linux-kernel - Re: [PATCH] mm: Restore mmput

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Date:   Thu, 14 Sep 2017 10:19:29 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Sherry Yang <sherryy@...roid.com>
Cc:     linux-kernel@...r.kernel.org, tkjos@...gle.com, maco@...gle.com,
        arve@...roid.com, gregkh@...uxfoundation.org,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Hoeun Ryu <hoeun.ryu@...il.com>,
        Christoph Lameter <cl@...ux.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] mm: Restore mmput_async

On Wed 13-09-17 17:59:27, Sherry Yang wrote:
> Restore asynchronous mmput, allowing mmput_async to be called
> from an atomic context in Android binder shrinker callback.
> 
> mmput_async was initially introduced in ec8d7c14e
> ("mm, oom_reaper: do not mmput synchronously from the
> oom reaper context"), and was removed in 212925802
> ("mm: oom: let oom_reap_task and exit_mmap run concurrently")
> 
> Signed-off-by: Sherry Yang <sherryy@...roid.com>

I would just fold this into https://lkml.org/lkml/2017/9/8/785. The
patch is simple enough to take this in one go and it will be clear who
and why needs to restore the api.

No objections otherwise.
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  include/linux/sched/mm.h |  6 ++++++
>  kernel/fork.c            | 18 ++++++++++++++++++
>  2 files changed, 24 insertions(+)
> 
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 3a19c253bdb1..ae53e413fb13 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -84,6 +84,12 @@ static inline bool mmget_not_zero(struct mm_struct *mm)
>  
>  /* mmput gets rid of the mappings and all user-space */
>  extern void mmput(struct mm_struct *);
> +#ifdef CONFIG_MMU
> +/* same as above but performs the slow path from the async context. Can
> + * be called from the atomic context as well
> + */
> +void mmput_async(struct mm_struct *);
> +#endif
>  
>  /* Grab a reference to a task's mm, if it is not already going away */
>  extern struct mm_struct *get_task_mm(struct task_struct *task);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 10646182440f..e702cb9ffbd8 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -946,6 +946,24 @@ void mmput(struct mm_struct *mm)
>  }
>  EXPORT_SYMBOL_GPL(mmput);
>  
> +#ifdef CONFIG_MMU
> +static void mmput_async_fn(struct work_struct *work)
> +{
> +	struct mm_struct *mm = container_of(work, struct mm_struct,
> +					    async_put_work);
> +
> +	__mmput(mm);
> +}
> +
> +void mmput_async(struct mm_struct *mm)
> +{
> +	if (atomic_dec_and_test(&mm->mm_users)) {
> +		INIT_WORK(&mm->async_put_work, mmput_async_fn);
> +		schedule_work(&mm->async_put_work);
> +	}
> +}
> +#endif
> +
>  /**
>   * set_mm_exe_file - change a reference to the mm's executable file
>   *
> -- 
> 2.11.0 (Apple Git-81)
> 

-- 
Michal Hocko
SUSE Labs