linux-kernel - [PATCH 18/20] Revert "perf: Remove the extra validity check on nr

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Date:	Tue,  3 Mar 2015 00:26:07 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Kan Liang <kan.liang@...el.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Kaixu Xia <xiakaixu@...wei.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 18/20] Revert "perf: Remove the extra validity check on nr_pages"

From: Kan Liang <kan.liang@...el.com>

This reverts commit 74390aa55678 ("perf: Remove the extra validity check
on nr_pages")

nr_pages equals to number of pages - 1 in perf_mmap. So nr_pages = 0 is
valid.

So the nr_pages != 0 && !is_power_of_2(nr_pages) are all
needed for checking. Otherwise, for example, perf test 6 failed.

 # perf test 6
  6: x86 rdpmc test                                         :Error:
 mmap() syscall returned with (Invalid argument)
 FAILED!

Signed-off-by: Kan Liang <kan.liang@...el.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Kaixu Xia <xiakaixu@...wei.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/1425280466-7830-1-git-send-email-kan.liang@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 kernel/events/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index af924bc38121..8bb20cc39a92 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4446,7 +4446,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
 	 * If we have rb pages ensure they're a power-of-two number, so we
 	 * can do bitmasks instead of modulo.
 	 */
-	if (!is_power_of_2(nr_pages))
+	if (nr_pages != 0 && !is_power_of_2(nr_pages))
 		return -EINVAL;
 
 	if (vma_size != PAGE_SIZE * (1 + nr_pages))
-- 
1.9.3

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