Re: [PATCH] mm/swap.c: workaround for_each_cpu() bug on UP kernel.

[Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>]

Andrew, please replace

  mm-swapc-workaround-for_each_cpu-bug-on-up-kernel.patch

with Michal's patch.

(I didn't debug this. Guenter already debugged this before reporting.)

On 2019/02/12 20:29, Michal Hocko wrote:
>>From db104f132bd6e1c02ecbe65e62c12caa7e4e2e2a Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Tue, 12 Feb 2019 12:25:28 +0100
> Subject: [PATCH] mm: handle lru_add_drain_all for UP properly
> 
> Since for_each_cpu(cpu, mask) added by commit 2d3854a37e8b767a ("cpumask:
> introduce new API, without changing anything") did not evaluate the mask
> argument if NR_CPUS == 1 due to CONFIG_SMP=n, lru_add_drain_all() is
> hitting WARN_ON() at __flush_work() added by commit 4d43d395fed12463
> ("workqueue: Try to catch flush_work() without INIT_WORK().")
> by unconditionally calling flush_work() [1].
> 
> Workaround this issue by using CONFIG_SMP=n specific lru_add_drain_all
> implementation. There is no real need to defer the implementation to the
> workqueue as the draining is going to happen on the local cpu. So alias
> lru_add_drain_all to lru_add_drain which does all the necessary work.
> 
> [1] https://lkml.kernel.org/r/18a30387-6aa5-6123-e67c-57579ecc3f38@roeck-us.net
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Debugged-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  mm/swap.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/mm/swap.c b/mm/swap.c
> index 4929bc1be60e..88a6021fce11 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -660,6 +660,7 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)
>  
>  static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
>  
> +#ifdef CONFIG_SMP
>  /*
>   * Doesn't need any cpu hotplug locking because we do rely on per-cpu
>   * kworkers being shut down before our page_alloc_cpu_dead callback is
> @@ -702,6 +703,10 @@ void lru_add_drain_all(void)
>  
>  	mutex_unlock(&lock);
>  }
> +#else
> +#define lru_add_drain_all() lru_add_drain()
> +
> +#endif
>  
>  /**
>   * release_pages - batched put_page()
>