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From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
To: Vineeth Remanan Pillai <vpillai@digitalocean.com>
Cc: Nishanth Aravamudan <naravamudan@digitalocean.com>,
	Julien Desfossez <jdesfossez@digitalocean.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	mingo@kernel.org, tglx@linutronix.de, pjt@google.com,
	torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
	subhra.mazumdar@oracle.com, fweisbec@gmail.com,
	keescook@chromium.org, kerrnel@google.com,
	Phil Auld <pauld@redhat.com>, Aaron Lu <aaron.lwe@gmail.com>,
	Aubrey Li <aubrey.intel@gmail.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [RFC PATCH v3 13/16] sched: Add core wide task selection and scheduling.
Date: Fri, 7 Jun 2019 16:36:56 -0700	[thread overview]
Message-ID: <20190607233656.GB12952@guptapadev.amr> (raw)
In-Reply-To: <f7d51cdfc5672677084e0f4b01b28eabbcdd99a6.1559129225.git.vpillai@digitalocean.com>

On Wed, May 29, 2019 at 08:36:49PM +0000, Vineeth Remanan Pillai wrote:
> From: Peter Zijlstra <peterz@infradead.org>
> 
> Instead of only selecting a local task, select a task for all SMT
> siblings for every reschedule on the core (irrespective which logical
> CPU does the reschedule).
> 
> NOTE: there is still potential for siblings rivalry.
> NOTE: this is far too complicated; but thus far I've failed to
>       simplify it further.

Looks like there are still some race conditions while bringing cpu
online/offline. I am seeing an easy to reproduce panic when turning SMT on/off
in a loop with core scheduling ON. I dont see the panic with core scheduling
OFF.

Steps to reproduce:

mkdir /sys/fs/cgroup/cpu/group1
mkdir /sys/fs/cgroup/cpu/group2
echo 1 > /sys/fs/cgroup/cpu/group1/cpu.tag
echo 1 > /sys/fs/cgroup/cpu/group2/cpu.tag

echo $$ > /sys/fs/cgroup/cpu/group1/tasks

while [ 1 ];  do
	echo on	 > /sys/devices/system/cpu/smt/control
	echo off > /sys/devices/system/cpu/smt/control
done

Panic logs:
[  274.629437] BUG: unable to handle kernel NULL pointer dereference at
0000000000000024
[  274.630366] #PF error: [normal kernel read fault]
[  274.630933] PGD 800000003e52c067 P4D 800000003e52c067 PUD 0
[  274.631613] Oops: 0000 [#1] SMP PTI
[  274.632016] CPU: 0 PID: 1470 Comm: bash Tainted: G        W
5.1.4+ #33
[  274.632854] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS ?-20180724_192412-buildhw-07.phx2.fedoraproject.org-1.fc29
04/01/2014
[  274.634248] RIP: 0010:__schedule+0x9d4/0x1350
[  274.634699] Code: da 0f 83 21 04 00 00 48 8b 35 70 f3 ab 00 48 c7 c7
51 1c a8 81 e8 4c 4e 6b ff 49 8b 85 b8 0b 00 00 48 85 c0 0f 84 2f 09 00
01
[  274.636648] RSP: 0018:ffffc900008f3ca8 EFLAGS: 00010046
[  274.637197] RAX: 0000000000000000 RBX: 0000000000000001 RCX:
0000000000000040
[  274.637941] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
ffffffff82544890
[  274.638691] RBP: ffffc900008f3d40 R08: 00000000000004c7 R09:
0000000000000030
[  274.639449] R10: 0000000000000001 R11: ffffc900008f3b28 R12:
ffff88803d2d0e80
[  274.640172] R13: ffff88803eaa0a40 R14: ffff88803ea20a40 R15:
ffff88803d2d0e80
[  274.640915] FS:  0000000000000000(0000) GS:ffff88803ea00000(0063)
knlGS:00000000f7f8b780
[  274.641755] CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
[  274.642355] CR2: 0000000000000024 CR3: 000000003c01a005 CR4:
0000000000360ef0
[  274.643135] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[  274.643995] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[  274.645023] Call Trace:
[  274.645336]  schedule+0x28/0x70
[  274.645621]  native_cpu_up+0x271/0x6d0
[  274.645959]  ? cpus_read_trylock+0x40/0x40
[  274.646324]  bringup_cpu+0x2d/0xe0
[  274.646631]  cpuhp_invoke_callback+0x94/0x550
[  274.647032]  ? ring_buffer_record_is_set_on+0x10/0x10
[  274.647478]  _cpu_up+0xa9/0x140
[  274.647763]  store_smt_control+0x1cb/0x260
[  274.648132]  kernfs_fop_write+0x108/0x190
[  274.648498]  vfs_write+0xa5/0x1a0
[  274.648794]  ksys_write+0x57/0xd0
[  274.649100]  do_fast_syscall_32+0x92/0x220
[  274.649468]  entry_SYSENTER_compat+0x7c/0x8e


