From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, cmetcalf@mellanox.com,
cl@linux.com, lcapitulino@redhat.com, efault@gmx.de,
peterz@infradead.org, riel@redhat.com, tglx@linutronix.de,
kernellwp@gmail.com, mingo@kernel.org
Subject: Re: NO_HZ_FULL and tick running within a reasonable amount of time
Date: Tue, 3 Apr 2018 13:41:31 +0200 [thread overview]
Message-ID: <20180403114130.GA22765@lerouge> (raw)
In-Reply-To: <20180402220438.GA15885@linux.vnet.ibm.com>
On Mon, Apr 02, 2018 at 03:04:38PM -0700, Paul E. McKenney wrote:
> Hello!
>
> I am hitting the following on today's mainline under rcutorture, but
> only on scenarios built with CONFIG_NO_HZ_FULL=y:
>
> ------------------------------------------------------------------------
>
> WARNING: CPU: 0 PID: 7 at /home/paulmck/public_git/linux-rcu/kernel/sched/core.c:3124 sched_tick_remote+0x113/0x120
> Modules linked in:
> CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 4.16.0+ #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
> Workqueue: events_unbound sched_tick_remote
> RIP: 0010:sched_tick_remote+0x113/0x120
> RSP: 0018:ffff94d540103e20 EFLAGS: 00010002
> RAX: 000000012e9bb357 RBX: ffff8f95dfd21840 RCX: 000000000000001f
> RDX: 00000000b2d05e00 RSI: 00000000ffffffff RDI: ffff8f95dfd21858
> RBP: ffff94d540103e48 R08: 00000000f6499019 R09: 00000000f6499000
> R10: 00000000b163d33b R11: ffffffffa5c8c212 R12: ffff8f95dfd25518
> R13: ffff8f95de9e4200 R14: 0000000000003402 R15: ffff8f95dfd21858
> FS: 0000000000000000(0000) GS:ffff8f95dfc00000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000a015b40 CR3: 000000001de14000 CR4: 00000000000006f0
> Call Trace:
> process_one_work+0x1d9/0x6a0
> worker_thread+0x42/0x420
> kthread+0xf3/0x130
> ? rescuer_thread+0x340/0x340
> ? kthread_delayed_work_timer_fn+0x80/0x80
> ret_from_fork+0x3a/0x50
> Code: ff 48 8b 83 80 0b 00 00 48 85 c0 0f 85 41 ff ff ff e9 45 ff ff ff be ff ff ff ff 4c 89 ff e8 55 44 02 00 85 c0 75 87 0f 0b eb 83 <0f> 0b eb 97 66 0f 1f 84 00 00 00 00 00 41 57 41 56 41 55 41 54
> ---[ end trace fbdcbe529a8ae799 ]--
>
> ------------------------------------------------------------------------
>
> The WARN_ON_ONCE() triggering is this guy:
>
> delta = rq_clock_task(rq) - curr->se.exec_start;
> WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
Weird. Can you try to print up those values and see how much they drift?
if (WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3))
printk_once("clock_task: %lld exec_start: %lld\n", rq_clock_task(rq), curr->se.exec_start);
>
> But given that ->se.exec_start is zeroed from time to time, for example,
> in migrate_task_rq_fair(), I am a bit suspicious of this check.
>
> What am I missing here?
>
> Thanx, Paul
>
next prev parent reply other threads:[~2018-04-03 11:41 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-02 22:04 NO_HZ_FULL and tick running within a reasonable amount of time Paul E. McKenney
2018-04-03 9:23 ` Peter Zijlstra
2018-04-03 11:41 ` Frederic Weisbecker [this message]
2018-04-03 17:08 ` Paul E. McKenney
2018-04-07 13:52 ` Frederic Weisbecker
2018-04-23 13:04 ` Frederic Weisbecker
2018-04-23 13:26 ` Paul E. McKenney
2018-04-14 4:07 Jacek Tomaka
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