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    SubjectRe: [tip:core/ipi] generic-ipi: eliminate spurious pointless WARN_ON()s
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    On Fri, 2009-03-13 at 01:39 +0000, Jan Beulich wrote:
    > Commit-ID: 6a09dfa870ba0ed21b1124539968a36b42660661
    > Gitweb: http://git.kernel.org/tip/6a09dfa870ba0ed21b1124539968a36b42660661
    > Author: Jan Beulich <jbeulich@novell.com>
    > AuthorDate: Thu, 12 Mar 2009 13:21:50 +0000
    > Commit: Ingo Molnar <mingo@elte.hu>
    > CommitDate: Fri, 13 Mar 2009 02:14:41 +0100
    >
    > generic-ipi: eliminate spurious pointless WARN_ON()s
    >
    > Namely during early boot, the panic() or BUG() paths may end up in
    > smp_call_function_*() with just a single online CPU. In that situation
    > the warnings generated are not only meaningless, but also result in
    > relevant output being cluttered.
    >
    > Therefore, defer the WARN_ON() checks until after the (unaffected from
    > the problem that is being attempted to be detected here) cases have
    > been handled.
    >
    > Signed-off-by: Jan Beulich <jbeulich@novell.com>
    > LKML-Reference: <49B91A7E.76E4.0078.0@novell.com>
    > Signed-off-by: Ingo Molnar <mingo@elte.hu>

    I don't really like this,.. it moves the WARN_ON to weird locations
    without an explanatory comment.

    Wouldn't leaving them in place but changing them to:

    WARN_ON(irqs_disabled() && system_state == SYSTEM_RUNNING);

    be clearer?

    > ---
    > kernel/smp.c | 12 ++++++------
    > 1 files changed, 6 insertions(+), 6 deletions(-)
    >
    > diff --git a/kernel/smp.c b/kernel/smp.c
    > index 7ad2262..37b90a9 100644
    > --- a/kernel/smp.c
    > +++ b/kernel/smp.c
    > @@ -284,9 +284,6 @@ 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(irqs_disabled());
    > -
    > if (cpu == this_cpu) {
    > local_irq_save(flags);
    > func(info);
    > @@ -295,6 +292,9 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
    > if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
    > struct call_single_data *data = &d;
    >
    > + /* Can deadlock when called with interrupts disabled */
    > + WARN_ON(irqs_disabled());
    > +
    > if (!wait)
    > data = &__get_cpu_var(csd_data);
    >
    > @@ -364,9 +364,6 @@ 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(irqs_disabled());
    > -
    > /* So, what's a CPU they want? Ignoring this one. */
    > cpu = cpumask_first_and(mask, cpu_online_mask);
    > if (cpu == this_cpu)
    > @@ -387,6 +384,9 @@ void smp_call_function_many(const struct cpumask *mask,
    > return;
    > }
    >
    > + /* Can deadlock when called with interrupts disabled */
    > + WARN_ON(irqs_disabled());
    > +
    > data = &__get_cpu_var(cfd_data);
    > csd_lock(&data->csd);
    >
    > --
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