Hi,
On 8/30/2022 9:13 AM, Martin KaFai Lau wrote:
> On Mon, Aug 29, 2022 at 10:27:52PM +0800, Hou Tao wrote:
>> From: Hou Tao <houtao1@xxxxxxxxxx>
>>
>> When there are concurrent task local storage lookup operations,
>> if updates on per-cpu bpf_task_storage_busy is not preemption-safe,
>> some updates will be lost due to interleave, the final value of
>> bpf_task_storage_busy will not be zero and bpf_task_storage_trylock()
>> on specific cpu will fail forever.
>>
>> So add a test case to ensure the update of per-cpu bpf_task_storage_busy
>> is preemption-safe.
> This test took my setup 1.5 minute to run
> and cannot reproduce after running the test in a loop.
>
> Can it be reproduced in a much shorter time ?
> If not, test_maps is probably a better place to do the test.
I think the answer is No. I have think about adding the test in test_maps, but
the test case needs running a bpf program to check whether the value of
bpf_task_storage_busy is OK, so for simplicity I add it in test_progs.
If the running time is the problem, I can move it into test_maps.
> I assume it can be reproduced in arm with this test? Or it can
> also be reproduced in other platforms with different kconfig.
> Please paste the test failure message and the platform/kconfig
> to reproduce it in the commit message.
On arm64 it can be reproduced probabilistically when CONFIG_PREEMPT is enabled
on 2-cpus VM as show below. You can try to increase the value of nr and loop if
it still can not be reproduced.
test_preemption:PASS:skel_open_and_load 0 nsec
test_preemption:PASS:no mem 0 nsec
test_preemption:PASS:skel_attach 0 nsec
test_preemption:FAIL:bpf_task_storage_get fails unexpected bpf_task_storage_get
fails: actual 0 != expected 1
#174/4 task_local_storage/preemption:FAIL
#174 task_local_storage:FAIL
All error logs:
test_preemption:PASS:skel_open_and_load 0 nsec
test_preemption:PASS:no mem 0 nsec
test_preemption:PASS:skel_attach 0 nsec
test_preemption:FAIL:bpf_task_storage_get fails unexpected bpf_task_storage_get
fails: actual 0 != expected 1
#174/4 task_local_storage/preemption:FAIL
#174 task_local_storage:FAIL
Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED
On x86-64 __this_cpu_{inc|dec} are atomic, so it is not possible to reproduce
the problem.
