[PATCH] mm/mmu_notifier: rename mmu_notifier_synchronize() to <...>_barrier()

* [PATCH] mm/mmu_notifier: rename mmu_notifier_synchronize() to <...>_barrier()
@ 2018-11-05 19:29 Sean Christopherson
  2018-11-05 20:18 ` Andrew Morton
  0 siblings, 1 reply; 6+ messages in thread
From: Sean Christopherson @ 2018-11-05 19:29 UTC (permalink / raw)
  To: Andrew Morton, linux-mm
  Cc: linux-kernel, Peter Zijlstra, Jérôme Glisse, Oded Gabbay

...and update its comment to explicitly reference its association with
mmu_notifier_call_srcu().

Contrary to its name, mmu_notifier_synchronize() does not synchronize
the notifier's SRCU instance, but rather waits for RCU callbacks to
finished, i.e. it invokes rcu_barrier().  The RCU documentation is
quite clear on this matter, explicitly calling out that rcu_barrier()
does not imply synchronize_rcu().  The misnomer could lean an unwary
developer to incorrectly assume that mmu_notifier_synchronize() can
be used in conjunction with mmu_notifier_unregister_no_release() to
implement a variation of mmu_notifier_unregister() that synchronizes
SRCU without invoking ->release.  A Documentation-allergic and hasty
developer could be further confused by the fact that rcu_barrier() is
indeed a pass-through to synchronize_rcu()... in tiny SRCU.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 mm/mmu_notifier.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 5119ff846769..46ebea6483bf 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -35,12 +35,12 @@ void mmu_notifier_call_srcu(struct rcu_head *rcu,
 }
 EXPORT_SYMBOL_GPL(mmu_notifier_call_srcu);
 
-void mmu_notifier_synchronize(void)
+void mmu_notifier_barrier(void)
 {
-	/* Wait for any running method to finish. */
+	/* Wait for any running RCU callbacks (see above) to finish. */
 	srcu_barrier(&srcu);
 }
-EXPORT_SYMBOL_GPL(mmu_notifier_synchronize);
+EXPORT_SYMBOL_GPL(mmu_notifier_barrier);
 
 /*
  * This function can't run concurrently against mmu_notifier_register
-- 
2.19.1


^ permalink raw reply related	[flat|nested] 6+ messages in thread