On 9/2/20 1:56 AM, [email protected] wrote: > On Tue, Sep 01, 2020 at 08:51:46PM -0700, Guenter Roeck wrote: > >> [ 27.056457] include/trace/events/lock.h:13 suspicious >> rcu_dereference_check() usage! > >> [ 27.057006] Hardware name: Generic OMAP3-GP (Flattened Device Tree) >> [ 27.057098] [<c03125b4>] (unwind_backtrace) from [<c030c32c>] >> (show_stack+0x10/0x14) >> [ 27.057189] [<c030c32c>] (show_stack) from [<c08e7a4c>] >> (dump_stack+0xd8/0xf8) >> [ 27.057312] [<c08e7a4c>] (dump_stack) from [<c03b04bc>] >> (lock_acquire+0x4d8/0x4dc) >> [ 27.057464] [<c03b04bc>] (lock_acquire) from [<c12457e8>] >> (_raw_spin_lock_irqsave+0x58/0x74) >> [ 27.057617] [<c12457e8>] (_raw_spin_lock_irqsave) from [<c0338198>] >> (pwrdm_lock+0x10/0x18) >> [ 27.057739] [<c0338198>] (pwrdm_lock) from [<c033a214>] >> (clkdm_deny_idle+0x10/0x24) >> [ 27.057891] [<c033a214>] (clkdm_deny_idle) from [<c0332e10>] >> (omap3_enter_idle_bm+0xd4/0x1b8) >> [ 27.058044] [<c0332e10>] (omap3_enter_idle_bm) from [<c0f740d4>] >> (cpuidle_enter_state+0x16c/0x620) > > ARM cpuidle is a trainwreck :/ > > So it looks like we have: > > - clkdm_ > - pwrdm_ > - cpu_pm_ > - pm_runtime_ > > In that approximate order, and then there's the coupled idle muck. > Sometimes cpuidle core calls cpu_pm_*(), but mostly it's sprinkled > around in drivers. > > How about we unconditionally kill tracing when RCU is idle? Yes this is > a hack, and we really should turn it into a WARN in due time. > > The thing is, we're shutting down clock/power domains and god knows > what, the CPU is in a crap state, we'll not take interrupts, but tracing > must happen! Hell no. > > Let's make the rule that if you want something traced, you get to pull > it out of the cpuidle driver and stick it in the generic code with a > CPUIDLE_FLAG, before rcu_idle_enter(). > > Totally untested patch below.. >
Unfortunately, that patch does not make a difference; I still see the same tracebacks with it applied. Guenter > --- > > diff --git a/include/linux/preempt.h b/include/linux/preempt.h > index 7d9c1c0e149c..878bac893e41 100644 > --- a/include/linux/preempt.h > +++ b/include/linux/preempt.h > @@ -27,17 +27,20 @@ > * SOFTIRQ_MASK: 0x0000ff00 > * HARDIRQ_MASK: 0x000f0000 > * NMI_MASK: 0x00f00000 > + * RCUIDLE_MASK: 0x01000000 > * PREEMPT_NEED_RESCHED: 0x80000000 > */ > #define PREEMPT_BITS 8 > #define SOFTIRQ_BITS 8 > #define HARDIRQ_BITS 4 > #define NMI_BITS 4 > +#define RCUIDLE_BITS 1 > > #define PREEMPT_SHIFT 0 > #define SOFTIRQ_SHIFT (PREEMPT_SHIFT + PREEMPT_BITS) > #define HARDIRQ_SHIFT (SOFTIRQ_SHIFT + SOFTIRQ_BITS) > #define NMI_SHIFT (HARDIRQ_SHIFT + HARDIRQ_BITS) > +#define RCUIDLE_SHIFT (NMI_SHIFT + NMI_BITS) > > #define __IRQ_MASK(x) ((1UL << (x))-1) > > @@ -45,11 +48,13 @@ > #define SOFTIRQ_MASK (__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT) > #define HARDIRQ_MASK (__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT) > #define NMI_MASK (__IRQ_MASK(NMI_BITS) << NMI_SHIFT) > +#define RCUIDLE_MASK (__IRQ_MASK(RCUIDLE_BITS) << RCUIDLE_SHIFT) > > #define PREEMPT_OFFSET (1UL << PREEMPT_SHIFT) > #define SOFTIRQ_OFFSET (1UL << SOFTIRQ_SHIFT) > #define HARDIRQ_OFFSET (1UL << HARDIRQ_SHIFT) > #define NMI_OFFSET (1UL << NMI_SHIFT) > +#define RCUIDLE_OFFSET (1UL << RCUIDLE_SHIFT) > > #define SOFTIRQ_DISABLE_OFFSET (2 * SOFTIRQ_OFFSET) > > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h > index 598fec9f9dbf..997472c662c4 100644 > --- a/include/linux/tracepoint.h > +++ b/include/linux/tracepoint.h > @@ -164,7 +164,7 @@ static inline struct tracepoint > *tracepoint_ptr_deref(tracepoint_ptr_t *p) > void *__data; \ > int __maybe_unused __idx = 0; \ > \ > - if (!(cond)) \ > + if (!(cond) || (preempt_count() & RCUIDLE_MASK)) \ > return; \ > \ > /* srcu can't be used from NMI */ \ > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 8ce77d9ac716..ad9fb4f12c63 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -269,6 +269,8 @@ static noinstr void rcu_dynticks_eqs_enter(void) > /* Better not have special action (TLB flush) pending! */ > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && > (seq & RCU_DYNTICK_CTRL_MASK)); > + > + __preempt_count_add(RCUIDLE_OFFSET); > } > > /* > @@ -281,6 +283,8 @@ static noinstr void rcu_dynticks_eqs_exit(void) > struct rcu_data *rdp = this_cpu_ptr(&rcu_data); > int seq; > > + __preempt_count_sub(RCUIDLE_OFFSET); > + > /* > * CPUs seeing atomic_add_return() must see prior idle sojourns, > * and we also must force ordering with the next RCU read-side >
