On Thu, Aug 19, 2021 at 09:56:45AM +0800, Boqun Feng wrote: > [Cc Thomas and Frederic since they contributed the clean-up to these > macros recently] > > Background for discussion: > > https://lore.kernel.org/lkml/20210814014234.51395-1-changbin.du@xxxxxxxxx/ > > On Thu, Aug 19, 2021 at 07:59:16AM +0800, Changbin Du wrote: > > On Tue, Aug 17, 2021 at 12:03:16AM +0800, Boqun Feng wrote: > > > On Sat, Aug 14, 2021 at 09:42:34AM +0800, Changbin Du wrote: > > > > At some places we need to determine whether we're in nmi, hardirq or > > > > softirq context. This adds a macro in_serving_irq() as a shortcut for > > > > that. > > > > > > > > Meanwhile, apply this new macro to existing code in rcutiny and vsprintf. > > > > > > > > Signed-off-by: Changbin Du <changbin.du@xxxxxxxxx> > > > > --- > > > > include/linux/preempt.h | 4 +++- > > > > include/linux/rcutiny.h | 3 +-- > > > > lib/vsprintf.c | 2 +- > > > > 3 files changed, 5 insertions(+), 4 deletions(-) > > > > > > > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h > > > > index 9881eac0698f..9a1c924e2c6c 100644 > > > > --- a/include/linux/preempt.h > > > > +++ b/include/linux/preempt.h > > > > @@ -92,12 +92,14 @@ > > > > * in_nmi() - We're in NMI context > > > > * in_hardirq() - We're in hard IRQ context > > > > * in_serving_softirq() - We're in softirq context > > > > + * in_serving_irq() - We're in nmi, hardirq or softirq context > > > > * in_task() - We're in task context > > > > */ > > > > #define in_nmi() (nmi_count()) > > > > #define in_hardirq() (hardirq_count()) > > > > #define in_serving_softirq() (softirq_count() & SOFTIRQ_OFFSET) > > > > -#define in_task() (!(in_nmi() | in_hardirq() | in_serving_softirq())) > > > > +#define in_serving_irq() (in_nmi() | in_hardirq() | in_serving_softirq()) > > > > +#define in_task() (!in_serving_irq()) > > > > > > > > > > So in_serving_irq() is !in_task(), right? If so, why not... > > > > > Adding in_serving_irq() is to reflect the real purpose so improve readability. > > And can we preserve that !in_task() means in serving irq context in future? I don't know. > > > > Sure, no one could predict the future. But if a third context (other > than thread context and {hard,soft}irq context) comes up, which I think > is highly unlikely, we could (and should) audit all callsites of > in_task() for necessary adjustment. And introducing in_serving_irq() > won't help us in that case, because we will still need to audit usage of > in_serving_irq(), for example, let's say rcu_is_idle_cpu() for RCU_TINY > is defined as > > #define rcu_is_idle_cpu(cpu) (is_idle_task(current) && !in_serving_irq()) > > and we have a new type of context, and we can use in_other() to test > whether we are in it. Now even with in_serving_irq() introduced, we > still need to make sure the correct version of rcu_is_idle_cpu() is > either > > (is_idle_task(current) && (!in_serving_irq() && !in_other())) > > or > > (is_idle_task(current) && !in_serving_irq()) > > Therefore, I don't see the point of introducing in_serving_irq(). > ok, as in_serving_irq() is only used in two places, it is not common to judge if it is in serving irq context. So this new macro doesn't help much. > Regards, > Boqun > > > -- > > Cheers, > > Changbin Du -- Cheers, Changbin Du
