Re: [PATCH 1/2] SRCU: report out-of-memory errors

["Paul E. McKenney" <paulmck@us.ibm.com>]

On Wed, Aug 02, 2006 at 04:38:28PM -0400, Alan Stern wrote:
> Currently the init_srcu_struct() routine has no way to report 
> out-of-memory errors.  This patch (as761) makes it return -ENOMEM when the 
> per-cpu data allocation fails.
> 
> The patch also makes srcu_init_notifier_head() report a BUG if a notifier
> head can't be initialized.  Perhaps it should return -ENOMEM instead, but
> in the most likely cases where this might occur I don't think any recovery
> is possible.  Notifier chains generally are not created dynamically.

Acked-by: Paul E. McKenney <paulmck@us.ibm.com>

> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> 
> ---
> 
> Paul, I trust you will agree with the changes this makes to the SRCU code.

Indeed I do...  Good catch!!!

							Thanx, Paul

> The second part of this patch series will convert the cpufreq transition 
> notifier chain to use SRCU, with the initialization occuring in a 
> core_initcall routine.  Although I haven't actually tried it, it seems 
> very likely that an attempt to use the notifier chain before it has been 
> initialized will cause a memory-address fault.
> 
> Alan Stern
> 
> 
> Index: 2.6.18-rc2-mm1/kernel/sys.c
> ===================================================================
> --- 2.6.18-rc2-mm1.orig/kernel/sys.c
> +++ 2.6.18-rc2-mm1/kernel/sys.c
> @@ -516,7 +516,7 @@ EXPORT_SYMBOL_GPL(srcu_notifier_call_cha
>  void srcu_init_notifier_head(struct srcu_notifier_head *nh)
>  {
>  	mutex_init(&nh->mutex);
> -	init_srcu_struct(&nh->srcu);
> +	BUG_ON(init_srcu_struct(&nh->srcu) < 0);
>  	nh->head = NULL;
>  }
>  
> Index: 2.6.18-rc2-mm1/kernel/srcu.c
> ===================================================================
> --- 2.6.18-rc2-mm1.orig/kernel/srcu.c
> +++ 2.6.18-rc2-mm1/kernel/srcu.c
> @@ -42,11 +42,12 @@
>   * to any other function.  Each srcu_struct represents a separate domain
>   * of SRCU protection.
>   */
> -void init_srcu_struct(struct srcu_struct *sp)
> +int init_srcu_struct(struct srcu_struct *sp)
>  {
>  	sp->completed = 0;
> -	sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
>  	mutex_init(&sp->mutex);
> +	sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
> +	return (sp->per_cpu_ref ? 0 : -ENOMEM);
>  }
>  
>  /*
> Index: 2.6.18-rc2-mm1/include/linux/srcu.h
> ===================================================================
> --- 2.6.18-rc2-mm1.orig/include/linux/srcu.h
> +++ 2.6.18-rc2-mm1/include/linux/srcu.h
> @@ -43,7 +43,7 @@ struct srcu_struct {
>  #define srcu_barrier()
>  #endif /* #else #ifndef CONFIG_PREEMPT */
>  
> -void init_srcu_struct(struct srcu_struct *sp);
> +int init_srcu_struct(struct srcu_struct *sp);
>  void cleanup_srcu_struct(struct srcu_struct *sp);
>  int srcu_read_lock(struct srcu_struct *sp);
>  void srcu_read_unlock(struct srcu_struct *sp, int idx);
>