Hi Ingo,
On 07/05/2014 04:13 PM, tip-bot for Peter Zijlstra wrote:
> Commit-ID: a77353e5eb56b6c6098bfce59aff1f449451b0b7
> Gitweb: http://git.kernel.org/tip/a77353e5eb56b6c6098bfce59aff1f449451b0b7
> Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> AuthorDate: Wed, 25 Jun 2014 07:13:07 +0200
> Committer: Ingo Molnar <mingo@xxxxxxxxxx>
> CommitDate: Sat, 5 Jul 2014 11:17:26 +0200
>
> irq_work: Remove BUG_ON in irq_work_run()
>
I believe this fix has to go into 3.16 itself, since this fixes a CPU hotplug
regression on many systems, as reported here:
https://lkml.org/lkml/2014/6/24/765
https://lkml.org/lkml/2014/7/1/473
https://lkml.org/lkml/2014/7/4/16
I didn't find this fix in mainline yet, so I thought of sending a note.
Thank you!
Regards,
Srivatsa S. Bhat
> Because of a collision with 8d056c48e486 ("CPU hotplug, smp: flush any
> pending IPI callbacks before CPU offline"), which ends up calling
> hotplug_cfd()->flush_smp_call_function_queue()->irq_work_run(), which
> is not from IRQ context.
>
> And since that already calls irq_work_run() from the hotplug path,
> remove our entire hotplug handling.
>
> Reported-by: Stephen Warren <swarren@xxxxxxxxxxxxx>
> Tested-by: Stephen Warren <swarren@xxxxxxxxxxxxx>
> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Link: http://lkml.kernel.org/n/tip-busatzs2gvz4v62258agipuf@xxxxxxxxxxxxxx
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> ---
> kernel/irq_work.c | 46 ++++------------------------------------------
> 1 file changed, 4 insertions(+), 42 deletions(-)
>
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 4b0a890..e6bcbe7 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -160,20 +160,14 @@ static void irq_work_run_list(struct llist_head *list)
> }
> }
>
> -static void __irq_work_run(void)
> -{
> - irq_work_run_list(&__get_cpu_var(raised_list));
> - irq_work_run_list(&__get_cpu_var(lazy_list));
> -}
> -
> /*
> - * Run the irq_work entries on this cpu. Requires to be ran from hardirq
> - * context with local IRQs disabled.
> + * hotplug calls this through:
> + * hotplug_cfd() -> flush_smp_call_function_queue()
> */
> void irq_work_run(void)
> {
> - BUG_ON(!in_irq());
> - __irq_work_run();
> + irq_work_run_list(&__get_cpu_var(raised_list));
> + irq_work_run_list(&__get_cpu_var(lazy_list));
> }
> EXPORT_SYMBOL_GPL(irq_work_run);
>
> @@ -189,35 +183,3 @@ void irq_work_sync(struct irq_work *work)
> cpu_relax();
> }
> EXPORT_SYMBOL_GPL(irq_work_sync);
> -
> -#ifdef CONFIG_HOTPLUG_CPU
> -static int irq_work_cpu_notify(struct notifier_block *self,
> - unsigned long action, void *hcpu)
> -{
> - long cpu = (long)hcpu;
> -
> - switch (action) {
> - case CPU_DYING:
> - /* Called from stop_machine */
> - if (WARN_ON_ONCE(cpu != smp_processor_id()))
> - break;
> - __irq_work_run();
> - break;
> - default:
> - break;
> - }
> - return NOTIFY_OK;
> -}
> -
> -static struct notifier_block cpu_notify;
> -
> -static __init int irq_work_init_cpu_notifier(void)
> -{
> - cpu_notify.notifier_call = irq_work_cpu_notify;
> - cpu_notify.priority = 0;
> - register_cpu_notifier(&cpu_notify);
> - return 0;
> -}
> -device_initcall(irq_work_init_cpu_notifier);
> -
> -#endif /* CONFIG_HOTPLUG_CPU */
>
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