linux-kernel - Re: [PATCHv3] perf: Fix vmalloc ring buffer free function

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Message-ID: <1363105490.24558.12.camel@laptop>
Date:	Tue, 12 Mar 2013 17:24:50 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCHv3] perf: Fix vmalloc ring buffer free function

Right you are..

How about something like the below; using that 0 << -1 is still 0.

---
 kernel/events/ring_buffer.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 23cb34f..e72ca70 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -316,7 +316,7 @@ void rb_free(struct ring_buffer *rb)
 struct page *
 perf_mmap_to_page(struct ring_buffer *rb, unsigned long pgoff)
 {
-	if (pgoff > (1UL << page_order(rb)))
+	if (pgoff > (rb->nr_pages << page_order(rb)))
 		return NULL;
 
 	return vmalloc_to_page((void *)rb->user_page + pgoff * PAGE_SIZE);
@@ -336,10 +336,10 @@ static void rb_free_work(struct work_struct *work)
 	int i, nr;
 
 	rb = container_of(work, struct ring_buffer, work);
-	nr = 1 << page_order(rb);
+	nr = rb->nr_pages << page_order(rb);
 
 	base = rb->user_page;
-	for (i = 0; i < nr + 1; i++)
+	for (i = 0; i <= nr; i++)
 		perf_mmap_unmark_page(base + (i * PAGE_SIZE));
 
 	vfree(base);
@@ -373,7 +373,7 @@ struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
 	rb->user_page = all_buf;
 	rb->data_pages[0] = all_buf + PAGE_SIZE;
 	rb->page_order = ilog2(nr_pages);
-	rb->nr_pages = 1;
+	rb->nr_pages = !!nr_pages;
 
 	ring_buffer_init(rb, watermark, flags);
 


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