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Message-ID: <20090824054026.GR25721@wotan.suse.de>
Date: Mon, 24 Aug 2009 07:40:26 +0200
From: Nick Piggin <npiggin@...e.de>
To: linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
suresh.b.siddha@...el.com, tglx@...utronix.de
Cc: linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/pat] generic-ipi: Allow cpus not yet online to call smp_call_function with irqs disabled
On Fri, Aug 21, 2009 at 11:51:50PM +0000, Suresh B wrote:
> Commit-ID: 269c861baa2fe7c114c3bc7831292758d29eb336
> Gitweb: http://git.kernel.org/tip/269c861baa2fe7c114c3bc7831292758d29eb336
> Author: Suresh Siddha <suresh.b.siddha@...el.com>
> AuthorDate: Wed, 19 Aug 2009 18:05:35 -0700
> Committer: H. Peter Anvin <hpa@...or.com>
> CommitDate: Fri, 21 Aug 2009 16:25:43 -0700
>
> generic-ipi: Allow cpus not yet online to call smp_call_function with irqs disabled
>
> Because of deadlock possiblities smp_call_function() is not allowed to
> be called with interrupts disabled. Add an exception for the cpu not
> yet online, as no one else can send smp call function interrupt to this
> cpu that is not yet online and as such deadlock condition is not possible.
>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> Acked-by: Nick Piggin <npiggin@...e.de>
> Signed-off-by: H. Peter Anvin <hpa@...or.com>
I don't know if we should allow the use of smp_call_function here --
only call_function_single. CPU hotplug code is required to set up
some call_function data and if the cpu is offline then it might not
be set up correctly.
Also, I would say that we should just restrict this to wait==1 case
because in that case the stack can trivially be used for data. In
the wait==0 case, it is more complex. In the current implementation
it should be OK (it uses per-cpu data), but we've used kmalloc
there in the past, which probably wouldn't work either.
> ---
> kernel/smp.c | 40 ++++++++++++++++++++++++++++++++++------
> 1 files changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index ad63d85..2accdf6 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -177,6 +177,11 @@ void generic_smp_call_function_interrupt(void)
> int cpu = get_cpu();
>
> /*
> + * Shouldn't receive this interrupt on a cpu that is not yet online.
> + */
> + WARN_ON_ONCE(!cpu_online(cpu));
> +
> + /*
> * Ensure entry is visible on call_function_queue after we have
> * entered the IPI. See comment in smp_call_function_many.
> * If we don't have this, then we may miss an entry on the list
> @@ -230,6 +235,11 @@ void generic_smp_call_function_single_interrupt(void)
> unsigned int data_flags;
> LIST_HEAD(list);
>
> + /*
> + * Shouldn't receive this interrupt on a cpu that is not yet online.
> + */
> + WARN_ON_ONCE(!cpu_online(smp_processor_id()));
> +
> spin_lock(&q->lock);
> list_replace_init(&q->list, &list);
> spin_unlock(&q->lock);
> @@ -285,8 +295,14 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
> */
> this_cpu = get_cpu();
>
> - /* Can deadlock when called with interrupts disabled */
> - WARN_ON_ONCE(irqs_disabled() && !oops_in_progress);
> + /*
> + * Can deadlock when called with interrupts disabled.
> + * We allow cpu's that are not yet online though, as no one else can
> + * send smp call function interrupt to this cpu and as such deadlocks
> + * can't happen.
> + */
> + WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
> + && !oops_in_progress);
>
> if (cpu == this_cpu) {
> local_irq_save(flags);
> @@ -329,8 +345,14 @@ void __smp_call_function_single(int cpu, struct call_single_data *data,
> {
> csd_lock(data);
>
> - /* Can deadlock when called with interrupts disabled */
> - WARN_ON_ONCE(wait && irqs_disabled() && !oops_in_progress);
> + /*
> + * Can deadlock when called with interrupts disabled.
> + * We allow cpu's that are not yet online though, as no one else can
> + * send smp call function interrupt to this cpu and as such deadlocks
> + * can't happen.
> + */
> + WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
> + && !oops_in_progress);
>
> generic_exec_single(cpu, data, wait);
> }
> @@ -365,8 +387,14 @@ void smp_call_function_many(const struct cpumask *mask,
> unsigned long flags;
> int cpu, next_cpu, this_cpu = smp_processor_id();
>
> - /* Can deadlock when called with interrupts disabled */
> - WARN_ON_ONCE(irqs_disabled() && !oops_in_progress);
> + /*
> + * Can deadlock when called with interrupts disabled.
> + * We allow cpu's that are not yet online though, as no one else can
> + * send smp call function interrupt to this cpu and as such deadlocks
> + * can't happen.
> + */
> + WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
> + && !oops_in_progress);
>
> /* So, what's a CPU they want? Ignoring this one. */
> cpu = cpumask_first_and(mask, cpu_online_mask);
--
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