[PATCH] softirq: Be more verbose on t->state BUG()

[PATCH] softirq: Be more verbose on t->state BUG()

[Eugeniu Rosca]

From: Dirk Behme <dirk.behme@de.bosch.com>

In case this BUG() is hit, it helps debugging a lot to get an idea
what tasklet is the root cause. So, be slightly more verbose here.

Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
---
 kernel/softirq.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 9908ec4a9bfe..a6b602ad48d6 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -550,9 +550,13 @@ static void tasklet_action_common(struct softirq_action *a,
 
 		if (tasklet_trylock(t)) {
 			if (!atomic_read(&t->count)) {
-				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
-							&t->state))
+				if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
+					if (t->use_callback)
+						pr_emerg("tasklet failed, cb: %pS\n", t->callback);
+					else
+						pr_emerg("tasklet failed, func: %pS\n", t->func);
 					BUG();
+				}
 				if (t->use_callback)
 					t->callback(t);
 				else
-- 
2.29.0

Re: [PATCH] softirq: Be more verbose on t->state BUG()

[Thomas Gleixner]

On Mon, Mar 15 2021 at 16:44, Eugeniu Rosca wrote:
> From: Dirk Behme <dirk.behme@de.bosch.com>
>
> In case this BUG() is hit, it helps debugging a lot to get an idea
> what tasklet is the root cause. So, be slightly more verbose here.
>
> Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
> Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
> ---
>  kernel/softirq.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 9908ec4a9bfe..a6b602ad48d6 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -550,9 +550,13 @@ static void tasklet_action_common(struct softirq_action *a,
>  
>  		if (tasklet_trylock(t)) {
>  			if (!atomic_read(&t->count)) {
> -				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
> -							&t->state))
> +				if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
> +					if (t->use_callback)
> +						pr_emerg("tasklet failed, cb: %pS\n", t->callback);
> +					else
> +						pr_emerg("tasklet failed, func: %pS\n", t->func);
>  					BUG();
> +				}
>  				if (t->use_callback)
>  					t->callback(t);
>  				else

This belongs into unreadable land and actually the BUG() should just be
replaced by a WARN_ONCE(). Something like the below. Hmm?

Thanks,

        tglx
---
 
+static bool tasklet_should_run(struct tasklet_struct *t)
+{
+	if (test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
+		return true;
+
+	WARN_ONCE(1, "tasklet SCHED state not set: %s %pS\n",
+		  t->use_callback ? "callback" : "func",
+		  t->use_callback ? (void*)t->callback : (void*)t->func);
+
+	return false;
+}
+
 static void tasklet_action_common(struct softirq_action *a,
 				  struct tasklet_head *tl_head,
 				  unsigned int softirq_nr)
@@ -550,13 +562,12 @@ static void tasklet_action_common(struct
 
 		if (tasklet_trylock(t)) {
 			if (!atomic_read(&t->count)) {
-				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
-							&t->state))
-					BUG();
-				if (t->use_callback)
-					t->callback(t);
-				else
-					t->func(t->data);
+				if (tasklet_should_run(t)) {
+					if (t->use_callback)
+						t->callback(t);
+					else
+						t->func(t->data);
+				}
 				tasklet_unlock(t);
 				continue;
 			}

Re: [PATCH] softirq: Be more verbose on t->state BUG()

[Eugeniu Rosca]

Hello Thomas,

On Tue, Mar 16, 2021 at 03:31:50PM +0100, Thomas Gleixner wrote:
> On Mon, Mar 15 2021 at 16:44, Eugeniu Rosca wrote:
> > From: Dirk Behme <dirk.behme@de.bosch.com>
> >
> > In case this BUG() is hit, it helps debugging a lot to get an idea
> > what tasklet is the root cause. So, be slightly more verbose here.
> >
> > Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
> > Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
> > ---
> >  kernel/softirq.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/softirq.c b/kernel/softirq.c
> > index 9908ec4a9bfe..a6b602ad48d6 100644
> > --- a/kernel/softirq.c
> > +++ b/kernel/softirq.c
> > @@ -550,9 +550,13 @@ static void tasklet_action_common(struct softirq_action *a,
> >  
> >  		if (tasklet_trylock(t)) {
> >  			if (!atomic_read(&t->count)) {
> > -				if (!test_and_clear_bit(TASKLET_STATE_SCHED,
> > -							&t->state))
> > +				if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state)) {
> > +					if (t->use_callback)
> > +						pr_emerg("tasklet failed, cb: %pS\n", t->callback);
> > +					else
> > +						pr_emerg("tasklet failed, func: %pS\n", t->func);
> >  					BUG();
> > +				}
> >  				if (t->use_callback)
> >  					t->callback(t);
> >  				else
> 
> This belongs into unreadable land and actually the BUG() should just be
> replaced by a WARN_ONCE(). Something like the below. Hmm?

Many thanks for the quick and constructive reply.

If no other comments in the next days, I will resubmit your proposal as
v2, marked with 'Suggested-by: Thomas Gleixner <tglx@linutronix.de>'.

Alternatively, feel free to author the patch and submit it with us in Cc.

Thanks again.

-- 
Best regards,
Eugeniu Rosca

Re: [PATCH] softirq: Be more verbose on t->state BUG()

[Thomas Gleixner]

On Tue, Mar 16 2021 at 16:10, Eugeniu Rosca wrote:
> If no other comments in the next days, I will resubmit your proposal as
> v2, marked with 'Suggested-by: Thomas Gleixner <tglx@linutronix.de>'.
>
> Alternatively, feel free to author the patch and submit it with us in Cc.

Just send a v2 please

Re: [PATCH] softirq: Be more verbose on t->state BUG()

[Eugeniu Rosca]

Hello Thomas,

On Tue, Mar 16, 2021 at 06:13:12PM +0100, Thomas Gleixner wrote:
> On Tue, Mar 16 2021 at 16:10, Eugeniu Rosca wrote:
> > If no other comments in the next days, I will resubmit your proposal as
> > v2, marked with 'Suggested-by: Thomas Gleixner <tglx@linutronix.de>'.
> >
> > Alternatively, feel free to author the patch and submit it with us in Cc.
> 
> Just send a v2 please

https://lore.kernel.org/lkml/20210317102012.32399-1-erosca@de.adit-jv.com/
("[PATCH v2] softirq: s/BUG/WARN_ONCE/ on tasklet SCHED state not set")

-- 
Best regards,
Eugeniu Rosca