The following two patches solve an issue reported by Steffen Trumtrar
and Tim Sander to the linux-rt-users mailing list. Namely, the wakeup
of the watchdogd thread being starved by an RT task due to the hrtimer
deferral through ktimersoftd (on PREEMPT_RT_FULL).
The first patch adjusts the kthread_worker locking to make use of a raw
spinlock, making it suitable for work item queueing from hardirq context
on PREEMPT_RT. This patch can be applied directly to mainline without
any functional change.
The second patch adjusts the hrtimer used by the watchdog core to be a
_HARD timer (and thus not deferred through ktimersoftd w/ PREEMPT_RT).
This patch depends on hrtimer patches carried in the RT patch, and so
should therefore land there.
Cc: Guenter Roeck <[email protected]>
Cc: Steffen Trumtrar <[email protected]>
Cc: Tim Sander <[email protected]>
Julia Cartwright (2):
kthread: convert worker lock to raw spinlock
watchdog, rt: prevent deferral of watchdogd wakeup
drivers/watchdog/watchdog_dev.c | 2 +-
include/linux/kthread.h | 2 +-
kernel/kthread.c | 42 ++++++++++++++++-----------------
3 files changed, 23 insertions(+), 23 deletions(-)
--
2.18.0
When PREEMPT_RT_FULL is enabled, all hrtimer expiry functions are
deferred for execution into the context of ktimersoftd unless otherwise
annotated.
Deferring the expiry of the hrtimer used by the watchdog core, however,
is a waste, as the callback does nothing but queue a kthread work item
and wakeup watchdogd.
It's worst then that, too: the deferral through ktimersoftd also means
that for correct behavior a user must adjust the scheduling parameters
of both watchdogd _and_ ktimersoftd, which is unnecessary and has other
side effects (like causing unrelated expiry functions to execute at
potentially elevated priority).
Instead, mark the hrtimer used by the watchdog core as being _HARD to
allow it's execution directly from hardirq context. The work done in
this expiry function is well-bounded and minimal.
A user still must adjust the scheduling parameters of the watchdogd
to be correct w.r.t. their application needs.
Cc: Guenter Roeck <[email protected]>
Reported-and-tested-by: Steffen Trumtrar <[email protected]>
Reported-by: Tim Sander <[email protected]>
Signed-off-by: Julia Cartwright <[email protected]>
---
drivers/watchdog/watchdog_dev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index ffbdc4642ea5..9c2b3e5cebdc 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -945,7 +945,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
return -ENODEV;
kthread_init_work(&wd_data->work, watchdog_ping_work);
- hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
wd_data->timer.function = watchdog_timer_expired;
if (wdd->id == 0) {
--
2.18.0
In order to enable the queuing of kthread work items from hardirq
context even when PREEMPT_RT_FULL is enabled, convert the worker
spin_lock to a raw_spin_lock.
This is only acceptable to do because the work performed under the lock
is well-bounded and minimal.
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Guenter Roeck <[email protected]>
Reported-and-tested-by: Steffen Trumtrar <[email protected]>
Reported-by: Tim Sander <[email protected]>
Signed-off-by: Julia Cartwright <[email protected]>
---
include/linux/kthread.h | 2 +-
kernel/kthread.c | 42 ++++++++++++++++++++---------------------
2 files changed, 22 insertions(+), 22 deletions(-)
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index c1961761311d..ad292898f7f2 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -85,7 +85,7 @@ enum {
struct kthread_worker {
unsigned int flags;
- spinlock_t lock;
+ raw_spinlock_t lock;
struct list_head work_list;
struct list_head delayed_work_list;
struct task_struct *task;
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 486dedbd9af5..c1d9ee6671c6 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -597,7 +597,7 @@ void __kthread_init_worker(struct kthread_worker *worker,
struct lock_class_key *key)
{
memset(worker, 0, sizeof(struct kthread_worker));
- spin_lock_init(&worker->lock);
+ raw_spin_lock_init(&worker->lock);
lockdep_set_class_and_name(&worker->lock, key, name);
