linux-kernel - [PATCH rcu 10/11] rcu_sync: Fix comment to properly reflect rcu_sync

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Message-Id: <20220418225359.3945217-10-paulmck@kernel.org>
Date:   Mon, 18 Apr 2022 15:53:58 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, David Vernet <void@...ifault.com>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 10/11] rcu_sync: Fix comment to properly reflect rcu_sync_exit() behavior

From: David Vernet <void@...ifault.com>

The rcu_sync_enter() function is used by updaters to force RCU readers
(e.g. percpu-rwsem) to use their slow paths during an update.  This is
accomplished by setting the ->gp_state of the rcu_sync structure to
GP_ENTER.  In the case of percpu-rwsem, the readers' slow path waits on
a semaphore instead of just incrementing a reader count.  Each updater
invokes the rcu_sync_exit() function to signal to readers that they
may again take their fastpaths.  The rcu_sync_exit() function sets the
->gp_state of the rcu_sync structure to GP_EXIT, and if all goes well,
after a grace period the ->gp_state reverts back to GP_IDLE.

Unfortunately, the rcu_sync_enter() function currently has a comment
incorrectly stating that rcu_sync_exit() (by an updater) will re-enable
reader "slowpaths".  This patch changes the comment to state that this
function re-enables reader fastpaths.

Signed-off-by: David Vernet <void@...ifault.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 kernel/rcu/sync.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
index 33d896d85902..5cefc702158f 100644
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -111,7 +111,7 @@ static void rcu_sync_func(struct rcu_head *rhp)
  * a slowpath during the update.  After this function returns, all
  * subsequent calls to rcu_sync_is_idle() will return false, which
  * tells readers to stay off their fastpaths.  A later call to
- * rcu_sync_exit() re-enables reader slowpaths.
+ * rcu_sync_exit() re-enables reader fastpaths.
  *
  * When called in isolation, rcu_sync_enter() must wait for a grace
  * period, however, closely spaced calls to rcu_sync_enter() can
-- 
2.31.1.189.g2e36527f23