Messages in this thread | | | Subject | Re: [PATCH v2] sched/fair: WARN and refuse to set buddy when !se->on_rq | From | Konstantin Khlebnikov <> | Date | Tue, 20 Jun 2017 10:41:38 +0300 |
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On 19.06.2017 17:05, Daniel Axtens wrote: > Hi Konstantin and Peter, > > Just checking if this version was OK with you - I hadn't heard anything > and I noticed it's not in -next so I just wanted to check to see if > there were any other changes you wanted.
Looks good for me. Exactly that debug helped me alot at that time.
> > Regards, > Daniel > > > Daniel Axtens <dja@axtens.net> writes: > >> 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. >> >> v2: use SCHED_WARN_ON to restrict when the test is run. This is a >> macro for WARN_ON_ONCE, which is convenient. >> --- >> 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..44b94cfe02cb 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 (SCHED_WARN_ON(!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 (SCHED_WARN_ON(!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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