On 12/06/2023 06:24, Shuai Xue wrote:
> When perf-record with a large AUX area, e.g 2GB:
>
> #perf record -C 0 -m ,2G -e arm_spe_0// -- sleep 1
>
> it reveals a WARNING with __alloc_pages:
>
> [ 48.888553] ------------[ cut here ]------------
> [ 48.888559] WARNING: CPU: 39 PID: 17438 at mm/page_alloc.c:5568 __alloc_pages+0x1ec/0x248
> [ 48.888569] Modules linked in: ip6table_filter(E) ip6_tables(E) iptable_filter(E) ebtable_nat(E) ebtables(E) vfat(E) fat(E) aes_ce_blk(E) aes_ce_cipher(E) crct10dif_ce(E) ghash_ce(E) sm4_ce_cipher(E) sm4(E) sha2_ce(E) sha256_arm64(E) sha1_ce(E) acpi_ipmi(E) sbsa_gwdt(E) sg(E) ipmi_si(E) ipmi_devintf(E) ipmi_msghandler(E) ip_tables(E) sd_mod(E) ast(E) drm_kms_helper(E) syscopyarea(E) sysfillrect(E) nvme(E) sysimgblt(E) i2c_algo_bit(E) nvme_core(E) drm_shmem_helper(E) ahci(E) t10_pi(E) libahci(E) drm(E) crc64_rocksoft(E) i40e(E) crc64(E) libata(E) i2c_core(E)
> [ 48.888610] CPU: 39 PID: 17438 Comm: perf Kdump: loaded Tainted: G E 6.3.0-rc4+ #56
> [ 48.888613] Hardware name: Default Default/Default, BIOS 1.2.M1.AL.P.139.00 03/22/2023
> [ 48.888614] pstate: 23400009 (nzCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
> [ 48.888616] pc : __alloc_pages+0x1ec/0x248
> [ 48.888619] lr : rb_alloc_aux_page+0x78/0xe0
> [ 48.888622] sp : ffff800037c5b9e0
> [ 48.888623] pmr_save: 000000e0
> [ 48.888624] x29: ffff800037c5b9e0 x28: ffff00082743b800 x27: 0000000000000000
> [ 48.888627] x26: 0000000000080000 x25: ffff000000000000 x24: ffff000860b21380
> [ 48.888629] x23: ffff8000093fd3c0 x22: ffff00081a4a2080 x21: 000000000000000b
> [ 48.888631] x20: 0000000000000000 x19: 000000000000000b x18: 0000000000000020
> [ 48.888634] x17: 0000000000000000 x16: ffff800008f05be8 x15: ffff00081a4a2610
> [ 48.888636] x14: 0000000000000000 x13: 323173656761705f x12: ffff00477fffeb90
> [ 48.888638] x11: 0000000000000000 x10: 0000000000000000 x9 : ffff8000083608a0
> [ 48.888641] x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000040
> [ 48.888643] x5 : 000000000007f400 x4 : 0000000000000000 x3 : 0000000000000000
> [ 48.888645] x2 : 0000000000000000 x1 : 0000000000000001 x0 : 0000000000012dc0
> [ 48.888648] Call trace:
> [ 48.888650] __alloc_pages+0x1ec/0x248
> [ 48.888653] rb_alloc_aux_page+0x78/0xe0
> [ 48.888654] rb_alloc_aux+0x13c/0x298
> [ 48.888656] perf_mmap+0x468/0x688
> [ 48.888659] mmap_region+0x308/0x8a8
> [ 48.888662] do_mmap+0x3c0/0x528
> [ 48.888664] vm_mmap_pgoff+0xf4/0x1b8
> [ 48.888666] ksys_mmap_pgoff+0x18c/0x218
> [ 48.888668] __arm64_sys_mmap+0x38/0x58
> [ 48.888671] invoke_syscall+0x50/0x128
> [ 48.888673] el0_svc_common.constprop.0+0x58/0x188
> [ 48.888674] do_el0_svc+0x34/0x50
> [ 48.888676] el0_svc+0x34/0x108
> [ 48.888679] el0t_64_sync_handler+0xb8/0xc0
> [ 48.888681] el0t_64_sync+0x1a4/0x1a8
> [ 48.888686] ---[ end trace 0000000000000000 ]---
>
> The problem is that the high-order pages for AUX area is allocated with
> an order of MAX_ORDER. Obviously, this is a bogus.
>
> Fix it with an order of MAX_ORDER - 1 at maximum.
>
> Fixes: 0a4e38e64f5e ("perf: Support high-order allocations for AUX space")
> Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
> ---
> kernel/events/ring_buffer.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 273a0fe..d6bbdb7 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -609,8 +609,8 @@ static struct page *rb_alloc_aux_page(int node, int order)
> {
> struct page *page;
>
> - if (order > MAX_ORDER)
> - order = MAX_ORDER;
> + if (order >= MAX_ORDER)
> + order = MAX_ORDER - 1;
>
> do {
> page = alloc_pages_node(node, PERF_AUX_GFP, order);
It seems like this was only just recently changed with this as the
commit message (23baf83):
mm, treewide: redefine MAX_ORDER sanely
MAX_ORDER currently defined as number of orders page allocator
supports: user can ask buddy allocator for page order between 0 and
MAX_ORDER-1.
This definition is counter-intuitive and lead to number of bugs all
over the kernel.
Change the definition of MAX_ORDER to be inclusive: the range of
orders user can ask from buddy allocator is 0..MAX_ORDER now.
It might be worth referring to this in the commit message or adding a
fixes: reference. Or maybe this new change isn't quite right?
James
