linux-kernel - [PATCH 3.16 153/202] perf/core: Fix impossible ring-buffer sizes warning

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Message-ID: <lsq.1556377989.339927743@decadent.org.uk>
Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Jiri Olsa" <jolsa@...hat.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Namhyung Kim" <namhyung@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Alexander Shishkin" <alexander.shishkin@...ux.intel.com>,
        "Ingo Molnar" <mingo@...nel.org>,
        "Jin, Yao" <yao.jin@...ux.intel.com>,
        "Arnaldo Carvalho de Melo" <acme@...hat.com>,
        "Julien Thierry" <julien.thierry@....com>,
        "Mark Rutland" <mark.rutland@....com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 153/202] perf/core: Fix impossible ring-buffer sizes
 warning

3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Ingo Molnar <mingo@...nel.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@...ux.intel.com>
Bisected-by: Borislav Petkov <bp@...en8.de>
Analyzed-by: Peter Zijlstra <peterz@...radead.org>
Cc: Julien Thierry <julien.thierry@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Fixes: 9dff0aa95a32 ("perf/core: Don't WARN() for impossible ring-buffer sizes")
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -282,7 +282,7 @@ 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);