Messages in this thread | | | From | Satya Durga Srinivasu Prabhala <> | Subject | Re: [PATCH] sched: fix rq lock recursion issue | Date | Mon, 4 Jul 2022 19:06:56 -0700 |
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On 6/30/22 2:53 PM, Qais Yousef wrote: > Hi Satya > > On 06/24/22 00:42, 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. > Interesting bug. Thanks for the report. Unfortunately I can't see this being > a fix as it just limits the bug visibility to PREEMPT_RT kernels, but won't fix > anything, no? ie: Kernels compiled with PREEMPT_RT will still hit this failure. Thanks for taking a look. That's right. > I'm curious how the race with set affinity is happening. I would have thought > user space would get blocked as __schedule() will hold the rq lock. > > Do you have more details on that? I'm still trying to figure out how we even end with up such a race. No easy way repro the issue, I'm checking internally with some debug logs. > > Thanks > > -- > Qais Yousef > >> -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) >> -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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