INIT_LIST_HEAD(&worker->work_list);
INIT_LIST_HEAD(&worker->delayed_work_list);
@@ -639,21 +639,21 @@ int kthread_worker_fn(void *worker_ptr)
if (kthread_should_stop()) {
__set_current_state(TASK_RUNNING);
- spin_lock_irq(&worker->lock);
+ raw_spin_lock_irq(&worker->lock);
worker->task = NULL;
- spin_unlock_irq(&worker->lock);
+ raw_spin_unlock_irq(&worker->lock);
return 0;
}
work = NULL;
- spin_lock_irq(&worker->lock);
+ raw_spin_lock_irq(&worker->lock);
if (!list_empty(&worker->work_list)) {
work = list_first_entry(&worker->work_list,
struct kthread_work, node);
list_del_init(&work->node);
}
worker->current_work = work;
- spin_unlock_irq(&worker->lock);
+ raw_spin_unlock_irq(&worker->lock);
if (work) {
__set_current_state(TASK_RUNNING);
@@ -810,12 +810,12 @@ bool kthread_queue_work(struct kthread_worker *worker,
bool ret = false;
unsigned long flags;
- spin_lock_irqsave(&worker->lock, flags);
+ raw_spin_lock_irqsave(&worker->lock, flags);
if (!queuing_blocked(worker, work)) {
kthread_insert_work(worker, work, &worker->work_list);
ret = true;
}
- spin_unlock_irqrestore(&worker->lock, flags);
+ raw_spin_unlock_irqrestore(&worker->lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(kthread_queue_work);
@@ -841,7 +841,7 @@ void kthread_delayed_work_timer_fn(struct timer_list *t)
if (WARN_ON_ONCE(!worker))
return;
- spin_lock(&worker->lock);
+ raw_spin_lock(&worker->lock);
/* Work must not be used with >1 worker, see kthread_queue_work(). */
WARN_ON_ONCE(work->worker != worker);
@@ -850,7 +850,7 @@ void kthread_delayed_work_timer_fn(struct timer_list *t)
list_del_init(&work->node);
kthread_insert_work(worker, work, &worker->work_list);
- spin_unlock(&worker->lock);
+ raw_spin_unlock(&worker->lock);
}
EXPORT_SYMBOL(kthread_delayed_work_timer_fn);
@@ -906,14 +906,14 @@ bool kthread_queue_delayed_work(struct kthread_worker *worker,
unsigned long flags;
bool ret = false;
- spin_lock_irqsave(&worker->lock, flags);
+ raw_spin_lock_irqsave(&worker->lock, flags);
if (!queuing_blocked(worker, work)) {
__kthread_queue_delayed_work(worker, dwork, delay);
ret = true;
}
- spin_unlock_irqrestore(&worker->lock, flags);
+ raw_spin_unlock_irqrestore(&worker->lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);
@@ -949,7 +949,7 @@ void kthread_flush_work(struct kthread_work *work)
if (!worker)
return;
- spin_lock_irq(&worker->lock);
+ raw_spin_lock_irq(&worker->lock);
/* Work must not be used with >1 worker, see kthread_queue_work(). */
WARN_ON_ONCE(work->worker != worker);
@@ -961,7 +961,7 @@ void kthread_flush_work(struct kthread_work *work)
else
noop = true;
- spin_unlock_irq(&worker->lock);
+ raw_spin_unlock_irq(&worker->lock);
if (!noop)
wait_for_completion(&fwork.done);
@@ -994,9 +994,9 @@ static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork,
* any queuing is blocked by setting the canceling counter.
*/
work->canceling++;
- spin_unlock_irqrestore(&worker->lock, *flags);
+ raw_spin_unlock_irqrestore(&worker->lock, *flags);
del_timer_sync(&dwork->timer);
- spin_lock_irqsave(&worker->lock, *flags);
+ raw_spin_lock_irqsave(&worker->lock, *flags);
work->canceling--;
}
@@ -1043,7 +1043,7 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker,
unsigned long flags;
int ret = false;
- spin_lock_irqsave(&worker->lock, flags);
+ raw_spin_lock_irqsave(&worker->lock, flags);
/* Do not bother with canceling when never queued. */
if (!work->worker)
@@ -1060,7 +1060,7 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker,
fast_queue:
__kthread_queue_delayed_work(worker, dwork, delay);
out:
- spin_unlock_irqrestore(&worker->lock, flags);
+ raw_spin_unlock_irqrestore(&worker->lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);
@@ -1074,7 +1074,7 @@ static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
if (!worker)
goto out;
- spin_lock_irqsave(&worker->lock, flags);
+ raw_spin_lock_irqsave(&worker->lock, flags);
/* Work must not be used with >1 worker, see kthread_queue_work(). */
WARN_ON_ONCE(work->worker != worker);
@@ -1088,13 +1088,13 @@ static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
* In the meantime, block any queuing by setting the canceling counter.
