Messages in this thread | | | Date | Thu, 7 May 2020 18:05:02 +0800 | From | Xiao Yang <> | Subject | Re: [PATCH] tracing: Wait for preempt irq delay thread to finish |
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Hi Steven,
Thanks for your further investigation.
I used the following ways to test your fix patch on my slow vm and didn't see any issue: 1) Insert and remove preemptirq_delay_test in loops. 2) Insert preemptirq_delay_test, write to /sys/kernel/preemptirq_delay_test/trigger and remove preemptirq_delay_test in loops. 3) Ran irqsoff_tracer.tc in loops.
BTW: For irqsoff_tracer.tc, should we extend code to test the burst feature and the sysfs trigger?
Reviewed-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
Thanks, Xiao Yang On 2020/5/6 22:30, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)"<rostedt@goodmis.org> > > Running on a slower machine, it is possible that the preempt delay kernel > thread may still be executing if the module was immediately removed after > added, and this can cause the kernel to crash as the kernel thread might be > executing after its code has been removed. > > There's no reason that the caller of the code shouldn't just wait for the > delay thread to finish, as the thread can also be created by a trigger in > the sysfs code, which also has the same issues. > > Link: http://lore.kernel.org/r/5EA2B0C8.2080706@cn.fujitsu.com > > Cc: stable@vger.kernel.org > Fixes: 793937236d1ee ("lib: Add module for testing preemptoff/irqsoff latency tracers") > Reported-by: Xiao Yang<yangx.jy@cn.fujitsu.com> > Signed-off-by: Steven Rostedt (VMware)<rostedt@goodmis.org> > --- > kernel/trace/preemptirq_delay_test.c | 30 ++++++++++++++++++++++------ > 1 file changed, 24 insertions(+), 6 deletions(-) > > diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c > index 31c0fad4cb9e..c4c86de63cf9 100644 > --- a/kernel/trace/preemptirq_delay_test.c > +++ b/kernel/trace/preemptirq_delay_test.c > @@ -113,22 +113,42 @@ static int preemptirq_delay_run(void *data) > > for (i = 0; i< s; i++) > (testfuncs[i])(i); > + > + set_current_state(TASK_INTERRUPTIBLE); > + while (!kthread_should_stop()) { > + schedule(); > + set_current_state(TASK_INTERRUPTIBLE); > + } > + > + __set_current_state(TASK_RUNNING); > + > return 0; > } > > -static struct task_struct *preemptirq_start_test(void) > +static int preemptirq_run_test(void) > { > + struct task_struct *task; > + > char task_name[50]; > > snprintf(task_name, sizeof(task_name), "%s_test", test_mode); > - return kthread_run(preemptirq_delay_run, NULL, task_name); > + task = kthread_run(preemptirq_delay_run, NULL, task_name); > + if (IS_ERR(task)) > + return PTR_ERR(task); > + if (task) > + kthread_stop(task); > + return 0; > } > > > static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr, > const char *buf, size_t count) > { > - preemptirq_start_test(); > + ssize_t ret; > + > + ret = preemptirq_run_test(); > + if (ret) > + return ret; > return count; > } > > @@ -148,11 +168,9 @@ static struct kobject *preemptirq_delay_kobj; > > static int __init preemptirq_delay_init(void) > { > - struct task_struct *test_task; > int retval; > > - test_task = preemptirq_start_test(); > - retval = PTR_ERR_OR_ZERO(test_task); > + retval = preemptirq_run_test(); > if (retval != 0) > return retval; >
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