[tip:perf/urgent] perf/core: Fix impossible ring-buffer sizes warning

[tip-bot for Ingo Molnar <tipbot@zytor.com>]

Commit-ID:  528467ac19b279c06a55f3da99a24ebcb6e2adb1
Gitweb:     https://git.kernel.org/tip/528467ac19b279c06a55f3da99a24ebcb6e2adb1
Author:     Ingo Molnar <mingo@kernel.org>
AuthorDate: Wed, 13 Feb 2019 07:57:02 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 13 Feb 2019 08:03:55 +0100

perf/core: Fix impossible ring-buffer sizes warning

The following commit:

  9dff0aa95a32 ("perf/core: Don't WARN() for impossible ring-buffer sizes")

results in perf recording failures with larger mmap areas:

  root@skl:/tmp# perf record -g -a
  failed to mmap with 12 (Cannot allocate memory)

The root cause is that the following condition is buggy:

	if (order_base_2(size) >= MAX_ORDER)
		goto fail;

The problem is that @size is in bytes and MAX_ORDER is in pages,
so the right test is:

	if (order_base_2(size) >= PAGE_SHIFT+MAX_ORDER)
		goto fail;

Fix it.

Reported-by: "Jin, Yao" <yao.jin@linux.intel.com>
Bisected-by: Borislav Petkov <bp@alien8.de>
Analyzed-by: Peter Zijlstra <peterz@infradead.org>
Cc: Julien Thierry <julien.thierry@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/events/ring_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 309ef5a64af5..5ab4fe3b1dcc 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -734,7 +734,7 @@ struct ring_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
 	size = sizeof(struct ring_buffer);
 	size += nr_pages * sizeof(void *);
 
-	if (order_base_2(size) >= MAX_ORDER)
+	if (order_base_2(size) >= PAGE_SHIFT+MAX_ORDER)
 		goto fail;
 
 	rb = kzalloc(size, GFP_KERNEL);