linux-kernel - [PATCH] mm/mmu_notifier: rename mmu_notifier_synchronize() to <...>

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Message-Id: <20181105192955.26305-1-sean.j.christopherson@intel.com>
Date:   Mon,  5 Nov 2018 11:29:55 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Oded Gabbay <oded.gabbay@....com>
Subject: [PATCH] mm/mmu_notifier: rename mmu_notifier_synchronize() to <...>_barrier()

...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@...el.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