Re: [PATCH 4.14 198/205] perf/core: Dont WARN() for impossible ring-buffer sizes

Rantala, Tommi T. (Nokia - FI/Espoo)
2019-02-13T13:03:48Z

On Mon, 2019-02-11 at 15:19 +0100, Greg Kroah-Hartman wrote:
> 4.14-stable review patch. If anyone has any objections, please let
> me know.
>
> ------------------
>
> From: Mark Rutland <mark.rutland@arm.com>
>
> commit 9dff0aa95a324e262ffb03f425d00e4751f3294e upstream.
>
> The perf tool uses /proc/sys/kernel/perf_event_mlock_kb to determine
> how
> large its ringbuffer mmap should be. This can be configured to
> arbitrary
> values, which can be larger than the maximum possible allocation from
> kmalloc.
>
> When this is configured to a suitably large value (e.g. thanks to the
> perf fuzzer), attempting to use perf record triggers a WARN_ON_ONCE()
> in
> __alloc_pages_nodemask():
>
> WARNING: CPU: 2 PID: 5666 at mm/page_alloc.c:4511
> __alloc_pages_nodemask+0x3f8/0xbc8
>
> Let's avoid this by checking that the requested allocation is
> possible
> before calling kzalloc.

Hi,

Perf tool is broken for me in 4.14.99 (running in x86_64 VM), bisection
points to this patch.

# perf top
Error:
Failed to mmap with 12 (Cannot allocate memory)

# perf trace
Cannot allocate memory

# strace -T -tt -f -y perf top
[...]
14:22:09.829544 openat(AT_FDCWD,
"/proc/sys/kernel/perf_event_mlock_kb", O_RDONLY) =
18</proc/sys/kernel/perf_event_mlock_kb> <0.000015>
14:22:09.829612 read(18</proc/sys/kernel/perf_event_mlock_kb>, "516\n",
64) = 4 <0.000011>
14:22:09.829655 close(18</proc/sys/kernel/perf_event_mlock_kb>) = 0
<0.000008>
14:22:09.829702 mmap(NULL, 528384, PROT_READ|PROT_WRITE, MAP_SHARED,
3<anon_inode:[perf_event]>, 0) = -1 ENOMEM (Cannot allocate memory)
<0.000015>
14:22:09.829763 write(2</dev/pts/0>, "Error:\n", 7) = 7 <0.000009>
14:22:09.829810 write(2</dev/pts/0>, "Failed to mmap with 12 (Cannot
a"..., 48) = 48 <0.000008>

Changing the patch like this fixes it...

- if (order_base_2(size) >= MAX_ORDER)
+ if (order_base_2(size) > MAX_ORDER)

-Tommi

> Reported-by: Julien Thierry <julien.thierry@arm.com>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Julien Thierry <julien.thierry@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: <stable@vger.kernel.org>
> Link:
> https://lkml.kernel.org/r/20190110142745.25495-1-mark.rutland@arm.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> kernel/events/ring_buffer.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -719,6 +719,9 @@ 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)
> + goto fail;
> +
> rb = kzalloc(size, GFP_KERNEL);
> if (!rb)
> goto fail;
>
>