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From: Mateusz Guzik <mjg@FreeBSD.org>
Date: Wed, 10 Aug 2016 15:24:16 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r303921 - head/sys/kern
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Author: mjg
Date: Wed Aug 10 15:24:15 2016
New Revision: 303921
URL: https://svnweb.freebsd.org/changeset/base/303921

Log:
  sigio: do a lockless check in funsetownlist
  
  There is no need to grab the lock first to see if sigio is used, and it
  typically is not.

Modified:
  head/sys/kern/kern_descrip.c

Modified: head/sys/kern/kern_descrip.c
==============================================================================
--- head/sys/kern/kern_descrip.c	Wed Aug 10 15:16:28 2016	(r303920)
+++ head/sys/kern/kern_descrip.c	Wed Aug 10 15:24:15 2016	(r303921)
@@ -942,6 +942,8 @@ funsetown(struct sigio **sigiop)
 {
 	struct sigio *sigio;
 
+	if (*sigiop == NULL)
+		return;
 	SIGIO_LOCK();
 	sigio = *sigiop;
 	if (sigio == NULL) {