The MM-notifier code currently dynamically initializes the srcu_struct named "srcu" at subsys_initcall() time, and includes a BUG_ON() to check this initialization in do_mmu_notifier_register(). Unfortunately, there is no foolproof way to verify that an srcu_struct has been initialized, given the possibility of an srcu_struct being allocated on the stack or on the heap. This means that creating an srcu_struct_is_initialized() function is not a reasonable course of action. Nor is peppering do_mmu_notifier_register() with SRCU-specific #ifdefs an attractive alternative.
This commit therefore uses DEFINE_STATIC_SRCU() to initialize this srcu_struct at compile time, thus eliminating both the subsys_initcall()-time initialization and the runtime BUG_ON(). Signed-off-by: Paul E. McKenney <[email protected]> Cc: <[email protected]> Cc: Andrew Morton <[email protected] Cc: Ingo Molnar <[email protected]> Cc: Michal Hocko <[email protected]> Cc: "Peter Zijlstra (Intel)" <[email protected]> Cc: Vegard Nossum <[email protected]> --- mm/mmu_notifier.c | 14 +------------- 1 file changed, 1 insertion(+), 13 deletions(-) diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index a7652acd2ab9..54ca54562928 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -21,7 +21,7 @@ #include <linux/slab.h> /* global SRCU for all MMs */ -static struct srcu_struct srcu; +DEFINE_STATIC_SRCU(srcu); /* * This function allows mmu_notifier::release callback to delay a call to @@ -252,12 +252,6 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn, BUG_ON(atomic_read(&mm->mm_users) <= 0); - /* - * Verify that mmu_notifier_init() already run and the global srcu is - * initialized. - */ - BUG_ON(!srcu.per_cpu_ref); - ret = -ENOMEM; mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL); if (unlikely(!mmu_notifier_mm)) @@ -406,9 +400,3 @@ void mmu_notifier_unregister_no_release(struct mmu_notifier *mn, mmdrop(mm); } EXPORT_SYMBOL_GPL(mmu_notifier_unregister_no_release); - -static int __init mmu_notifier_init(void) -{ - return init_srcu_struct(&srcu); -} -subsys_initcall(mmu_notifier_init); -- 2.5.2