*/
work->canceling++;
- spin_unlock_irqrestore(&worker->lock, flags);
+ raw_spin_unlock_irqrestore(&worker->lock, flags);
kthread_flush_work(work);
- spin_lock_irqsave(&worker->lock, flags);
+ raw_spin_lock_irqsave(&worker->lock, flags);
work->canceling--;
out_fast:
- spin_unlock_irqrestore(&worker->lock, flags);
+ raw_spin_unlock_irqrestore(&worker->lock, flags);
out:
return ret;
}
--
2.18.0
Hi Julia,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on linus/master]
[also build test ERROR on v4.19-rc5 next-20180928]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Julia-Cartwright/kthread-convert-worker-lock-to-raw-spinlock/20180929-052522
config: i386-randconfig-x008-201838 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All errors (new ones prefixed by >>):
drivers//watchdog/watchdog_dev.c: In function 'watchdog_cdev_register':
>> drivers//watchdog/watchdog_dev.c:948:49: error: 'HRTIMER_MODE_REL_HARD' undeclared (first use in this function); did you mean 'HRTIMER_MODE_REL_SOFT'?
hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
^~~~~~~~~~~~~~~~~~~~~
HRTIMER_MODE_REL_SOFT
drivers//watchdog/watchdog_dev.c:948:49: note: each undeclared identifier is reported only once for each function it appears in
vim +948 drivers//watchdog/watchdog_dev.c
919
920 /*
921 * watchdog_cdev_register: register watchdog character device
922 * @wdd: watchdog device
923 * @devno: character device number
924 *
925 * Register a watchdog character device including handling the legacy
926 * /dev/watchdog node. /dev/watchdog is actually a miscdevice and
927 * thus we set it up like that.
928 */
929
930 static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
931 {
932 struct watchdog_core_data *wd_data;
933 int err;
934
935 wd_data = kzalloc(sizeof(struct watchdog_core_data), GFP_KERNEL);
936 if (!wd_data)
937 return -ENOMEM;
938 kref_init(&wd_data->kref);
939 mutex_init(&wd_data->lock);
940
941 wd_data->wdd = wdd;
942 wdd->wd_data = wd_data;
943
944 if (IS_ERR_OR_NULL(watchdog_kworker))
945 return -ENODEV;
946
947 kthread_init_work(&wd_data->work, watchdog_ping_work);
> 948 hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
949 wd_data->timer.function = watchdog_timer_expired;
950
951 if (wdd->id == 0) {
952 old_wd_data = wd_data;
953 watchdog_miscdev.parent = wdd->parent;
954 err = misc_register(&watchdog_miscdev);
955 if (err != 0) {
956 pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
957 wdd->info->identity, WATCHDOG_MINOR, err);
958 if (err == -EBUSY)
959 pr_err("%s: a legacy watchdog module is probably present.\n",
960 wdd->info->identity);
961 old_wd_data = NULL;
962 kfree(wd_data);
963 return err;
964 }
965 }
966
967 /* Fill in the data structures */
968 cdev_init(&wd_data->cdev, &watchdog_fops);
969 wd_data->cdev.owner = wdd->ops->owner;
970
971 /* Add the device */
972 err = cdev_add(&wd_data->cdev, devno, 1);
973 if (err) {
974 pr_err("watchdog%d unable to add device %d:%d\n",
975 wdd->id, MAJOR(watchdog_devt), wdd->id);
976 if (wdd->id == 0) {
977 misc_deregister(&watchdog_miscdev);
978 old_wd_data = NULL;
979 kref_put(&wd_data->kref, watchdog_core_data_release);
980 }
981 return err;
982 }
983
984 /* Record time of most recent heartbeat as 'just before now'. */
985 wd_data->last_hw_keepalive = ktime_sub(ktime_get(), 1);
986
987 /*
988 * If the watchdog is running, prevent its driver from being unloaded,
989 * and schedule an immediate ping.
