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Commit 9acb7c07 authored by Quentin Perret's avatar Quentin Perret
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Revert "sched: Rework pick_next_task() slow-path" 



This reverts commit 67692435
temporarily in order to avoid the following splat:

[  222.515957] BUG: kernel NULL pointer dereference, address: 0000000000000040
[  222.518871] #PF: supervisor read access in kernel mode
[  222.518871] #PF: error_code(0x0000) - not-present page
[  222.518871] PGD 800000007cdf7067 P4D 800000007cdf7067 PUD 7c868067 PMD 0
[  222.518871] Oops: 0000 [#1] PREEMPT SMP PTI
[  222.518871] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 5.4.0-rc4-mainline-g6a9b34166c05 #1
[  222.518871] Hardware name: ChromiumOS crosvm, BIOS 0
[  222.518871] RIP: 0010:set_next_entity+0xf/0xf0
[  222.518871] Code: 42 0b e5 85 31 c0 e8 90 1a fc ff 0f 0b eb 9b 66 90 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 57 41 56 53 48 89 f3 49 89 fe <83> 7e 40 00 74 3d 4c 89 f7 48 89 de e8 80 f9 ff ff 4c 8d 7b 18 4d
[  222.518871] RSP: 0018:ffffb95040073de8 EFLAGS: 00010046
[  222.518871] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff85ec0c30
[  222.518871] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9ec44c728500
[  222.518871] RBP: ffffb95040073e00 R08: 0000000000000000 R09: 0000000000000000
[  222.518871] R10: 0000000000000000 R11: ffffffff84ef0a30 R12: 0000000000000000
[  222.518871] R13: 0000000000000000 R14: ffff9ec44c728500 R15: ffffb95040073e60
[  222.518871] FS:  0000000000000000(0000) GS:ffff9ec44c700000(0000) knlGS:0000000000000000
[  222.518871] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  222.518871] CR2: 0000000000000040 CR3: 000000007c87a002 CR4: 00000000003606e0
[  222.518871] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  222.518871] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  222.518871] Call Trace:
[  222.518871]  pick_next_task_fair+0xe8/0x410
[  222.518871]  ? rcu_note_context_switch+0x3ef/0x520
[  222.518871]  ? finish_task_switch+0x10d/0x250
[  222.518871]  __schedule+0x1f8/0x6e0
[  222.518871]  schedule_idle+0x27/0x40
[  222.518871]  do_idle+0x21c/0x240
[  222.518871]  cpu_startup_entry+0x25/0x30
[  222.518871]  start_secondary+0x18d/0x1b0
[  222.518871]  secondary_startup_64+0xa4/0xb0
[  222.518871] Modules linked in: vmw_vsock_virtio_transport vmw_vsock_virtio_transport_common vsock_diag vsock can_raw can snd_intel8x0 snd_ac97_codec ac97_bus virtio_input virtio_pci virtio_mmio virtio_crypto mmc_block mmc_core dummy_cpufreq rtc_test dummy_hcd can_dev vcan virtio_net net_failover failover virt_wifi virtio_blk virtio_gpu ttm virtio_rng virtio_ring virtio 8250_of crypto_engine
[  222.518871] CR2: 0000000000000040
[  222.518871] ---[ end trace ae741809965b22f2 ]---
[  222.518871] RIP: 0010:set_next_entity+0xf/0xf0
[  222.518871] Code: 42 0b e5 85 31 c0 e8 90 1a fc ff 0f 0b eb 9b 66 90 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 57 41 56 53 48 89 f3 49 89 fe <83> 7e 40 00 74 3d 4c 89 f7 48 89 de e8 80 f9 ff ff 4c 8d 7b 18 4d
[  222.518871] RSP: 0018:ffffb95040073de8 EFLAGS: 00010046
[  222.518871] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff85ec0c30
[  222.518871] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9ec44c728500
[  222.518871] RBP: ffffb95040073e00 R08: 0000000000000000 R09: 0000000000000000
[  222.518871] R10: 0000000000000000 R11: ffffffff84ef0a30 R12: 0000000000000000
[  222.518871] R13: 0000000000000000 R14: ffff9ec44c728500 R15: ffffb95040073e60
[  222.518871] FS:  0000000000000000(0000) GS:ffff9ec44c700000(0000) knlGS:0000000000000000
[  222.518871] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  222.518871] CR2: 0000000000000040 CR3: 000000007c87a002 CR4: 00000000003606e0
[  222.518871] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  222.518871] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  222.518871] Kernel panic - not syncing: Fatal exception
[  222.518871] Kernel Offset: 0x3e00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

Bug: 142182814
Test: 20/20 avd/avd_boot_test_kernel_triggered passing
Signed-off-by: default avatarQuentin Perret <qperret@google.com>
Change-Id: I62bb09b4710fdc593cbf1f42bf4bbc066e401458
parent 50118fa8

kernel/sched/core.c

+7 −12
Original line number Diff line number Diff line
@@ -3919,7 +3919,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 


		p = fair_sched_class.pick_next_task(rq, prev, rf);

		if (unlikely(p == RETRY_TASK))

			goto restart;

			goto again;



		/* Assumes fair_sched_class->next == idle_sched_class */

		if (unlikely(!p))
@@ -3928,20 +3928,15 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 
		return p;

	}



restart:

	/*

	 * Ensure that we put DL/RT tasks before the pick loop, such that they

	 * can PULL higher prio tasks when we lower the RQ 'priority'.

