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

Peter Zijlstra
2016-04-28T17:09:22Z

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;
> +}