990 */
991 if (watchdog_hw_running(wdd)) {
992 __module_get(wdd->ops->owner);
993 kref_get(&wd_data->kref);
994 if (handle_boot_enabled)
995 hrtimer_start(&wd_data->timer, 0, HRTIMER_MODE_REL);
996 else
997 pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n",
998 wdd->id);
999 }
1000
1001 return 0;
1002 }
1003
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
Hi Julia,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on linus/master]
[also build test ERROR on v4.19-rc5 next-20180928]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Julia-Cartwright/kthread-convert-worker-lock-to-raw-spinlock/20180929-052522
config: i386-randconfig-s0-201838 (attached as .config)
compiler: gcc-6 (Debian 6.4.0-9) 6.4.0 20171026
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All errors (new ones prefixed by >>):
drivers//watchdog/watchdog_dev.c: In function 'watchdog_cdev_register':
>> drivers//watchdog/watchdog_dev.c:948:49: error: 'HRTIMER_MODE_REL_HARD' undeclared (first use in this function)
hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
^~~~~~~~~~~~~~~~~~~~~
drivers//watchdog/watchdog_dev.c:948:49: note: each undeclared identifier is reported only once for each function it appears in
vim +/HRTIMER_MODE_REL_HARD +948 drivers//watchdog/watchdog_dev.c
919
920 /*
921 * watchdog_cdev_register: register watchdog character device
922 * @wdd: watchdog device
923 * @devno: character device number
924 *
925 * Register a watchdog character device including handling the legacy
926 * /dev/watchdog node. /dev/watchdog is actually a miscdevice and
927 * thus we set it up like that.
928 */
929
930 static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
931 {
932 struct watchdog_core_data *wd_data;
933 int err;
934
935 wd_data = kzalloc(sizeof(struct watchdog_core_data), GFP_KERNEL);
936 if (!wd_data)
937 return -ENOMEM;
938 kref_init(&wd_data->kref);
939 mutex_init(&wd_data->lock);
940
941 wd_data->wdd = wdd;
942 wdd->wd_data = wd_data;
943
944 if (IS_ERR_OR_NULL(watchdog_kworker))
945 return -ENODEV;
946
947 kthread_init_work(&wd_data->work, watchdog_ping_work);
> 948 hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
949 wd_data->timer.function = watchdog_timer_expired;
950
951 if (wdd->id == 0) {
952 old_wd_data = wd_data;
953 watchdog_miscdev.parent = wdd->parent;
954 err = misc_register(&watchdog_miscdev);
955 if (err != 0) {
956 pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
957 wdd->info->identity, WATCHDOG_MINOR, err);
958 if (err == -EBUSY)
959 pr_err("%s: a legacy watchdog module is probably present.\n",
960 wdd->info->identity);
961 old_wd_data = NULL;
962 kfree(wd_data);
963 return err;
964 }
965 }
966
967 /* Fill in the data structures */
968 cdev_init(&wd_data->cdev, &watchdog_fops);
969 wd_data->cdev.owner = wdd->ops->owner;
970
971 /* Add the device */
972 err = cdev_add(&wd_data->cdev, devno, 1);
973 if (err) {
974 pr_err("watchdog%d unable to add device %d:%d\n",
975 wdd->id, MAJOR(watchdog_devt), wdd->id);
976 if (wdd->id == 0) {
977 misc_deregister(&watchdog_miscdev);
978 old_wd_data = NULL;
979 kref_put(&wd_data->kref, watchdog_core_data_release);
980 }
981 return err;
982 }
983
984 /* Record time of most recent heartbeat as 'just before now'. */
985 wd_data->last_hw_keepalive = ktime_sub(ktime_get(), 1);
986
987 /*
988 * If the watchdog is running, prevent its driver from being unloaded,
989 * and schedule an immediate ping.
990 */
991 if (watchdog_hw_running(wdd)) {
992 __module_get(wdd->ops->owner);
993 kref_get(&wd_data->kref);
994 if (handle_boot_enabled)
995 hrtimer_start(&wd_data->timer, 0, HRTIMER_MODE_REL);
996 else
997 pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n",
998 wdd->id);
999 }
1000
1001 return 0;
1002 }
1003
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
On Sat, 29 Sep 2018, kbuild test robot wrote:
> [also build test ERROR on v4.19-rc5 next-20180928]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>
It's against the RT tree, so it won't work against next or upstream. I
think it would be good to have a machine parseable tag to describe which
tree/branch/commit patches are applicable to. If that tag is missing, the
bot can assume it's against upstream/next.
