On Thu 2020-05-28 09:48:46, Yannick Cote wrote:
> From: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
>
> The test-klp-callbacks script includes a few tests which rely on kernel
> task timings that may not always execute as expected under system load.
> These will generate out of sequence kernel log messages that result in
> test failure.
>
> Instead of using sleep timing windows to orchestrate the test, rework
> the test_klp_callbacks_busy module to use completion variables.
>
> Signed-off-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
> Signed-off-by: Yannick Cote <ycote@xxxxxxxxxx>
> ---
> lib/livepatch/test_klp_callbacks_busy.c | 42 +++++++++++++++----
> .../selftests/livepatch/test-callbacks.sh | 29 +++++++------
> 2 files changed, 47 insertions(+), 24 deletions(-)
>
> diff --git a/lib/livepatch/test_klp_callbacks_busy.c b/lib/livepatch/test_klp_callbacks_busy.c
> index 40beddf8a0e2..c3df12f47e5e 100644
> --- a/lib/livepatch/test_klp_callbacks_busy.c
> +++ b/lib/livepatch/test_klp_callbacks_busy.c
> @@ -5,34 +5,58 @@
>
> #include <linux/module.h>
> #include <linux/kernel.h>
> +#include <linux/sched.h>
> #include <linux/workqueue.h>
> #include <linux/delay.h>
>
> -static int sleep_secs;
> -module_param(sleep_secs, int, 0644);
> -MODULE_PARM_DESC(sleep_secs, "sleep_secs (default=0)");
> +/* load/run-time control from sysfs writer */
> +static bool block_transition;
> +module_param(block_transition, bool, 0644);
> +MODULE_PARM_DESC(block_transition, "block_transition (default=false)");
>
> static void busymod_work_func(struct work_struct *work);
> -static DECLARE_DELAYED_WORK(work, busymod_work_func);
> +static DECLARE_WORK(work, busymod_work_func);
> +static DECLARE_COMPLETION(busymod_work_complete);
>
> static void busymod_work_func(struct work_struct *work)
> {
> - pr_info("%s, sleeping %d seconds ...\n", __func__, sleep_secs);
> - msleep(sleep_secs * 1000);
> + bool early_complete = block_transition;
> +
> + pr_info("%s enter\n", __func__);
> +
> + /*
> + * When blocking the livepatch transition, set completion flag
> + * early so subsequent test commands see the transition.
> + */
> + if (early_complete)
> + complete(&busymod_work_complete);
I have to say that the code is really confusing. A completion called
"work_complete" is completed when the work gets actually. It is
completed later when the work is done immediately.
Do we need the completion at all? See below.
> +
> + while (block_transition)
The compiler might optimize the code and avoid the re-reads. Please, use:
/* Re-read variable in each cycle */
while (READ_ONCE(block_transition))
> + msleep(1000);
Nit: This is still a busy wait even though there is a big
delay between waits. The right solution would be using wait_event().
But feel free to keep msleep(). It is good enough for selftests.
> +
> pr_info("%s exit\n", __func__);
> +
> + /*
> + * In non-blocking case, wait until we're done to complete to
> + * ensure kernel log ordering
> + */
> + if (!early_complete)
> + complete(&busymod_work_complete);
> }
>
> static int test_klp_callbacks_busy_init(void)
> {
> pr_info("%s\n", __func__);
> - schedule_delayed_work(&work,
> - msecs_to_jiffies(1000 * 0));
> + schedule_work(&work);
> + wait_for_completion(&busymod_work_complete);
IMHO, the completion is not needed when using:
schedule_work(&work);
/*
* Print all messages from the work before returning from init().
* It helps to serialize messages from the loaded modules.
*/
if (!block_transition)
flush_work(&work);
> +
> return 0;
> }
>
> static void test_klp_callbacks_busy_exit(void)
> {
> - cancel_delayed_work_sync(&work);
> + block_transition = false;
The compiler could move this assignment after the following
call. Please, use:
/* Make sure that the variable is set before flushing work. */
WRITE_ONCE(block_transition, false);
> + cancel_work_sync(&work);
The work is not longer canceled. flush_work() better fits here.
Also I would do this only when the transition is blocked:
if (block_transition) {
/* Make sure that the variable is set before flushing work. */
WRITE_ONCE(block_transition, false);
flush_work(&work);
}
Otherwise this is a nice improvement.
Best Regards,
Petr