NULL pointer exception is triggered when sibling is offline during core task
pick in pick_next_task() leaving rq_i->core_pick = NULL and if sibling comes
online before the "Reschedule siblings" block in the same function it causes
panic in is_idle_task(rq_i->core_pick).

Traces for the scenario:
[ 274.599567] bash-1470 0d... 273921815us : __schedule: cpu(0) is online during core_pick 
[ 274.600339] bash-1470 0d... 273921816us : __schedule: cpu(1) is offline during core_pick 
[ 274.601106] bash-1470 0d... 273921816us : __schedule: picked: bash/1470 ffff88803cb9c000 
[ 274.602106] bash-1470 0d... 273921816us : __schedule: cpu(0) is online.. during Reschedule siblings 
[ 274.603219] bash-1470 0d... 273921816us : __schedule: cpu(1) is online.. during Reschedule siblings 
[ 274.604333] <idle>-0 1d... 273921816us : start_secondary: cpu(1) is online now 
[ 274.605239] bash-1470 0d... 273922148us : __schedule: rq_i->core_pick on cpu(1) is NULL

I am not able to reproduce the panic after the below change. Not sure if this
is the right fix. Maybe we don't have to allow cpus to go online/offline while
pick_next_task() is executing.

-------------- 8< ---------------
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 90655c9ad937..b230b095772a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3874,7 +3874,7 @@ next_class:;
        for_each_cpu(i, smt_mask) {
                struct rq *rq_i = cpu_rq(i);
 
-               if (cpu_is_offline(i))
+               if (cpu_is_offline(i) || !rq_i->core_pick)
                        continue;
 
                WARN_ON_ONCE(!rq_i->core_pick);

  reply	other threads:[~2019-06-07 23:39 UTC|newest]

