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SubjectRe: [RFC PATCH 08/15] smp: Don't warn if irq are disabled but we don't wait for the ipi
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On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote:
> The comment in smp_call_function_single() says it wants the irqs
> to be enabled otherwise it may deadlock.
>
> I can't find the reason for that though, except if we had to wait
> for a self triggered IPI but we execute the local IPI by just
> calling the function in place.
>
> In doubt, only suppress the warning if we are not waiting for the
> IPI to complete as it should really not raise any deadlock.
>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Anton Blanchard <anton@au1.ibm.com>
> Cc: Tim Pepper <lnxninja@linux.vnet.ibm.com>
> ---
> kernel/smp.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 12ed8b0..886a406 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -289,7 +289,7 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
> * send smp call function interrupt to this cpu and as such deadlocks
> * can't happen.
> */
> - WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
> + WARN_ON_ONCE(cpu_online(this_cpu) && wait && irqs_disabled()
> && !oops_in_progress);
>
> if (cpu == this_cpu) {

You just deadlocked the machine.. note how you can still wait on the
previous csd in csd_lock().


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