From: Petr Mladek <pmladek@suse.com>
To: Yannick Cote <ycote@redhat.com>
Cc: live-patching@vger.kernel.org, linux-kselftest@vger.kernel.org,
joe.lawrence@redhat.com
Subject: Re: [PATCH 1/4] selftests/livepatch: rework test-klp-callbacks to use completion variables
Date: Tue, 2 Jun 2020 10:16:55 +0200 [thread overview]
Message-ID: <20200602081654.GI27273@linux-b0ei> (raw)
In-Reply-To: <20200528134849.7890-2-ycote@redhat.com>
On Thu 2020-05-28 09:48:46, Yannick Cote wrote:
> From: Joe Lawrence <joe.lawrence@redhat.com>
>
> 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@redhat.com>
> Signed-off-by: Yannick Cote <ycote@redhat.com>
> ---
> 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
next prev parent reply other threads:[~2020-06-02 8:16 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-28 13:48 [PATCH 0/4] selftests/livepatch: rework of test-klp-{callbacks,shadow_vars} Yannick Cote
2020-05-28 13:48 ` [PATCH 1/4] selftests/livepatch: rework test-klp-callbacks to use completion variables Yannick Cote
2020-06-02 8:16 ` Petr Mladek [this message]
2020-05-28 13:48 ` [PATCH 2/4] selftests/livepatch: rework test-klp-shadow-vars Yannick Cote
2020-06-02 9:25 ` Petr Mladek
2020-05-28 13:48 ` [PATCH 3/4] selftests/livepatch: more verification in test-klp-shadow-vars Yannick Cote
2020-06-01 11:27 ` Miroslav Benes
2020-06-01 11:39 ` Miroslav Benes
2020-06-02 12:35 ` Petr Mladek
2020-05-28 13:48 ` [PATCH 4/4] selftests/livepatch: fix mem leaks " Yannick Cote
2020-06-02 9:57 ` Petr Mladek
2020-05-29 15:12 ` [PATCH 0/4] selftests/livepatch: rework of test-klp-{callbacks,shadow_vars} Joe Lawrence
2020-06-01 11:48 ` Miroslav Benes
2020-06-02 5:01 ` Kamalesh Babulal
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