Re: exercising current aarch64 kprobe support with systemtap

[William Cohen <wcohen at redhat dot com>]

On 08/04/2016 10:35 AM, Pratyush Anand wrote:
> Hi Will,
> 
> On 04/08/2016:09:56:45 AM, William Cohen wrote:
...
>> Hi,
>>
>> The OOM errors came before the otf_stress_hard_iter_5000 test that previous triggered the infinite unexpected EL1, so can't really say that the proposed patch has fixed the problem.
> 
> Yes, yes, previously also we were getting OOM, and then that OOM was triggering
> infinite unexpected EL1, because OOM message uses WARN_ON() to print, and
> WARN_ON() uses "BRK BUG_BRK_IMM". Now when it is printing though BRK, we were
> hitting kprobe at print_worker_info() which was resulting in unexpected EL1.
> 
> Proposed patch fixes kprobe tracing within none kprobe BRK context such as
> uprobe or WARN_ON() breakpoint handler etc. So, now a kprobe at
> print_worker_info() will work while printing message of WARN_ON().
> 
> 
>>
>> Any thoughts on how to track down the oom issue?  Are you able to replicate it running the systemtap onthefly/kprobes_onthefly.exp tests?
> 
> Sure, will look into. Have reserved a seattle.
> 
> ~Pratyush
> 

Hi Pratyush,

The stack backtrace of http://paste.stg.fedoraproject.org/5375/ is:


[  668.676682] [<fffffc00082386fc>] page_counter_cancel+0x54/0x60
[  668.682508] [<fffffc000823885c>] page_counter_uncharge+0x2c/0x40
[  668.688509] [<fffffc0008239c68>] cancel_charge+0x40/0xe0
[  668.693815] [<fffffc000823fdfc>] mem_cgroup_cancel_charge+0x2c/0x38
[  668.700088] [<fffffc00081c96a8>] uprobe_write_opcode+0x4e8/0x688
[  668.706089] [<fffffc00081c9878>] set_swbp+0x30/0x40
[  668.710962] [<fffffc00081c98e4>] install_breakpoint.isra.10+0x5c/0x2b8
[  668.717484] [<fffffc00081ca6d8>] uprobe_mmap+0x248/0x2a8
[  668.722791] [<fffffc000820fbac>] mmap_region+0x204/0x558
[  668.728097] [<fffffc0008210164>] do_mmap+0x264/0x320
[  668.733057] [<fffffc00081f2238>] vm_mmap_pgoff+0xb0/0xd8
[  668.738363] [<fffffc00081f22d0>] vm_mmap+0x70/0xa0
[  668.743149] [<fffffc00082a62c8>] elf_map+0x80/0xf8
[  668.747934] [<fffffc00082a7a48>] load_elf_binary+0x480/0xb90
[  668.753588] [<fffffc0008252e7c>] search_binary_handler+0xbc/0x210
[  668.759674] [<fffffc0008253810>] do_execveat_common+0x4b0/0x620
[  668.765587] [<fffffc0008253c74>] SyS_execve+0x44/0x58
[  668.770633] [<fffffc0008082c4c>] __sys_trace_return+0x0/0x4

There is some uprobe code running in the traceback.  It looks like things are going wrong when uprobes are being installed on a newly loaded executable.

-Will