Thread overview: 161+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-29 20:36 [RFC PATCH v3 00/16] Core scheduling v3 Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 01/16] stop_machine: Fix stop_cpus_in_progress ordering Vineeth Remanan Pillai
2019-08-08 10:54   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-08-26 16:19   ` [RFC PATCH v3 01/16] " mark gross
2019-08-26 16:59     ` Peter Zijlstra
2019-05-29 20:36 ` [RFC PATCH v3 02/16] sched: Fix kerneldoc comment for ia64_set_curr_task Vineeth Remanan Pillai
2019-08-08 10:55   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-08-26 16:20   ` [RFC PATCH v3 02/16] " mark gross
2019-05-29 20:36 ` [RFC PATCH v3 03/16] sched: Wrap rq::lock access Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 04/16] sched/{rt,deadline}: Fix set_next_task vs pick_next_task Vineeth Remanan Pillai
2019-08-08 10:55   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-05-29 20:36 ` [RFC PATCH v3 05/16] sched: Add task_struct pointer to sched_class::set_curr_task Vineeth Remanan Pillai
2019-08-08 10:57   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-05-29 20:36 ` [RFC PATCH v3 06/16] sched/fair: Export newidle_balance() Vineeth Remanan Pillai
2019-08-08 10:58   ` [tip:sched/core] sched/fair: Expose newidle_balance() tip-bot for Peter Zijlstra
2019-05-29 20:36 ` [RFC PATCH v3 07/16] sched: Allow put_prev_task() to drop rq->lock Vineeth Remanan Pillai
2019-08-08 10:58   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-08-26 16:51   ` [RFC PATCH v3 07/16] " mark gross
2019-05-29 20:36 ` [RFC PATCH v3 08/16] sched: Rework pick_next_task() slow-path Vineeth Remanan Pillai
2019-08-08 10:59   ` [tip:sched/core] " tip-bot for Peter Zijlstra
2019-08-26 17:01   ` [RFC PATCH v3 08/16] " mark gross
2019-05-29 20:36 ` [RFC PATCH v3 09/16] sched: Introduce sched_class::pick_task() Vineeth Remanan Pillai
2019-08-26 17:14   ` mark gross
2019-05-29 20:36 ` [RFC PATCH v3 10/16] sched: Core-wide rq->lock Vineeth Remanan Pillai
2019-05-31 11:08   ` Peter Zijlstra
2019-05-31 15:23     ` Vineeth Pillai
2019-05-29 20:36 ` [RFC PATCH v3 11/16] sched: Basic tracking of matching tasks Vineeth Remanan Pillai
2019-08-26 20:59   ` mark gross
2019-05-29 20:36 ` [RFC PATCH v3 12/16] sched: A quick and dirty cgroup tagging interface Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 13/16] sched: Add core wide task selection and scheduling Vineeth Remanan Pillai
2019-06-07 23:36   ` Pawan Gupta [this message]
2019-05-29 20:36 ` [RFC PATCH v3 14/16] sched/fair: Add a few assertions Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 15/16] sched: Trivial forced-newidle balancer Vineeth Remanan Pillai
2019-05-29 20:36 ` [RFC PATCH v3 16/16] sched: Debug bits Vineeth Remanan Pillai
2019-05-29 21:02   ` Peter Oskolkov
2019-05-30 14:04 ` [RFC PATCH v3 00/16] Core scheduling v3 Aubrey Li
2019-05-30 14:17   ` Julien Desfossez
2019-05-31  4:55     ` Aubrey Li
2019-05-31  3:01   ` Aaron Lu
2019-05-31  5:12     ` Aubrey Li
2019-05-31  6:09       ` Aaron Lu
2019-05-31  6:53         ` Aubrey Li
2019-05-31  7:44           ` Aaron Lu
2019-05-31  8:26             ` Aubrey Li
2019-05-31 21:08     ` Julien Desfossez
2019-06-06 15:26       ` Julien Desfossez
2019-06-12  1:52         ` Li, Aubrey
2019-06-12 16:06           ` Julien Desfossez
2019-06-12 16:33         ` Julien Desfossez
2019-06-13  0:03           ` Subhra Mazumdar
2019-06-13  3:22             ` Julien Desfossez
2019-06-17  2:51               ` Aubrey Li
2019-06-19 18:33                 ` Julien Desfossez
2019-07-18 10:07                   ` Aaron Lu
2019-07-18 23:27                     ` Tim Chen
2019-07-19  5:52                       ` Aaron Lu
2019-07-19 11:48                         ` Aubrey Li
2019-07-19 18:33                         ` Tim Chen
2019-07-22 10:26                     ` Aubrey Li
2019-07-22 10:43                       ` Aaron Lu
2019-07-23  2:52                         ` Aubrey Li
2019-07-25 14:30                       ` Aaron Lu
2019-07-25 14:31                         ` [RFC PATCH 1/3] wrapper for cfs_rq->min_vruntime Aaron Lu
2019-07-25 14:32                         ` [PATCH 2/3] core vruntime comparison Aaron Lu
2019-08-06 14:17                           ` Peter Zijlstra
2019-07-25 14:33                         ` [PATCH 3/3] temp hack to make tick based schedule happen Aaron Lu
2019-07-25 21:42                         ` [RFC PATCH v3 00/16] Core scheduling v3 Li, Aubrey
2019-07-26 15:21                         ` Julien Desfossez
2019-07-26 21:29                           ` Tim Chen
2019-07-31  2:42                           ` Li, Aubrey
2019-08-02 15:37                             ` Julien Desfossez
2019-08-05 15:55                               ` Tim Chen
2019-08-06  3:24                                 ` Aaron Lu
2019-08-06  6:56                                   ` Aubrey Li
2019-08-06  7:04                                     ` Aaron Lu
2019-08-06 12:24                                       ` Vineeth Remanan Pillai
2019-08-06 13:49                                         ` Aaron Lu
2019-08-06 16:14                                           ` Vineeth Remanan Pillai
2019-08-06 14:16                                         ` Peter Zijlstra
2019-08-06 15:53                                           ` Vineeth Remanan Pillai
2019-08-06 17:03                                   ` Tim Chen
2019-08-06 17:12                                     ` Peter Zijlstra
2019-08-06 21:19                                       ` Tim Chen
