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Wed, 09 Mar 2022 13:39:29 -0800 (PST) Received: from [192.168.1.128] ([71.205.29.0]) by smtp.gmail.com with ESMTPSA id c6-20020a056e020bc600b002c6731e7cb8sm1158182ilu.31.2022.03.09.13.39.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Mar 2022 13:39:29 -0800 (PST) Subject: Re: [PATCH 3/3] kfence: test: try to avoid test_gfpzero trigger rcu_stall To: Peng Liu , 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, Shuah Khan References: <20220309014705.1265861-1-liupeng256@huawei.com> <20220309014705.1265861-4-liupeng256@huawei.com> From: Shuah Khan Message-ID: <1dfeea09-cd4a-39fc-18f4-775bec99afa4@linuxfoundation.org> Date: Wed, 9 Mar 2022 14:39:28 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20220309014705.1265861-4-liupeng256@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/8/22 6:47 PM, Peng Liu wrote: > When CONFIG_KFENCE_DYNAMIC_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 > --- > 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(); This sounds like a band-aid - is there a better way to fix this? > } > > for (i = 0; i < size; i++) > thanks, -- Shuah