Commit f1efe84d authored Mar 29, 2022 by David Vernet Committed by Paul E. McKenney Apr 20, 2022

rcu_sync: Fix comment to properly reflect rcu_sync_exit() behavior



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@manifault.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

parent 88ca472f

kernel/rcu/sync.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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