2019-08-08  6:47                                         ` Aaron Lu
2019-08-08 17:27                                           ` Tim Chen
2019-08-08 21:42                                             ` Tim Chen
2019-08-10 14:15                                               ` Aaron Lu
2019-08-12 15:38                                                 ` Vineeth Remanan Pillai
2019-08-13  2:24                                                   ` Aaron Lu
2019-08-08 12:55                                 ` Aaron Lu
2019-08-08 16:39                                   ` Tim Chen
2019-08-10 14:18                                     ` Aaron Lu
2019-08-05 20:09                               ` Phil Auld
2019-08-06 13:54                                 ` Aaron Lu
2019-08-06 14:17                                   ` Phil Auld
2019-08-06 14:41                                     ` Aaron Lu
2019-08-06 14:55                                       ` Phil Auld
2019-08-07  8:58                               ` Dario Faggioli
2019-08-07 17:10                                 ` Tim Chen
2019-08-15 16:09                                   ` Dario Faggioli
2019-08-16  2:33                                     ` Aaron Lu
2019-09-05  1:44                                   ` Julien Desfossez
2019-09-06 22:17                                     ` Tim Chen
2019-09-18 21:27                                     ` Tim Chen
2019-09-06 18:30                                   ` Tim Chen
2019-09-11 14:02                                     ` Aaron Lu
2019-09-11 16:19                                       ` Tim Chen
2019-09-11 16:47                                         ` Vineeth Remanan Pillai
2019-09-12 12:35                                           ` Aaron Lu
2019-09-12 17:29                                             ` Tim Chen
2019-09-13 14:15                                               ` Aaron Lu
2019-09-13 17:13                                                 ` Tim Chen
2019-09-30 11:53                                             ` Vineeth Remanan Pillai
2019-10-02 20:48                                               ` Vineeth Remanan Pillai
2019-10-10 13:54                                                 ` Aaron Lu
2019-10-10 14:29                                                   ` Vineeth Remanan Pillai
2019-10-11  7:33                                                     ` Aaron Lu
2019-10-11 11:32                                                       ` Vineeth Remanan Pillai
2019-10-11 12:01                                                         ` Aaron Lu
2019-10-11 12:10                                                           ` Vineeth Remanan Pillai
2019-10-12  3:55                                                             ` Aaron Lu
2019-10-13 12:44                                                               ` Vineeth Remanan Pillai
2019-10-14  9:57                                                                 ` Aaron Lu
2019-10-21 12:30                                                                   ` Vineeth Remanan Pillai
2019-09-12 12:04                                         ` Aaron Lu
2019-09-12 17:05                                           ` Tim Chen
2019-09-13 13:57                                             ` Aaron Lu
2019-09-12 23:12                                           ` Aubrey Li
2019-09-15 14:14                                             ` Aaron Lu
2019-09-18  1:33                                               ` Aubrey Li
2019-09-18 20:40                                                 ` Tim Chen
2019-09-18 22:16                                                   ` Aubrey Li
2019-09-30 14:36                                                     ` Vineeth Remanan Pillai
2019-10-29 20:40                                                   ` Julien Desfossez
2019-11-01 21:42                                                     ` Tim Chen
2019-10-29  9:11                                               ` Dario Faggioli
2019-10-29  9:15                                                 ` Dario Faggioli
2019-10-29  9:16                                                 ` Dario Faggioli
2019-10-29  9:17                                                 ` Dario Faggioli
2019-10-29  9:18                                                 ` Dario Faggioli
2019-10-29  9:18                                                 ` Dario Faggioli
2019-10-29  9:19                                                 ` Dario Faggioli
2019-10-29  9:20                                                 ` Dario Faggioli
2019-10-29 20:34                                                   ` Julien Desfossez
2019-11-15 16:30                                                     ` Dario Faggioli
2019-09-25  2:40                                     ` Aubrey Li
2019-09-25 17:24                                       ` Tim Chen
2019-09-25 22:07                                         ` Aubrey Li
2019-09-30 15:22                                     ` Julien Desfossez
2019-08-27 21:14 ` Matthew Garrett
2019-08-27 21:50   ` Peter Zijlstra
2019-08-28 15:30     ` Phil Auld
2019-08-28 16:01       ` Peter Zijlstra
2019-08-28 16:37         ` Tim Chen
2019-08-29 14:30         ` Phil Auld
2019-08-29 14:38           ` Peter Zijlstra
2019-09-10 14:27             ` Julien Desfossez
2019-09-18 21:12               ` Tim Chen
2019-08-28 15:59     ` Tim Chen
2019-08-28 16:16       ` Peter Zijlstra
2019-08-27 23:24   ` Aubrey Li

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