	 */

	prev->sched_class->put_prev_task(rq, prev, rf);

	if (!rq->nr_running)

		newidle_balance(rq, rf);



again:

	for_each_class(class) {

		p = class->pick_next_task(rq, NULL, NULL);

		if (p)

		p = class->pick_next_task(rq, prev, rf);

		if (p) {

			if (unlikely(p == RETRY_TASK))

				goto again;

			return p;

		}

	}



	/* The idle class should always have a runnable task: */

	BUG();

kernel/sched/deadline.c

+28 −2
Original line number Diff line number Diff line
@@ -1761,13 +1761,39 @@ pick_next_task_dl(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 
	struct task_struct *p;

	struct dl_rq *dl_rq;



	WARN_ON_ONCE(prev || rf);



	dl_rq = &rq->dl;



	if (need_pull_dl_task(rq, prev)) {

		/*

		 * This is OK, because current is on_cpu, which avoids it being

		 * picked for load-balance and preemption/IRQs are still

		 * disabled avoiding further scheduler activity on it and we're

		 * being very careful to re-start the picking loop.

		 */

		rq_unpin_lock(rq, rf);

		pull_dl_task(rq);

		rq_repin_lock(rq, rf);

		/*

		 * pull_dl_task() can drop (and re-acquire) rq->lock; this

		 * means a stop task can slip in, in which case we need to

		 * re-start task selection.

		 */

		if (rq->stop && task_on_rq_queued(rq->stop))

			return RETRY_TASK;

	}



	/*

	 * When prev is DL, we may throttle it in put_prev_task().

	 * So, we update time before we check for dl_nr_running.

	 */

	if (prev->sched_class == &dl_sched_class)

		update_curr_dl(rq);



	if (unlikely(!dl_rq->dl_nr_running))

		return NULL;



	put_prev_task(rq, prev);



	dl_se = pick_next_dl_entity(rq, dl_rq);

	BUG_ON(!dl_se);

kernel/sched/fair.c

+3 −6
Original line number Diff line number Diff line
@@ -6810,7 +6810,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf 
		goto idle;



#ifdef CONFIG_FAIR_GROUP_SCHED

	if (!prev || prev->sched_class != &fair_sched_class)

	if (prev->sched_class != &fair_sched_class)

		goto simple;



	/*
@@ -6887,7 +6887,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf 
	goto done;

simple:

#endif

	if (prev)



	put_prev_task(rq, prev);



	do {
@@ -6916,9 +6916,6 @@ done: __maybe_unused; 
	return p;



idle:

	if (!rf)

		return NULL;



	new_tasks = newidle_balance(rq, rf);



	/*

kernel/sched/idle.c

+1 −3
Original line number Diff line number Diff line
@@ -390,9 +390,7 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf 
{

	struct task_struct *next = rq->idle;



	if (prev)

	put_prev_task(rq, prev);



	set_next_task_idle(rq, next);



	return next;

kernel/sched/rt.c

+28 −1
Original line number Diff line number Diff line
@@ -1554,11 +1554,38 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) 
	struct task_struct *p;

	struct rt_rq *rt_rq = &rq->rt;



	WARN_ON_ONCE(prev || rf);

	if (need_pull_rt_task(rq, prev)) {

		/*

		 * This is OK, because current is on_cpu, which avoids it being

		 * picked for load-balance and preemption/IRQs are still

		 * disabled avoiding further scheduler activity on it and we're

		 * being very careful to re-start the picking loop.

		 */

		rq_unpin_lock(rq, rf);

		pull_rt_task(rq);

		rq_repin_lock(rq, rf);

		/*

		 * pull_rt_task() can drop (and re-acquire) rq->lock; this

		 * means a dl or stop task can slip in, in which case we need

		 * to re-start task selection.

		 */

		if (unlikely((rq->stop && task_on_rq_queued(rq->stop)) ||

			     rq->dl.dl_nr_running))

			return RETRY_TASK;

	}



	/*

	 * We may dequeue prev's rt_rq in put_prev_task().

	 * So, we update time before rt_queued check.

	 */

	if (prev->sched_class == &rt_sched_class)

		update_curr_rt(rq);



	if (!rt_rq->rt_queued)

		return NULL;



	put_prev_task(rq, prev);



	p = _pick_next_task_rt(rq);



	set_next_task_rt(rq, p);