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Eliminate conf_lock and instead rely on the NSS write lock to protect

Browse Source 
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
This commit is contained in:
Mark Johnston 2014-10-24 20:29:14 +00:00
parent 53e1ffbbce
commit f53b045631
1 changed files with 5 additions and 8 deletions

13
lib/libc/net/nsdispatch.c

@ -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);
}