Re: [Adeos-main] [PATCH] Detect leaking stalls of topmost domain - v2

[Philippe Gerum <rpm@xenomai.org>]

Jan Kiszka wrote:
> Here comes an improved version of my debugging helper for leaking
> top-most domain stalls. This version is now also NMI-safe, no longer
> causing false positives from this context.
>

Applied, thanks.

> The instrumentation can detect infamous bug pattern like this:
> 
> function()
> {
> 	stall_topmost_domain();
> 	...
> 	if (condition)
> 		return;
> 	...
> 	unstall_topmost_domain();
> }
> 
> The result is often a locked-up system, specifically the root domain no
> longer receives IRQs. Unless you find the bug quickly by code
> inspection, debugging/instrumenting can take quite some time.
> 
> Also, this patch can help with these patterns:
> 
> 	stall_topmost_domain();
> 	...
> 	blocking_or_rescheduling_in_lowprio_domain();
> 	...
> 	unstall_topmost_domain();
> 
> One example of this was just fixed in Xenomai's cleanup code.
> 
> To catch such issues earlier, I therefore propose the following
> extension of ipipe_check_context. It is based on the assumption that the
> topmost domain should never be stalled when lower domains execute that
> check. This specifically takes care of not breaking Xenomai's IRQ shield
> (a mid-prio domain that intentionally blocks Linux IRQs).
> 
> 
> ---
>  include/linux/hardirq.h      |   19 +++++++++++++++++--
>  include/linux/ipipe.h        |   20 ++++++++++++++++++++
>  include/linux/ipipe_percpu.h |    1 +
>  kernel/ipipe/core.c          |   21 ++++++++++++++++-----
>  4 files changed, 54 insertions(+), 7 deletions(-)
> 
> Index: b/kernel/ipipe/core.c
> ===================================================================
> --- a/kernel/ipipe/core.c
> +++ b/kernel/ipipe/core.c
> @@ -1561,13 +1561,16 @@ void __init ipipe_init_proc(void)
>  #ifdef CONFIG_IPIPE_DEBUG_CONTEXT
>  
>  DEFINE_PER_CPU(int, ipipe_percpu_context_check) = { 1 };
> +DEFINE_PER_CPU(int, ipipe_saved_context_check_state);
>  
>  void ipipe_check_context(struct ipipe_domain *border_ipd)
>  {
>  	/* Note: We don't make the per_cpu access atomic. We assume that code
>  	   which temporarily disables the check does this in atomic context
>  	   only. */
> -	if (likely(ipipe_current_domain->priority <= border_ipd->priority) ||
> +	if (likely(ipipe_current_domain->priority <= border_ipd->priority &&
> +		   !test_bit(IPIPE_STALL_FLAG,
> +			     &ipipe_head_cpudom_var(status))) ||
>  	    !per_cpu(ipipe_percpu_context_check, ipipe_processor_id()))
>  		return;
>  
> @@ -1575,10 +1578,18 @@ void ipipe_check_context(struct ipipe_do
>  
>  	ipipe_trace_panic_freeze();
>  	ipipe_set_printk_sync(ipipe_current_domain);
> -	printk(KERN_ERR "I-pipe: Detected illicit call from domain '%s'\n"
> -	       KERN_ERR "        into a service reserved for domain '%s' and "
> -			"below.\n",
> -	       ipipe_current_domain->name, border_ipd->name);
> +
> +	if (ipipe_current_domain->priority > border_ipd->priority)
> +		printk(KERN_ERR "I-pipe: Detected illicit call from domain "
> +				"'%s'\n"
> +		       KERN_ERR "        into a service reserved for domain "
> +				"'%s' and below.\n",
> +		       ipipe_current_domain->name, border_ipd->name);
> +	else
> +		printk(KERN_ERR "I-pipe: Detected stalled topmost domain, "
> +				"probably caused by a bug.\n"
> +				"        A critical section may have been "
> +				"left unterminated.\n");
>  	dump_stack();
>  	ipipe_trace_panic_dump();
>  }
> Index: b/include/linux/hardirq.h
> ===================================================================
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -161,7 +161,22 @@ extern void irq_enter(void);
>   */
>  extern void irq_exit(void);
>  
> -#define nmi_enter()		do { if (ipipe_root_domain_p) { lockdep_off(); __irq_enter(); } } while (0)
> -#define nmi_exit()		do { if (ipipe_root_domain_p) { __irq_exit(); lockdep_on(); } } while (0)
> +#define nmi_enter() 					\
> +	do {						\
> +		ipipe_nmi_enter();			\
> +		if (ipipe_root_domain_p) {		\
> +			lockdep_off();			\
> +			__irq_enter();			\
> +		}					\
> +	} while (0)
> +
> +#define nmi_exit()					\
> +	do {						\
> +		if (ipipe_root_domain_p) {		\
> +			__irq_exit();			\
> +			lockdep_on();			\
> +		}					\
> +		ipipe_nmi_exit();			\
> +	} while (0)
>  
>  #endif /* LINUX_HARDIRQ_H */
> Index: b/include/linux/ipipe.h
> ===================================================================
> --- a/include/linux/ipipe.h
> +++ b/include/linux/ipipe.h
> @@ -566,6 +566,22 @@ static inline void ipipe_context_check_o
>  		per_cpu(ipipe_percpu_context_check, cpu) = 0;
>  }
>  
> +static inline void ipipe_nmi_enter(void)
> +{
> +	int cpu = ipipe_processor_id();
> +
> +	per_cpu(ipipe_saved_context_check_state, cpu) =
> +		ipipe_disable_context_check(cpu);
> +}
> +
> +static inline void ipipe_nmi_exit(void)
> +{
> +	int cpu = ipipe_processor_id();
> +
> +	ipipe_restore_context_check
> +		(cpu, per_cpu(ipipe_saved_context_check_state, cpu));
> +}
> +
>  #else	/* !CONFIG_IPIPE_DEBUG_CONTEXT */
>  
>  static inline int ipipe_disable_context_check(int cpu)
> @@ -577,6 +593,10 @@ static inline void ipipe_restore_context
>  
>  static inline void ipipe_context_check_off(void) { }
>  
> +static inline void ipipe_nmi_enter(void) { }
> +
> +static inline void ipipe_nmi_exit(void) { }
> +
>  #endif	/* !CONFIG_IPIPE_DEBUG_CONTEXT */
>  
>  #endif	/* !__LINUX_IPIPE_H */
> Index: b/include/linux/ipipe_percpu.h
> ===================================================================
> --- a/include/linux/ipipe_percpu.h
> +++ b/include/linux/ipipe_percpu.h
> @@ -58,6 +58,7 @@ DECLARE_PER_CPU(struct ipipe_domain *, i
>  
>  #ifdef CONFIG_IPIPE_DEBUG_CONTEXT
>  DECLARE_PER_CPU(int, ipipe_percpu_context_check);
> +DECLARE_PER_CPU(int, ipipe_saved_context_check_state);
>  #endif
>  
>  #define ipipe_percpu(var, cpu)		per_cpu(var, cpu)
> 
> 
> 
> ------------------------------------------------------------------------
> 
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-- 
Philippe.