Thanks,
tglx
On 2018-09-29 08:38:55 [+0200], Thomas Gleixner wrote:
> On Sat, 29 Sep 2018, kbuild test robot wrote:
> > [also build test ERROR on v4.19-rc5 next-20180928]
> > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> >
>
> It's against the RT tree, so it won't work against next or upstream. I
> think it would be good to have a machine parseable tag to describe which
> tree/branch/commit patches are applicable to. If that tag is missing, the
> bot can assume it's against upstream/next.
I asked the testing team to ignore patches or test against the RT tree
if the patch is tagged [PATCH RT]. I think it worked since I haven't
seen those mails.
> Thanks,
>
> tglx
Sebastian
> Subject: Re: [kbuild-all] [PATCH RT 2/2] watchdog, rt: prevent deferral of
> watchdogd wakeup
>
> On 2018-09-29 08:38:55 [+0200], Thomas Gleixner wrote:
> > On Sat, 29 Sep 2018, kbuild test robot wrote:
> > > [also build test ERROR on v4.19-rc5 next-20180928]
> > > [if your patch is applied to the wrong git tree, please drop us a note to help
> improve the system]
> > >
> >
> > It's against the RT tree, so it won't work against next or upstream. I
> > think it would be good to have a machine parseable tag to describe which
> > tree/branch/commit patches are applicable to. If that tag is missing, the
> > bot can assume it's against upstream/next.
>
> I asked the testing team to ignore patches or test against the RT tree
> if the patch is tagged [PATCH RT]. I think it worked since I haven't
> seen those mails.
thanks Sebastian for the input, we will consider this to add to our TODO.
>
> > Thanks,
> >
> > tglx
>
> Sebastian
> _______________________________________________
> kbuild-all mailing list
> [email protected]
> https://lists.01.org/mailman/listinfo/kbuild-all
On 09/28/2018 02:03 PM, Julia Cartwright wrote:
> When PREEMPT_RT_FULL is enabled, all hrtimer expiry functions are
> deferred for execution into the context of ktimersoftd unless otherwise
> annotated.
>
> Deferring the expiry of the hrtimer used by the watchdog core, however,
> is a waste, as the callback does nothing but queue a kthread work item
> and wakeup watchdogd.
>
> It's worst then that, too: the deferral through ktimersoftd also means
> that for correct behavior a user must adjust the scheduling parameters
> of both watchdogd _and_ ktimersoftd, which is unnecessary and has other
> side effects (like causing unrelated expiry functions to execute at
> potentially elevated priority).
>
> Instead, mark the hrtimer used by the watchdog core as being _HARD to
> allow it's execution directly from hardirq context. The work done in
> this expiry function is well-bounded and minimal.
>
> A user still must adjust the scheduling parameters of the watchdogd
> to be correct w.r.t. their application needs.
>
> Cc: Guenter Roeck <[email protected]>
> Reported-and-tested-by: Steffen Trumtrar <[email protected]>
> Reported-by: Tim Sander <[email protected]>
> Signed-off-by: Julia Cartwright <[email protected]>
Acked-by: Guenter Roeck <[email protected]>
> ---
> drivers/watchdog/watchdog_dev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index ffbdc4642ea5..9c2b3e5cebdc 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -945,7 +945,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
> return -ENODEV;
>
> kthread_init_work(&wd_data->work, watchdog_ping_work);
> - hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
> wd_data->timer.function = watchdog_timer_expired;
>
> if (wdd->id == 0) {
>
On 2018-09-28 21:03:51 [+0000], Julia Cartwright wrote:
> In order to enable the queuing of kthread work items from hardirq
> context even when PREEMPT_RT_FULL is enabled, convert the worker
> spin_lock to a raw_spin_lock.
>
> This is only acceptable to do because the work performed under the lock
> is well-bounded and minimal.
>
> Cc: Sebastian Andrzej Siewior <[email protected]>
> Cc: Guenter Roeck <[email protected]>
> Reported-and-tested-by: Steffen Trumtrar <[email protected]>
> Reported-by: Tim Sander <[email protected]>
> Signed-off-by: Julia Cartwright <[email protected]>
Acked-by: Sebastian Andrzej Siewior <[email protected]>
Sebastian
On 2018-09-28 21:03:51 [+0000], Julia Cartwright wrote:
> When PREEMPT_RT_FULL is enabled, all hrtimer expiry functions are
> deferred for execution into the context of ktimersoftd unless otherwise
> annotated.
