linux-kernel - Re: [PATCH v2 5/7] perf: Introduce address range filtering

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Date:	Thu, 28 Apr 2016 19:09:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org, vince@...ter.net, eranian@...gle.com,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH v2 5/7] perf: Introduce address range filtering

On Wed, Apr 27, 2016 at 06:44:46PM +0300, Alexander Shishkin wrote:
> +/*
> + * In order to contain the amount of racy and tricky in the address filter
> + * configuration management, it is a two part process:
> + *
> + * (p1) when userspace mappings change as a result of (1) or (2) or (3) below,
> + *      we update the addresses of corresponding vmas in
> + *	event::addr_filters_offs array and bump the event::addr_filters_gen;
> + * (p2) when an event is scheduled in (pmu::add), it calls
> + *      perf_event_addr_filters_sync() which calls pmu::addr_filters_sync()
> + *      if the generation has changed since the previous call.
> + *
> + * If (p1) happens while the event is active, we restart it to force (p2).

Tiny nit; restart only does ::stop(),::start(), which doesn't go through
::add().

> + *
> + * (1) perf_addr_filters_apply(): adjusting filters' offsets based on
> + *     pre-existing mappings, called once when new filters arrive via SET_FILTER
> + *     ioctl;
> + * (2) perf_addr_filters_adjust(): adjusting filters' offsets based on newly
> + *     registered mapping, called for every new mmap(), with mm::mmap_sem down
> + *     for reading;
> + * (3) perf_event_addr_filters_exec(): clearing filters' offsets in the process
> + *     of exec.
> + */

> +static unsigned long perf_addr_filter_apply(struct perf_addr_filter *filter,
> +					    struct mm_struct *mm)
> +{
> +	struct vm_area_struct *vma;
> +
> +	for (vma = mm->mmap; vma->vm_next; vma = vma->vm_next) {

Doesn't this miss the very last vma? That is, I was expecting:

	for (vma = mm->mmap; vma; vma = vma->vm_next) {

> +		struct file *file = vma->vm_file;
> +		unsigned long off = vma->vm_pgoff << PAGE_SHIFT;
> +		unsigned long vma_size = vma->vm_end - vma->vm_start;
> +
> +		if (!file)
> +			continue;
> +
> +		if (!perf_addr_filter_match(filter, file, off, vma_size))
> +			continue;
> +
> +		return vma->vm_start;
> +	}
> +
> +	return 0;
> +}