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

From: Alan Stern
Date: Wed Aug 02 2006 - 16:36:26 EST

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.

Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>


Paul, I trust you will agree with the changes this makes to the SRCU code.

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)
- 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);
+ 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);

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