Re: [PATCH v6 17/18] mm/memory-failure: increase queued recovery work's priority

[Borislav Petkov <bp@alien8.de>]

+ Peter.

On Fri, Sep 21, 2018 at 11:17:04PM +0100, James Morse wrote:
> arm64 can take an NMI-like error notification when user-space steps in
> some corrupt memory. APEI's GHES code will call memory_failure_queue()
> to schedule the recovery work. We then return to user-space, possibly
> taking the fault again.
> 
> Currently the arch code unconditionally signals user-space from this
> path, so we don't get stuck in this loop, but the affected process
> never benefits from memory_failure()s recovery work. To fix this we
> need to know the recovery work will run before we get back to user-space.
> 
> Increase the priority of the recovery work by scheduling it on the
> system_highpri_wq, then try to bump the current task off this CPU
> so that the recovery work starts immediately.
> 
> Reported-by: Xie XiuQi <xiexiuqi@huawei.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Reviewed-by: Punit Agrawal <punit.agrawal@arm.com>
> Tested-by: Tyler Baicar <tbaicar@codeaurora.org>
> Tested-by: gengdongjiu <gengdongjiu@huawei.com>
> CC: Xie XiuQi <xiexiuqi@huawei.com>
> CC: gengdongjiu <gengdongjiu@huawei.com>
> ---
>  mm/memory-failure.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 0cd3de3550f0..4e7b115cea5a 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -56,6 +56,7 @@
>  #include <linux/memory_hotplug.h>
>  #include <linux/mm_inline.h>
>  #include <linux/memremap.h>
> +#include <linux/preempt.h>
>  #include <linux/kfifo.h>
>  #include <linux/ratelimit.h>
>  #include <linux/page-isolation.h>
> @@ -1454,6 +1455,7 @@ static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);
>   */
>  void memory_failure_queue(unsigned long pfn, int flags)
>  {
> +	int cpu = smp_processor_id();
>  	struct memory_failure_cpu *mf_cpu;
>  	unsigned long proc_flags;
>  	struct memory_failure_entry entry = {
> @@ -1463,11 +1465,14 @@ void memory_failure_queue(unsigned long pfn, int flags)
>  
>  	mf_cpu = &get_cpu_var(memory_failure_cpu);
>  	spin_lock_irqsave(&mf_cpu->lock, proc_flags);
> -	if (kfifo_put(&mf_cpu->fifo, entry))
> -		schedule_work_on(smp_processor_id(), &mf_cpu->work);
> -	else
> +	if (kfifo_put(&mf_cpu->fifo, entry)) {
> +		queue_work_on(cpu, system_highpri_wq, &mf_cpu->work);
> +		set_tsk_need_resched(current);
> +		preempt_set_need_resched();

What guarantees the workqueue would run before the process? I see this:

``WQ_HIGHPRI``
  Work items of a highpri wq are queued to the highpri
  worker-pool of the target cpu.  Highpri worker-pools are
  served by worker threads with elevated nice level.

but is that enough?

-- 
Regards/Gruss,
    Boris.

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