Messages in this thread | | | Date | Thu, 30 Jun 2022 18:37:04 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] sched: fix rq lock recursion issue |
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On Fri, Jun 24, 2022 at 12:42:40AM -0700, Satya Durga Srinivasu Prabhala wrote: > Below recursion is observed in a rare scenario where __schedule() > takes rq lock, at around same time task's affinity is being changed, > bpf function for tracing sched_switch calls migrate_enabled(), > checks for affinity change (cpus_ptr != cpus_mask) lands into > __set_cpus_allowed_ptr which tries acquire rq lock and causing the > recursion bug. > > Fix the issue by switching to preempt_enable/disable() for non-RT > Kernels. > > -010 |spin_bug(lock = ???, msg = ???) > -011 |debug_spin_lock_before(inline) > -011 |do_raw_spin_lock(lock = 0xFFFFFF89323BB600) > -012 |_raw_spin_lock(inline) > -012 |raw_spin_rq_lock_nested(inline) > -012 |raw_spin_rq_lock(inline) > -012 |task_rq_lock(p = 0xFFFFFF88CFF1DA00, rf = 0xFFFFFFC03707BBE8) > -013 |__set_cpus_allowed_ptr(inline) > -013 |migrate_enable() > -014 |trace_call_bpf(call = ?, ctx = 0xFFFFFFFDEF954600) > -015 |perf_trace_run_bpf_submit(inline) > -015 |perf_trace_sched_switch(__data = 0xFFFFFFE82CF0BCB8, preempt = FALSE, prev = ?, next = ?) > -016 |__traceiter_sched_switch(inline) > -016 |trace_sched_switch(inline)
trace_sched_switch() disables preemption.
So how is this a fix?
-- Steve
> -016 |__schedule(sched_mode = ?) > -017 |schedule() > -018 |arch_local_save_flags(inline) > -018 |arch_irqs_disabled(inline) > -018 |__raw_spin_lock_irq(inline) > -018 |_raw_spin_lock_irq(inline) > -018 |worker_thread(__worker = 0xFFFFFF88CE251300) > -019 |kthread(_create = 0xFFFFFF88730A5A80) > -020 |ret_from_fork(asm) > > Signed-off-by: Satya Durga Srinivasu Prabhala <quic_satyap@quicinc.com> > --- > kernel/sched/core.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index bfa7452ca92e..e254e9227341 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2223,6 +2223,7 @@ static void migrate_disable_switch(struct rq *rq, struct task_struct *p) > > void migrate_disable(void) > { > +#ifdef CONFIG_PREEMPT_RT > struct task_struct *p = current; > > if (p->migration_disabled) { > @@ -2234,11 +2235,15 @@ void migrate_disable(void) > this_rq()->nr_pinned++; > p->migration_disabled = 1; > preempt_enable(); > +#else > + preempt_disable(); > +#endif > } > EXPORT_SYMBOL_GPL(migrate_disable); > > void migrate_enable(void) > { > +#ifdef CONFIG_PREEMPT_RT > struct task_struct *p = current; > > if (p->migration_disabled > 1) { > @@ -2265,6 +2270,9 @@ void migrate_enable(void) > p->migration_disabled = 0; > this_rq()->nr_pinned--; > preempt_enable(); > +#else > + preempt_enable(); > +#endif > } > EXPORT_SYMBOL_GPL(migrate_enable); > > -- > 2.36.1
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