2022-11-15 20:29:41

by Thomas Gleixner

Subject: [patch 05/15] timers: Replace BUG_ON()s

The timer code still has a few BUG_ON()s left which are crashing the kernel
in situations where it still can recover or simply refuse to take an
action.

Remove the one in the hotplug callback which checks for the CPU being
offline. If that happens then the whole hotplug machinery will explode in
colourful ways.

Replace the rest with WARN_ON_ONCE() and conditional returns where
appropriate.

Signed-off-by: Thomas Gleixner <[email protected]>
---
kernel/time/timer.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1193,7 +1193,8 @@ EXPORT_SYMBOL(timer_reduce);
*/
void add_timer(struct timer_list *timer)
{
- BUG_ON(timer_pending(timer));
+ if (WARN_ON_ONCE(timer_pending(timer)))
+ return;
__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
}
EXPORT_SYMBOL(add_timer);
@@ -1210,7 +1211,8 @@ void add_timer_on(struct timer_list *tim
struct timer_base *new_base, *base;
unsigned long flags;

- BUG_ON(timer_pending(timer) || !timer->function);
+ if (WARN_ON_ONCE(timer_pending(timer) || !timer->function))
+ return;

new_base = get_timer_cpu_base(timer->flags, cpu);

@@ -2017,8 +2019,6 @@ int timers_dead_cpu(unsigned int cpu)
struct timer_base *new_base;
int b, i;

- BUG_ON(cpu_online(cpu));
-
for (b = 0; b < NR_BASES; b++) {
old_base = per_cpu_ptr(&timer_bases[b], cpu);
new_base = get_cpu_ptr(&timer_bases[b]);
@@ -2035,7 +2035,8 @@ int timers_dead_cpu(unsigned int cpu)
*/
forward_timer_base(new_base);

- BUG_ON(old_base->running_timer);
+ WARN_ON_ONCE(old_base->running_timer);
+ old_base->running_timer = NULL;

for (i = 0; i < WHEEL_SIZE; i++)
migrate_timer_list(new_base, old_base->vectors + i);

2022-11-21 20:27:40

by Steven Rostedt

Subject: Re: [patch 05/15] timers: Replace BUG_ON()s

On Tue, 15 Nov 2022 21:28:41 +0100 (CET)
Thomas Gleixner <[email protected]> wrote:

> The timer code still has a few BUG_ON()s left which are crashing the kernel
> in situations where it still can recover or simply refuse to take an
> action.
>
> Remove the one in the hotplug callback which checks for the CPU being
> offline. If that happens then the whole hotplug machinery will explode in
> colourful ways.
>
> Replace the rest with WARN_ON_ONCE() and conditional returns where
> appropriate.
>
> Signed-off-by: Thomas Gleixner <[email protected]>
> ---
> kernel/time/timer.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1193,7 +1193,8 @@ EXPORT_SYMBOL(timer_reduce);
> */
> void add_timer(struct timer_list *timer)
> {
> - BUG_ON(timer_pending(timer));
> + if (WARN_ON_ONCE(timer_pending(timer)))
> + return;
> __mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
> }
> EXPORT_SYMBOL(add_timer);
> @@ -1210,7 +1211,8 @@ void add_timer_on(struct timer_list *tim
> struct timer_base *new_base, *base;
> unsigned long flags;
>
> - BUG_ON(timer_pending(timer) || !timer->function);
> + if (WARN_ON_ONCE(timer_pending(timer) || !timer->function))
> + return;
>
> new_base = get_timer_cpu_base(timer->flags, cpu);
>

I wonder if this patch should be split up into two patches, as the above is
trivial and the below is a bit more "complex". Although it's probably moot
as none of these should ever trigger.

> @@ -2017,8 +2019,6 @@ int timers_dead_cpu(unsigned int cpu)
> struct timer_base *new_base;
> int b, i;
>
> - BUG_ON(cpu_online(cpu));
> -
> for (b = 0; b < NR_BASES; b++) {
> old_base = per_cpu_ptr(&timer_bases[b], cpu);
> new_base = get_cpu_ptr(&timer_bases[b]);
> @@ -2035,7 +2035,8 @@ int timers_dead_cpu(unsigned int cpu)
> */
> forward_timer_base(new_base);
>
> - BUG_ON(old_base->running_timer);
> + WARN_ON_ONCE(old_base->running_timer);
> + old_base->running_timer = NULL;

I guess interesting things could happen if running_timer was not NULL, but
again, WARN_ON_ONCE() should never be triggered in a correctly running
kernel.

Reviewed-by: Steven Rostedt (Google) <[email protected]>

-- Steve

>
> for (i = 0; i < WHEEL_SIZE; i++)
> migrate_timer_list(new_base, old_base->vectors + i);