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From:   Peng Liu <liupeng256@huawei.com>
To:     <brendanhiggins@google.com>, <glider@google.com>,
        <elver@google.com>, <dvyukov@google.com>,
        <akpm@linux-foundation.org>, <linux-kselftest@vger.kernel.org>,
        <kunit-dev@googlegroups.com>, <linux-kernel@vger.kernel.org>,
        <kasan-dev@googlegroups.com>, <linux-mm@kvack.org>
CC:     <wangkefeng.wang@huawei.com>, <liupeng256@huawei.com>
Subject: [PATCH v2 3/3] kfence: test: try to avoid test_gfpzero trigger rcu_stall
Date:   Wed, 9 Mar 2022 08:37:53 +0000
Message-ID: <20220309083753.1561921-4-liupeng256@huawei.com>
In-Reply-To: <20220309083753.1561921-1-liupeng256@huawei.com>
References: <20220309083753.1561921-1-liupeng256@huawei.com>
MIME-Version: 1.0
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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.

Signed-off-by: Peng Liu <liupeng256@huawei.com>
---
 mm/kfence/kfence_test.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/kfence/kfence_test.c b/mm/kfence/kfence_test.c
index caed6b4eba94..1b50f70a4c0f 100644
--- a/mm/kfence/kfence_test.c
+++ b/mm/kfence/kfence_test.c
@@ -627,6 +627,7 @@ static void test_gfpzero(struct kunit *test)
 			kunit_warn(test, "giving up ... cannot get same object back\n");
 			return;
 		}
+		cond_resched();
 	}
 
 	for (i = 0; i < size; i++)
-- 
2.18.0.huawei.25