On Sun, May 10, 2020 at 11:42:10AM -0400, Steven Rostedt wrote: > \From: "Steven Rostedt (VMware)" <[email protected]> > > A bug report was posted that running the preempt irq delay module on a slow > machine, and removing it quickly could lead to the thread created by the > modlue to execute after the module is removed, and this could cause the > kernel to crash. The fix for this was to call kthread_stop() after creating > the thread to make sure it finishes before allowing the module to be > removed. > > Now this caused the opposite problem on fast machines. What now happens is > the kthread_stop() can cause the kthread never to execute and the test never > to run. To fix this, add a completion and wait for the kthread to execute, > then wait for it to end. > > This issue caused the ftracetest selftests to fail on the preemptirq tests. > > Cc: [email protected] > Fixes: d16a8c31077e ("tracing: Wait for preempt irq delay thread to finish")
Reviewed-by: Joel Fernandes (Google) <[email protected]> thanks, - Joel > Signed-off-by: Steven Rostedt (VMware) <[email protected]> > --- > kernel/trace/preemptirq_delay_test.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/preemptirq_delay_test.c > b/kernel/trace/preemptirq_delay_test.c > index c4c86de63cf9..312d1a0ca3b6 100644 > --- a/kernel/trace/preemptirq_delay_test.c > +++ b/kernel/trace/preemptirq_delay_test.c > @@ -16,6 +16,7 @@ > #include <linux/printk.h> > #include <linux/string.h> > #include <linux/sysfs.h> > +#include <linux/completion.h> > > static ulong delay = 100; > static char test_mode[12] = "irq"; > @@ -28,6 +29,8 @@ MODULE_PARM_DESC(delay, "Period in microseconds (100 us > default)"); > MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt, irq, or > alternate (default irq)"); > MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)"); > > +static struct completion done; > + > #define MIN(x, y) ((x) < (y) ? (x) : (y)) > > static void busy_wait(ulong time) > @@ -114,6 +117,8 @@ static int preemptirq_delay_run(void *data) > for (i = 0; i < s; i++) > (testfuncs[i])(i); > > + complete(&done); > + > set_current_state(TASK_INTERRUPTIBLE); > while (!kthread_should_stop()) { > schedule(); > @@ -128,15 +133,18 @@ static int preemptirq_delay_run(void *data) > static int preemptirq_run_test(void) > { > struct task_struct *task; > - > char task_name[50]; > > + init_completion(&done); > + > snprintf(task_name, sizeof(task_name), "%s_test", test_mode); > task = kthread_run(preemptirq_delay_run, NULL, task_name); > if (IS_ERR(task)) > return PTR_ERR(task); > - if (task) > + if (task) { > + wait_for_completion(&done); > kthread_stop(task); > + } > return 0; > } > > -- > 2.20.1 >
