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From 7be707833bb35c295eb702d13cf73ac9390e4b31 Mon Sep 17 00:00:00 2001
From: Arjan van de Ven <arjan@linux.intel.com>
Date: Wed, 11 Feb 2015 16:25:16 -0600
Subject: [PATCH 103/114] sysrq: skip synchronize_rcu() if there is no old op
synchronize_rcu() is expensive. Currently it is called as part of the sysrq
registration/unregistration, which happens during boot several times.
Now, the reason for the synchronize_rcu() is to allow an old registered
operation to expire properly... which is pointless if the old operation
is NULL...
So we can save the common case of the old operation being NULL a lot of time
by just checking for non-NULL prior to the synchronize_rcu()
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
---
drivers/tty/sysrq.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 701c085bb19b..c60c7ba57ad9 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -1065,8 +1065,10 @@ static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
* A concurrent __handle_sysrq either got the old op or the new op.
* Wait for it to go away before returning, so the code for an old
* op is not freed (eg. on module unload) while it is in use.
+ * This is only relevant if the old op is not NULL of course.
*/
- synchronize_rcu();
+ if (remove_op_p)
+ synchronize_rcu();
return retval;
}
--
2.11.1
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