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Message-ID: <751cb217-4be0-ddfc-780b-87517a8e337a@arm.com>
Date:   Mon, 12 Jun 2023 09:45:38 +0100
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Subject: Re: [PATCH 2/2] perf/ring_buffer: Fix high-order allocations for AUX
 space with correct MAX_ORDER limit
Content-Language: en-US
To:     Shuai Xue <xueshuai@linux.alibaba.com>,
        alexander.shishkin@linux.intel.com, peterz@infradead.org,
        kirill@shutemov.name
Cc:     mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com,
        jolsa@kernel.org, namhyung@kernel.org, irogers@google.com,
        adrian.hunter@intel.com, linux-perf-users@vger.kernel.org,
        linux-kernel@vger.kernel.org, bpf@vger.kernel.org
References: <20230612052452.53425-1-xueshuai@linux.alibaba.com>
 <20230612052452.53425-3-xueshuai@linux.alibaba.com>
From:   James Clark <james.clark@arm.com>
In-Reply-To: <20230612052452.53425-3-xueshuai@linux.alibaba.com>
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Precedence: bulk


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@linux.alibaba.com>
> ---
>  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