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Subject[PATCH 4.19 54/85] perf/core: Fix impossible ring-buffer sizes warning
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ingo Molnar <mingo@kernel.org>

commit 528871b456026e6127d95b1b2bd8e3a003dc1614 upstream.

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>
Fixes: 9dff0aa95a32 ("perf/core: Don't WARN() for impossible ring-buffer sizes")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/events/ring_buffer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -724,7 +724,7 @@ struct ring_buffer *rb_alloc(int nr_page
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);

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