From: Peng Liu <liupeng256@xxxxxxxxxx> Subject: kfence: test: try to avoid test_gfpzero trigger rcu_stall When CONFIG_KFENCE_NUM_OBJECTS is set to a big number, kfence kunit-test-case test_gfpzero will eat up nearly all the CPU's resources and rcu_stall is reported as the following log which is cut from a physical server. rcu: INFO: rcu_sched self-detected stall on CPU rcu: 68-....: (14422 ticks this GP) idle=6ce/1/0x4000000000000002 softirq=592/592 fqs=7500 (t=15004 jiffies g=10677 q=20019) Task dump for CPU 68: task:kunit_try_catch state:R running task stack: 0 pid: 9728 ppid: 2 flags:0x0000020a Call trace: dump_backtrace+0x0/0x1e4 show_stack+0x20/0x2c sched_show_task+0x148/0x170 ... rcu_sched_clock_irq+0x70/0x180 update_process_times+0x68/0xb0 tick_sched_handle+0x38/0x74 ... gic_handle_irq+0x78/0x2c0 el1_irq+0xb8/0x140 kfree+0xd8/0x53c test_alloc+0x264/0x310 [kfence_test] test_gfpzero+0xf4/0x840 [kfence_test] kunit_try_run_case+0x48/0x20c kunit_generic_run_threadfn_adapter+0x28/0x34 kthread+0x108/0x13c ret_from_fork+0x10/0x18 To avoid rcu_stall and unacceptable latency, a schedule point is added to test_gfpzero. Link: https://lkml.kernel.org/r/20220309083753.1561921-4-liupeng256@xxxxxxxxxx Signed-off-by: Peng Liu <liupeng256@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Tested-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Wang Kefeng <wangkefeng.wang@xxxxxxxxxx> Cc: Daniel Latypov <dlatypov@xxxxxxxxxx> Cc: David Gow <davidgow@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/kfence/kfence_test.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/kfence/kfence_test.c~kfence-test-try-to-avoid-test_gfpzero-trigger-rcu_stall +++ a/mm/kfence/kfence_test.c @@ -627,6 +627,7 @@ static void test_gfpzero(struct kunit *t kunit_warn(test, "giving up ... cannot get same object back\n"); return; } + cond_resched(); } for (i = 0; i < size; i++) _
