Re: [PATCH v2 wq/for-6.9] workqueue, irq_work: Build fix for !CONFIG_IRQ_WORK

[Anders Roxell]

On Fri, 16 Feb 2024 at 06:10, Tejun Heo <tj@xxxxxxxxxx> wrote:
>
> 2f34d7337d98 ("workqueue: Fix queue_work_on() with BH workqueues") added
> irq_work usage to workqueue; however, it turns out irq_work is actually
> optional and the change breaks build on configuration which doesn't have
> CONFIG_IRQ_WORK enabled.
>
> Fix build by making workqueue use irq_work only when CONFIG_SMP and enabling
> CONFIG_IRQ_WORK when CONFIG_SMP is set. It's reasonable to argue that it may
> be better to just always enable it. However, this still saves a small bit of
> memory for tiny UP configs and also the least amount of change, so, for now,
> let's keep it conditional.
>
> Verified to do the right thing for x86_64 allnoconfig and defconfig, and
> aarch64 allnoconfig, allnoconfig + prink disable (SMP but nothing selects
> IRQ_WORK) and a modified aarch64 Kconfig where !SMP and nothing selects
> IRQ_WORK.
>
> v2: `depends on SMP` leads to Kconfig warnings when CONFIG_IRQ_WORK is
>     selected by something else when !CONFIG_SMP. Use `def_bool y if SMP`
>     instead.
>
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
> Fixes: 2f34d7337d98 ("workqueue: Fix queue_work_on() with BH workqueues")
> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> ---
> Hello,
>
> Unfortunately, the previous patch triggers Kconfig warnings when IRQ_WORK is
> selected by something else but !CONFIG_SMP. This one seems to do the right
> thing in all cases.
>
> Naresh, Anders, can you please test it again?

I applied this patch on yesterdays next tag next-20240215 and I was able to
build the arm64 tinyconfig.

Tested-by: Anders Roxell <anders.roxell@xxxxxxxxxx>

>
> Thanks.
>
>  init/Kconfig       |  2 +-
>  kernel/workqueue.c | 24 +++++++++++++++---------
>  2 files changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 8df18f3a9748..0d21c9e0398f 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -106,7 +106,7 @@ config CONSTRUCTORS
>         bool
>
>  config IRQ_WORK
> -       bool
> +       def_bool y if SMP
>
>  config BUILDTIME_TABLE_SORT
>         bool
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 04e35dbe6799..6ae441e13804 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1209,6 +1209,20 @@ static struct irq_work *bh_pool_irq_work(struct worker_pool *pool)
>         return &per_cpu(bh_pool_irq_works, pool->cpu)[high];
>  }
>
> +static void kick_bh_pool(struct worker_pool *pool)
> +{
> +#ifdef CONFIG_SMP
> +       if (unlikely(pool->cpu != smp_processor_id())) {
> +               irq_work_queue_on(bh_pool_irq_work(pool), pool->cpu);
> +               return;
> +       }
> +#endif
> +       if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
> +               raise_softirq_irqoff(HI_SOFTIRQ);
> +       else
> +               raise_softirq_irqoff(TASKLET_SOFTIRQ);
> +}
> +
>  /**
>   * kick_pool - wake up an idle worker if necessary
>   * @pool: pool to kick
> @@ -1227,15 +1241,7 @@ static bool kick_pool(struct worker_pool *pool)
>                 return false;
>
>         if (pool->flags & POOL_BH) {
> -               if (likely(pool->cpu == smp_processor_id())) {
> -                       if (pool->attrs->nice == HIGHPRI_NICE_LEVEL)
> -                               raise_softirq_irqoff(HI_SOFTIRQ);
> -                       else
> -                               raise_softirq_irqoff(TASKLET_SOFTIRQ);
> -               } else {
> -                       irq_work_queue_on(bh_pool_irq_work(pool), pool->cpu);
> -               }
> -
> +               kick_bh_pool(pool);
>                 return true;
>         }
>
> --
> 2.43.2
>