[BUG] WARNING in __alloc_frozen_pages_noprof

[Xianying Wang]

Hi,

I hit the following warning in the page allocator when opening a perf
event with callchain sampling after increasing
kernel.perf_event_max_stack.This warning can be triggered by first
writing a large value into kernel.perf_event_max_stack and then
opening a perf event with callchain sampling enabled.

The reproducer does two things:

1) It writes a large (but still accepted) value to the sysctl:

echo 0x40132 > /proc/sys/kernel/perf_event_max_stack

(0x40132 = 262450 in decimal. This is below the current upper bound

enforced by perf_event_max_stack_handler(), which uses 640 * 1024

as extra2.)

2) It calls perf_event_open() with callchain sampling:

struct perf_event_attr attr = {

.type = PERF_TYPE_HARDWARE,

.size = sizeof(attr),

.config = PERF_COUNT_HW_CPU_CYCLES,

.sample_type = PERF_SAMPLE_CALLCHAIN,

.sample_period = 1,

.disabled = 1,

};

fd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, 0);

The same warning is reproducible on both v6.17.0 and v6.18-rc2
(6.18.0-rc2-00120 g6fab32bb6508), only the line numbers in
__alloc_frozen_pages_noprof() differ slightly.

The suspected cause is that alloc_callchain_buffers() uses
sysctl_perf_event_max_stack directly when computing the size of the
per-CPU callchain buffers. For large but valid values of
kernel.perf_event_max_stack, perf_callchain_entry__sizeof() grows to
several megabytes, and alloc_callchain_buffers() ends up doing a very
large contiguous kmalloc_node() per CPU. This high-order allocation
then triggers the warning in __alloc_frozen_pages_noprof() in the page
allocator.

This can be reproduced on:

HEAD commit:

e5f0a698b34ed76002dc5cff3804a61c80233a7a

6fab32bb6508abbb8b7b1c5498e44f0c32320ed5

report: https://pastebin.com/raw/bCq3d4KR

console output : https://pastebin.com/raw/5hfk57Vd

kernel config : https://pastebin.com/raw/1grwrT16

C reproducer :https://pastebin.com/raw/GADWbwKN

Let me know if you need more details or testing.

Best regards,

Xianying