	 * __schedule() is the main scheduler function.
  3971	 *
  3972	 * The main means of driving the scheduler and thus entering this function are:
  3973	 *
  3974	 *   1. Explicit blocking: mutex, semaphore, waitqueue, etc.
  3975	 *
  3976	 *   2. TIF_NEED_RESCHED flag is checked on interrupt and userspace return
  3977	 *      paths. For example, see arch/x86/entry_64.S.
  3978	 *
  3979	 *      To drive preemption between tasks, the scheduler sets the flag in timer
  3980	 *      interrupt handler scheduler_tick().
  3981	 *
  3982	 *   3. Wakeups don't really cause entry into schedule(). They add a
  3983	 *      task to the run-queue and that's it.
  3984	 *
  3985	 *      Now, if the new task added to the run-queue preempts the current
  3986	 *      task, then the wakeup sets TIF_NEED_RESCHED and schedule() gets
  3987	 *      called on the nearest possible occasion:
  3988	 *
  3989	 *       - If the kernel is preemptible (CONFIG_PREEMPTION=y):
  3990	 *
  3991	 *         - in syscall or exception context, at the next outmost
  3992	 *           preempt_enable(). (this might be as soon as the wake_up()'s
  3993	 *           spin_unlock()!)
  3994	 *
  3995	 *         - in IRQ context, return from interrupt-handler to
  3996	 *           preemptible context
  3997	 *
  3998	 *       - If the kernel is not preemptible (CONFIG_PREEMPTION is not set)
  3999	 *         then at the next:
  4000	 *
  4001	 *          - cond_resched() call
  4002	 *          - explicit schedule() call
  4003	 *          - return from syscall or exception to user-space
  4004	 *          - return from interrupt-handler to user-space
  4005	 *
  4006	 * WARNING: must be called with preemption disabled!
  4007	 */
  4008	static void __sched notrace __schedule(bool preempt)
  4009	{
  4010		struct task_struct *prev, *next;
  4011		unsigned long *switch_count;
  4012		struct rq_flags rf;
  4013		struct rq *rq;
  4014		int cpu;
  4015	
  4016		/*
  4017		 * If the task is using ASI then exit it right away otherwise the
  4018		 * ASI will likely quickly fault, for example when accessing run
  4019		 * queues.
  4020		 */
  4021		if (IS_ENABLED(CONFIG_ADDRESS_SPACE_ISOLATION))
> 4022			asi_schedule_out(current);
  4023	
  4024		cpu = smp_processor_id();
  4025		rq = cpu_rq(cpu);
  4026		prev = rq->curr;
  4027	
  4028		schedule_debug(prev, preempt);
  4029	
  4030		if (sched_feat(HRTICK))
  4031			hrtick_clear(rq);
  4032	
  4033		local_irq_disable();
  4034		rcu_note_context_switch(preempt);
  4035	
  4036		/*
  4037		 * Make sure that signal_pending_state()->signal_pending() below
  4038		 * can't be reordered with __set_current_state(TASK_INTERRUPTIBLE)
  4039		 * done by the caller to avoid the race with signal_wake_up().
  4040		 *
  4041		 * The membarrier system call requires a full memory barrier
  4042		 * after coming from user-space, before storing to rq->curr.
  4043		 */
  4044		rq_lock(rq, &rf);
  4045		smp_mb__after_spinlock();
  4046	
  4047		/* Promote REQ to ACT */
  4048		rq->clock_update_flags <<= 1;
  4049		update_rq_clock(rq);
  4050	
  4051		switch_count = &prev->nivcsw;
  4052		if (!preempt && prev->state) {
  4053			if (signal_pending_state(prev->state, prev)) {
  4054				prev->state = TASK_RUNNING;
  4055			} else {
  4056				deactivate_task(rq, prev, DEQUEUE_SLEEP | DEQUEUE_NOCLOCK);
  4057	
  4058				if (prev->in_iowait) {
  4059					atomic_inc(&rq->nr_iowait);
  4060					delayacct_blkio_start();
  4061				}
  4062			}
  4063			switch_count = &prev->nvcsw;
  4064		}
  4065	
  4066		next = pick_next_task(rq, prev, &rf);
  4067		clear_tsk_need_resched(prev);
  4068		clear_preempt_need_resched();
  4069	
  4070		if (likely(prev != next)) {
  4071			rq->nr_switches++;
  4072			/*
  4073			 * RCU users of rcu_dereference(rq->curr) may not see
  4074			 * changes to task_struct made by pick_next_task().
  4075			 */
  4076			RCU_INIT_POINTER(rq->curr, next);
  4077			/*
  4078			 * The membarrier system call requires each architecture
  4079			 * to have a full memory barrier after updating
  4080			 * rq->curr, before returning to user-space.
  4081			 *
  4082			 * Here are the schemes providing that barrier on the
  4083			 * various architectures:
  4084			 * - mm ? switch_mm() : mmdrop() for x86, s390, sparc, PowerPC.
  4085			 *   switch_mm() rely on membarrier_arch_switch_mm() on PowerPC.
  4086			 * - finish_lock_switch() for weakly-ordered
  4087			 *   architectures where spin_unlock is a full barrier,
  4088			 * - switch_to() for arm64 (weakly-ordered, spin_unlock
  4089			 *   is a RELEASE barrier),
  4090			 */
  4091			++*switch_count;
  4092	
  4093			psi_sched_switch(prev, next, !task_on_rq_queued(prev));
  4094	
  4095			trace_sched_switch(preempt, prev, next);
  4096	
  4097			/* Also unlocks the rq: */
  4098			rq = context_switch(rq, prev, next, &rf);
  4099		} else {
  4100			rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
  4101			rq_unlock_irq(rq, &rf);
  4102		}
  4103	
  4104		balance_callback(rq);
  4105	
  4106		/*
  4107		 * Now the task will resume execution, we can safely return to
  4108		 * its ASI if one was in used.
  4109		 */
  4110		if (IS_ENABLED(CONFIG_ADDRESS_SPACE_ISOLATION))
> 4111			asi_schedule_in(current);
  4112	}
  4113	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org

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