Messages in this thread | | | From | Daniel Axtens <> | Subject | Re: [PATCH] sched/fair: WARN and refuse to set buddy when !se->on_rq | Date | Tue, 09 May 2017 11:47:17 +1000 |
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Konstantin Khlebnikov <koct9i@gmail.com> writes:
> On Mon, May 8, 2017 at 10:22 PM, Daniel Axtens <dja@axtens.net> wrote: >> If we set a next or last buddy for a se that is not on_rq, we will >> end up taking a NULL pointer dereference in wakeup_preempt_entity >> via pick_next_task_fair. >> >> Detect when we would be about to do that, throw a warning and >> then refuse to actually set it. >> >> This has been suggested at least twice[0][1]: just do it. >> >> [0] https://marc.info/?l=linux-kernel&m=146651668921468&w=2 >> [1] https://lkml.org/lkml/2016/6/16/663 >> >> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> >> Cc: Ben Segall <bsegall@google.com> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Cc: Thomas Gleixner <tglx@linutronix.de> >> Signed-off-by: Daniel Axtens <dja@axtens.net> >> >> --- >> >> I recently had to debug a problem with these (we hadn't backported >> Konstantin's patches in this area) and this would have saved a lot >> of time/pain. > > Yep, this is worth debug. But I think it should be under compile-time > config option. > Something like CONFIG_DEBUG_VM which enables VM_BUG_ON and VM_WARN_ON.
OK, will respin.
Regards, Daniel
> >> --- >> kernel/sched/fair.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index d71109321841..9b988815b4ad 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -6168,8 +6168,11 @@ static void set_last_buddy(struct sched_entity *se) >> if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE)) >> return; >> >> - for_each_sched_entity(se) >> + for_each_sched_entity(se) { >> + if (WARN_ON_ONCE(!se->on_rq)) >> + return; >> cfs_rq_of(se)->last = se; >> + } >> } >> >> static void set_next_buddy(struct sched_entity *se) >> @@ -6177,8 +6180,11 @@ static void set_next_buddy(struct sched_entity *se) >> if (entity_is_task(se) && unlikely(task_of(se)->policy == SCHED_IDLE)) >> return; >> >> - for_each_sched_entity(se) >> + for_each_sched_entity(se) { >> + if (WARN_ON_ONCE(!se->on_rq)) >> + return; >> cfs_rq_of(se)->next = se; >> + } >> } >> >> static void set_skip_buddy(struct sched_entity *se) >> -- >> 2.11.0 >>
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