Re: [PATCH v2 1/3] mm/memory-failure: Add memory_failure_queue_kick()

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Friday, May 1, 2020 6:45:41 PM CEST James Morse wrote:
> The GHES code calls memory_failure_queue() from IRQ context to schedule
> work on the current CPU so that memory_failure() can sleep.
> 
> For synchronous memory errors the arch code needs to know any signals
> that memory_failure() will trigger are pending before it returns to
> user-space, possibly when exiting from the IRQ.
> 
> Add a helper to kick the memory failure queue, to ensure the scheduled
> work has happened. This has to be called from process context, so may
> have been migrated from the original cpu. Pass the cpu the work was
> queued on.
> 
> Change memory_failure_work_func() to permit being called on the 'wrong'
> cpu.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> Tested-by: Tyler Baicar <baicar@os.amperecomputing.com>
> ---
>  include/linux/mm.h  |  1 +
>  mm/memory-failure.c | 15 ++++++++++++++-
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5a323422d783..c606dbbfa5e1 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3012,6 +3012,7 @@ enum mf_flags {
>  };
>  extern int memory_failure(unsigned long pfn, int flags);
>  extern void memory_failure_queue(unsigned long pfn, int flags);
> +extern void memory_failure_queue_kick(int cpu);
>  extern int unpoison_memory(unsigned long pfn);
>  extern int get_hwpoison_page(struct page *page);
>  #define put_hwpoison_page(page)	put_page(page)
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index a96364be8ab4..c4afb407bf0f 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1493,7 +1493,7 @@ static void memory_failure_work_func(struct work_struct *work)
>  	unsigned long proc_flags;
>  	int gotten;
>  
> -	mf_cpu = this_cpu_ptr(&memory_failure_cpu);
> +	mf_cpu = container_of(work, struct memory_failure_cpu, work);
>  	for (;;) {
>  		spin_lock_irqsave(&mf_cpu->lock, proc_flags);
>  		gotten = kfifo_get(&mf_cpu->fifo, &entry);
> @@ -1507,6 +1507,19 @@ static void memory_failure_work_func(struct work_struct *work)
>  	}
>  }
>  
> +/*
> + * Process memory_failure work queued on the specified CPU.
> + * Used to avoid return-to-userspace racing with the memory_failure workqueue.
> + */
> +void memory_failure_queue_kick(int cpu)
> +{
> +	struct memory_failure_cpu *mf_cpu;
> +
> +	mf_cpu = &per_cpu(memory_failure_cpu, cpu);
> +	cancel_work_sync(&mf_cpu->work);
> +	memory_failure_work_func(&mf_cpu->work);
> +}
> +
>  static int __init memory_failure_init(void)
>  {
>  	struct memory_failure_cpu *mf_cpu;
> 

I could apply this provided an ACK from the mm people.

Thanks!