…
> Signed-off-by: Julia Cartwright <[email protected]>
did s@HRTIMER_MODE_REL@HRTIMER_MODE_REL_HARD@ and then applied.
Thank you Julia.
Sebastian
Hi Julia,
On Fri, Sep 28, 2018 at 09:03:51PM +0000, Julia Cartwright wrote:
> In order to enable the queuing of kthread work items from hardirq
> context even when PREEMPT_RT_FULL is enabled, convert the worker
> spin_lock to a raw_spin_lock.
>
> This is only acceptable to do because the work performed under the lock
> is well-bounded and minimal.
Clearly not my topic..., but out of curiosity: What do you mean by
"well-bounded" and "minimal"? Can you maybe point me to some doc.?
Andrea
>
> Cc: Sebastian Andrzej Siewior <[email protected]>
> Cc: Guenter Roeck <[email protected]>
> Reported-and-tested-by: Steffen Trumtrar <[email protected]>
> Reported-by: Tim Sander <[email protected]>
> Signed-off-by: Julia Cartwright <[email protected]>
> ---
> include/linux/kthread.h | 2 +-
> kernel/kthread.c | 42 ++++++++++++++++++++---------------------
> 2 files changed, 22 insertions(+), 22 deletions(-)
>
> diff --git a/include/linux/kthread.h b/include/linux/kthread.h
> index c1961761311d..ad292898f7f2 100644
> --- a/include/linux/kthread.h
> +++ b/include/linux/kthread.h
> @@ -85,7 +85,7 @@ enum {
>
> struct kthread_worker {
> unsigned int flags;
> - spinlock_t lock;
> + raw_spinlock_t lock;
> struct list_head work_list;
> struct list_head delayed_work_list;
> struct task_struct *task;
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 486dedbd9af5..c1d9ee6671c6 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -597,7 +597,7 @@ void __kthread_init_worker(struct kthread_worker *worker,
> struct lock_class_key *key)
> {
> memset(worker, 0, sizeof(struct kthread_worker));
> - spin_lock_init(&worker->lock);
> + raw_spin_lock_init(&worker->lock);
> lockdep_set_class_and_name(&worker->lock, key, name);
> INIT_LIST_HEAD(&worker->work_list);
> INIT_LIST_HEAD(&worker->delayed_work_list);
> @@ -639,21 +639,21 @@ int kthread_worker_fn(void *worker_ptr)
>
> if (kthread_should_stop()) {
> __set_current_state(TASK_RUNNING);
> - spin_lock_irq(&worker->lock);
> + raw_spin_lock_irq(&worker->lock);
> worker->task = NULL;
> - spin_unlock_irq(&worker->lock);
> + raw_spin_unlock_irq(&worker->lock);
> return 0;
> }
>
> work = NULL;
> - spin_lock_irq(&worker->lock);
> + raw_spin_lock_irq(&worker->lock);
> if (!list_empty(&worker->work_list)) {
> work = list_first_entry(&worker->work_list,
> struct kthread_work, node);
> list_del_init(&work->node);
> }
> worker->current_work = work;
> - spin_unlock_irq(&worker->lock);
> + raw_spin_unlock_irq(&worker->lock);
>
> if (work) {
> __set_current_state(TASK_RUNNING);
> @@ -810,12 +810,12 @@ bool kthread_queue_work(struct kthread_worker *worker,
> bool ret = false;
> unsigned long flags;
>
> - spin_lock_irqsave(&worker->lock, flags);
> + raw_spin_lock_irqsave(&worker->lock, flags);
> if (!queuing_blocked(worker, work)) {
> kthread_insert_work(worker, work, &worker->work_list);
> ret = true;
> }
> - spin_unlock_irqrestore(&worker->lock, flags);
> + raw_spin_unlock_irqrestore(&worker->lock, flags);
> return ret;
> }
> EXPORT_SYMBOL_GPL(kthread_queue_work);
> @@ -841,7 +841,7 @@ void kthread_delayed_work_timer_fn(struct timer_list *t)
> if (WARN_ON_ONCE(!worker))
> return;
>
> - spin_lock(&worker->lock);
> + raw_spin_lock(&worker->lock);
> /* Work must not be used with >1 worker, see kthread_queue_work(). */
> WARN_ON_ONCE(work->worker != worker);
>
> @@ -850,7 +850,7 @@ void kthread_delayed_work_timer_fn(struct timer_list *t)
> list_del_init(&work->node);
