Re: [PATCH v4 1/2] perf/core: Bail out early if the request AUX area is out of bound

[Shuai Xue]

On 2023/8/4 16:59, Leo Yan wrote:
> On Fri, Aug 04, 2023 at 03:29:44PM +0800, Shuai Xue wrote:
>> When perf-record with a large AUX area, e.g 4GB, it fails with:
>>
>>     #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1
>>     failed to mmap with 12 (Cannot allocate memory)
>>
>> and it reveals a WARNING with __alloc_pages():
>>
>> [   66.595604] ------------[ cut here ]------------
>> [   66.600206] WARNING: CPU: 44 PID: 17573 at mm/page_alloc.c:5568 __alloc_pages+0x1ec/0x248
>> [   66.608375] Modules linked in: ip6table_filter(E) ip6_tables(E) iptable_filter(E) ebtable_nat(E) ebtables(E) aes_ce_blk(E) vfat(E) fat(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)
>> [   66.657719] CPU: 44 PID: 17573 Comm: perf Kdump: loaded Tainted: G            E      6.3.0-rc4+ #58
>> [   66.666749] Hardware name: Default Default/Default, BIOS 1.2.M1.AL.P.139.00 03/22/2023
>> [   66.674650] pstate: 23400009 (nzCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
>> [   66.681597] pc : __alloc_pages+0x1ec/0x248
>> [   66.685680] lr : __kmalloc_large_node+0xc0/0x1f8
>> [   66.690285] sp : ffff800020523980
>> [   66.693585] pmr_save: 000000e0
>> [   66.696624] x29: ffff800020523980 x28: ffff000832975800 x27: 0000000000000000
>> [   66.703746] x26: 0000000000100000 x25: 0000000000100000 x24: ffff8000083615d0
>> [   66.710866] x23: 0000000000040dc0 x22: ffff000823d6d140 x21: 000000000000000b
>> [   66.717987] x20: 000000000000000b x19: 0000000000000000 x18: 0000000000000030
>> [   66.725108] x17: 0000000000000000 x16: ffff800008f05be8 x15: ffff000823d6d6d0
>> [   66.732229] x14: 0000000000000000 x13: 343373656761705f x12: 726e202c30206574
>> [   66.739350] x11: 00000000ffff7fff x10: 00000000ffff7fff x9 : ffff8000083af570
>> [   66.746471] x8 : 00000000000bffe8 x7 : c0000000ffff7fff x6 : 000000000005fff4
>> [   66.753592] x5 : 0000000000000000 x4 : ffff000823d6d8d8 x3 : 0000000000000000
>> [   66.760713] x2 : 0000000000000000 x1 : 0000000000000001 x0 : 0000000000040dc0
>> [   66.767834] Call trace:
>> [   66.770267]  __alloc_pages+0x1ec/0x248
>> [   66.774003]  __kmalloc_large_node+0xc0/0x1f8
>> [   66.778259]  __kmalloc_node+0x134/0x1e8
>> [   66.782081]  rb_alloc_aux+0xe0/0x298
>> [   66.785643]  perf_mmap+0x440/0x660
>> [   66.789031]  mmap_region+0x308/0x8a8
>> [   66.792593]  do_mmap+0x3c0/0x528
>> [   66.795807]  vm_mmap_pgoff+0xf4/0x1b8
>> [   66.799456]  ksys_mmap_pgoff+0x18c/0x218
>> [   66.803365]  __arm64_sys_mmap+0x38/0x58
>> [   66.807187]  invoke_syscall+0x50/0x128
>> [   66.810922]  el0_svc_common.constprop.0+0x58/0x188
>> [   66.815698]  do_el0_svc+0x34/0x50
>> [   66.818999]  el0_svc+0x34/0x108
>> [   66.822127]  el0t_64_sync_handler+0xb8/0xc0
>> [   66.826296]  el0t_64_sync+0x1a4/0x1a8
>> [   66.829946] ---[ end trace 0000000000000000 ]---
>>
>> 'rb->aux_pages' allocated by kcalloc() is a pointer array which is used to
>> maintains AUX trace pages. The allocated page for this array is physically
>> contiguous (and virtually contiguous) with an order of 0..MAX_ORDER. If the
>> size of pointer array crosses the limitation set by MAX_ORDER, it reveals a
>> WARNING.
>>
>> So bail out early with -ENOMEM if the request AUX area is out of bound,
>> e.g.:
>>
>>     #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1
>>     failed to mmap with 12 (Cannot allocate memory)
>>
>> Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
>> ---
>>  kernel/events/ring_buffer.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
>> index a0433f37b024..c445e927368d 100644
>> --- a/kernel/events/ring_buffer.c
>> +++ b/kernel/events/ring_buffer.c
>> @@ -699,6 +699,9 @@ int rb_alloc_aux(struct perf_buffer *rb, struct perf_event *event,
>>  		watermark = 0;
>>  	}
>>  
>> +	/* Can't allocate more than MAX_ORDER */
> 
> The comment is confused.  I'd like to refine it as:
> 
>   /*
>    * kcalloc_node() is unable to allocate buffer if the size is larger
>    * than: PAGE_SIZE << MAX_ORDER; directly bail out in this case.
>    */

Hi, Leo,

Thank you for your quick feedback. The comment is simplified from Peter's reply in v2
version. Your refined comment is more detailed and it makes sense to me, I would like
to adopt it if @Peter has no other opinions.

> To be honest, I am not sure if perf core maintainers like this kind
> thing or not.  Please seek their opinion before you move forward.
> 

and hi, all perf core maintainers,

I have not received explicit objection from perf core maintainers @Peter or @James so
I moved forward to address their comments. It's fine to me to wait for more opinions from
perf core maintainers.

Best Regards,
Shuai