linux-kernel - Re: [PATCH 1/2] perf: Add munmap callback

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Message-ID: <20181025002943.GT3109@worktop.c.hoisthospitality.com>
Date:   Thu, 25 Oct 2018 02:29:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     tglx@...utronix.de, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, bp@...en8.de, ak@...ux.intel.com,
        eranian@...gle.com
Subject: Re: [PATCH 1/2] perf: Add munmap callback

On Wed, Oct 24, 2018 at 08:11:15AM -0700, kan.liang@...ux.intel.com wrote:
> +void perf_event_munmap(void)
> +{
> +	struct perf_cpu_context *cpuctx;
> +	unsigned long flags;
> +	struct pmu *pmu;
> +
> +	local_irq_save(flags);

It is impossible to get here with IRQs already disabled.

> +	list_for_each_entry(cpuctx, this_cpu_ptr(&sched_cb_list), sched_cb_entry) {
> +		pmu = cpuctx->ctx.pmu;
> +
> +		if (!pmu->munmap)
> +			continue;
> +
> +		perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> +		perf_pmu_disable(pmu);
> +
> +		pmu->munmap();
> +
> +		perf_pmu_enable(pmu);
> +
> +		perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
> +	}
> +	local_irq_restore(flags);
> +}
> +
>  static void perf_event_switch(struct task_struct *task,
>  			      struct task_struct *next_prev, bool sched_in);
>  
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 5f2b2b184c60..61978ad8c480 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2777,6 +2777,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
>  	/*
>  	 * Remove the vma's, and unmap the actual pages
>  	 */
> +	perf_event_munmap();

I think that if you add the munmap hook, you should do it right and at
least do it such that we can solve the other munmap problem.

>  	detach_vmas_to_be_unmapped(mm, vma, prev, end);
>  	unmap_region(mm, vma, prev, start, end);
>  
> -- 
> 2.17.1
>