Messages in this thread | | | Date | Mon, 11 Mar 2013 12:21:05 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCHv2] perf: Fix vmalloc ring buffer free function |
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heya ;)
great to hear from you again!
On Mon, Mar 11, 2013 at 10:40:43AM +0100, Peter Zijlstra wrote: > On Fri, 2013-03-01 at 17:34 +0100, Jiri Olsa wrote: > > If we allocate perf ring buffer with the size of single page,
SNIP
> > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c > > index 23cb34f..a802151 100644 > > --- a/kernel/events/ring_buffer.c > > +++ b/kernel/events/ring_buffer.c > > @@ -154,7 +154,8 @@ int perf_output_begin(struct perf_output_handle *handle, > > if (head - local_read(&rb->wakeup) > rb->watermark) > > local_add(rb->watermark, &rb->wakeup); > > > > - handle->page = offset >> (PAGE_SHIFT + page_order(rb)); > > + /* page is allways 0 for CONFIG_PERF_USE_VMALLOC option */ > > + handle->page = offset >> PAGE_SHIFT; > > I don't get that comment.. also it makes the calculation for page > inconsistent with the below calculation for addr. > > We basically want to split the offset into a page number and an offset > within that; this means we need: > > pg_nr = offset >> page_shift; > pg_offset = offset & (1 << page_shift) - 1; > > You just wrecked that. > > > handle->page &= rb->nr_pages - 1;
here's ^^^ where the handle->page becomes 0 due to (rb->nr_pages == 0)
for CONFIG_PERF_USE_VMALLOC we use only the first item in rb->data_pages[] array, which holds the whole data memory, and got accessed by 'offset' directly
> > handle->size = offset & ((PAGE_SIZE << page_order(rb)) - 1); > > handle->addr = rb->data_pages[handle->page]; > > @@ -312,11 +313,21 @@ void rb_free(struct ring_buffer *rb) > > } > > > > #else > > +/* > > + * Returns the total number of pages allocated > > + * by ring buffer including the user page. > > + */ > > +static int page_nr(struct ring_buffer *rb) > > +{ > > + return page_order(rb) == -1 ? > > + 1 : /* no data, just user page */ > > + 1 + (1 << page_order(rb)); /* user page + data pages */ > > +} > > I think a number of the bugs below is due to the conflation of data > pages vs total pages. It might be best to call this data_page_nr() and > leave the +1 for the sites where its needed.
both places using page_nr need total pages count, maybe I can rename it into total_page_nr()
> > > > struct page * > > perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff) > > { > > - if (pgoff > (1UL << page_order(rb))) > > + if (pgoff > page_nr(rb)) > > return NULL; > > This is just wrong.. you have page_nr() be 1+2^n, but the comparison is
> '>' not '>=', this means we get a range of 2+2^n, not the desired 1+2^n.
ouch, missed that one
thanks, jirka
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