> kthread_insert_work(worker, work, &worker->work_list);
>
> - spin_unlock(&worker->lock);
> + raw_spin_unlock(&worker->lock);
> }
> EXPORT_SYMBOL(kthread_delayed_work_timer_fn);
>
> @@ -906,14 +906,14 @@ bool kthread_queue_delayed_work(struct kthread_worker *worker,
> unsigned long flags;
> bool ret = false;
>
> - spin_lock_irqsave(&worker->lock, flags);
> + raw_spin_lock_irqsave(&worker->lock, flags);
>
> if (!queuing_blocked(worker, work)) {
> __kthread_queue_delayed_work(worker, dwork, delay);
> ret = true;
> }
>
> - spin_unlock_irqrestore(&worker->lock, flags);
> + raw_spin_unlock_irqrestore(&worker->lock, flags);
> return ret;
> }
> EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);
> @@ -949,7 +949,7 @@ void kthread_flush_work(struct kthread_work *work)
> if (!worker)
> return;
>
> - spin_lock_irq(&worker->lock);
> + raw_spin_lock_irq(&worker->lock);
> /* Work must not be used with >1 worker, see kthread_queue_work(). */
> WARN_ON_ONCE(work->worker != worker);
>
> @@ -961,7 +961,7 @@ void kthread_flush_work(struct kthread_work *work)
> else
> noop = true;
>
> - spin_unlock_irq(&worker->lock);
> + raw_spin_unlock_irq(&worker->lock);
>
> if (!noop)
> wait_for_completion(&fwork.done);
> @@ -994,9 +994,9 @@ static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork,
> * any queuing is blocked by setting the canceling counter.
> */
> work->canceling++;
> - spin_unlock_irqrestore(&worker->lock, *flags);
> + raw_spin_unlock_irqrestore(&worker->lock, *flags);
> del_timer_sync(&dwork->timer);
> - spin_lock_irqsave(&worker->lock, *flags);
> + raw_spin_lock_irqsave(&worker->lock, *flags);
> work->canceling--;
> }
>
> @@ -1043,7 +1043,7 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker,
> unsigned long flags;
> int ret = false;
>
> - spin_lock_irqsave(&worker->lock, flags);
> + raw_spin_lock_irqsave(&worker->lock, flags);
>
> /* Do not bother with canceling when never queued. */
> if (!work->worker)
> @@ -1060,7 +1060,7 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker,
> fast_queue:
> __kthread_queue_delayed_work(worker, dwork, delay);
> out:
> - spin_unlock_irqrestore(&worker->lock, flags);
> + raw_spin_unlock_irqrestore(&worker->lock, flags);
> return ret;
> }
> EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);
> @@ -1074,7 +1074,7 @@ static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
> if (!worker)
> goto out;
>
> - spin_lock_irqsave(&worker->lock, flags);
> + raw_spin_lock_irqsave(&worker->lock, flags);
> /* Work must not be used with >1 worker, see kthread_queue_work(). */
> WARN_ON_ONCE(work->worker != worker);
>
> @@ -1088,13 +1088,13 @@ static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
> * In the meantime, block any queuing by setting the canceling counter.
> */
> work->canceling++;
> - spin_unlock_irqrestore(&worker->lock, flags);
> + raw_spin_unlock_irqrestore(&worker->lock, flags);
> kthread_flush_work(work);
> - spin_lock_irqsave(&worker->lock, flags);
> + raw_spin_lock_irqsave(&worker->lock, flags);
> work->canceling--;
>
> out_fast:
> - spin_unlock_irqrestore(&worker->lock, flags);
> + raw_spin_unlock_irqrestore(&worker->lock, flags);
> out:
> return ret;
> }
> --
> 2.18.0
>
On 2018-10-05 20:10:35 [+0200], Andrea Parri wrote:
>
> Clearly not my topic..., but out of curiosity: What do you mean by
> "well-bounded" and "minimal"? Can you maybe point me to some doc.?
it means that the lock is not held for an arbitrary amount of time like
by processing a list with thousand items. Well-bounded would mean not
process more than one or five (or so) at a time.
> Andrea
Sebastian