svn commit: r273605 - head/lib/libc/net

[Mark Johnston]

Author: markj
Date: Fri Oct 24 20:29:14 2014
New Revision: 273605
URL: https://svnweb.freebsd.org/changeset/base/273605

Log:
  Eliminate conf_lock and instead rely on the NSS write lock to protect
  NSS configuration state.
  
  As a side effect, this fixes a race condition which can occur if multiple
  threads call nsdispatch(3) concurrently before nsswitch.conf has been
  parsed. Previously, the thread holding conf_lock could cause other threads
  to return from nss_configure() before nsswitch.conf had been parsed, forcing
  them to fall back to the default sources for their NSS methods.
  
  Reviewed by:		jhb
  Differential Revision:	https://reviews.freebsd.org/D994
  MFC after:		1 month
  Sponsored by:		EMC / Isilon Storage Division

Modified:
  head/lib/libc/net/nsdispatch.c

Modified: head/lib/libc/net/nsdispatch.c
==============================================================================
--- head/lib/libc/net/nsdispatch.c	Fri Oct 24 20:02:44 2014	(r273604)
+++ head/lib/libc/net/nsdispatch.c	Fri Oct 24 20:29:14 2014	(r273605)
@@ -329,7 +329,6 @@ _nsdbtdump(const ns_dbt *dbt)
 static int
 nss_configure(void)
 {
-	static pthread_mutex_t conf_lock = PTHREAD_MUTEX_INITIALIZER;
 	static time_t	 confmod;
 	struct stat	 statbuf;
 	int		 result, isthreaded;
@@ -353,13 +352,14 @@ nss_configure(void)
 	if (statbuf.st_mtime <= confmod)
 		return (0);
 	if (isthreaded) {
-	    result = _pthread_mutex_trylock(&conf_lock);
-	    if (result != 0)
-		    return (0);
 	    (void)_pthread_rwlock_unlock(&nss_lock);
 	    result = _pthread_rwlock_wrlock(&nss_lock);
 	    if (result != 0)
-		    goto fin2;
+		    return (result);
+	    if (stat(path, &statbuf) != 0)
+		    goto fin;
+	    if (statbuf.st_mtime <= confmod)
+		    goto fin;
 	}
 	_nsyyin = fopen(path, "re");
 	if (_nsyyin == NULL)
@@ -390,9 +390,6 @@ fin:
 	    if (result == 0)
 		    result = _pthread_rwlock_rdlock(&nss_lock);
 	}
-fin2:
-	if (isthreaded)
-		(void)_pthread_mutex_unlock(&conf_lock);
 	return (result);
 }