On Sun 2016-10-09 08:04:03, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng...@hotmail.com>
>
> Commit:
>
> 10e2f1acd01 ("sched/core: Rewrite and improve select_idle_siblings()")
>
> ... improved select_idle_sibling() but also triggered a regression:
>
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000078
> IP: [<ffffffffb10cd332>] select_idle_sibling+0x1c2/0x4f0
> PGD 0
> Oops: 0000 [#1] SMP
> CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.8.0+ #16
> RIP: 0010:[<ffffffffb10cd332>] [<ffffffffb10cd332>]
> select_idle_sibling+0x1c2/0x4f0
> Call Trace:
> <IRQ>
> select_task_rq_fair+0x749/0x930
> ? select_task_rq_fair+0xb4/0x930
> ? __lock_is_held+0x54/0x70
> try_to_wake_up+0x19a/0x5b0
> default_wake_function+0x12/0x20
> autoremove_wake_function+0x12/0x40
> __wake_up_common+0x55/0x90
> __wake_up+0x39/0x50
> wake_up_klogd_work_func+0x40/0x60
> irq_work_run_list+0x57/0x80
> irq_work_run+0x2c/0x30
> smp_irq_work_interrupt+0x2e/0x40
> irq_work_interrupt+0x96/0xa0
> <EOI>
> ? _raw_spin_unlock_irqrestore+0x45/0x80
> try_to_wake_up+0x4a/0x5b0
> wake_up_state+0x10/0x20
> __kthread_unpark+0x67/0x70
> kthread_unpark+0x22/0x30
> cpuhp_online_idle+0x3e/0x70
> cpu_startup_entry+0x6a/0x450
> start_secondary+0x154/0x180
>
> This can be reproduced by running the ftrace test case of kselftest, the
> test case will hot-unplug the cpu and the cpu will attach to the NULL
> sched-domain during scheduler teardown.
>
> The step 2 for the rewrite select_idle_siblings():
>
> | Step 2) tracks the average cost of the scan and compares this to the
> | average idle time guestimate for the CPU doing the wakeup.
>
> If the cpu which doing the wakeup is the going hot-unplug cpu, then NULL
> sched domain will be dereferenced to acquire the average cost of the scan.
>
> This patch fix it by failing the search of an idle CPU in the LLC process
> if this sched domain is NULL.
>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Mike Galbraith <efa...@gmx.de>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
This patch helped me as well. I tested intel_powerclamp
conversion to the new CPU hotplug state machine. And this
problem was very easy to trigger.
Feel free to add
Tested-by: Petr Mladek <pmla...@suse.com>
Best Regards,
Petr
