Make sem_post() safe to call from within a signal handler, as required by

POSIX/SUSv2.

lib/libc/gen/sem_post.3

@@ -48,6 +48,9 @@ If there are threads blocked on the semaphore when
 is called, then the highest priority thread that has been blocked the longest on
 the semaphore will be allowed to return from
 .Fn sem_wait .
+.Pp
+.Fn sem_post
+is signal-reentrant and may be called within signal handlers.
 .Sh RETURN VALUES
 If successful,
 .Fn sem_post

lib/libc_r/man/sem_post.3

@@ -48,6 +48,9 @@ If there are threads blocked on the semaphore when
 is called, then the highest priority thread that has been blocked the longest on
 the semaphore will be allowed to return from
 .Fn sem_wait .
+.Pp
+.Fn sem_post
+is signal-reentrant and may be called within signal handlers.
 .Sh RETURN VALUES
 If successful,
 .Fn sem_post

lib/libc_r/uthread/uthread_sem.c

@@ -206,6 +206,12 @@ sem_post(sem_t *sem)
 
 	_SEM_CHECK_VALIDITY(sem);
 
+	/*
+	 * sem_post() is required to be safe to call from within signal
+	 * handlers.  Thus, we must defer signals.
+	 */
+	_thread_kern_sig_defer();
+
 	pthread_mutex_lock(&(*sem)->lock);
 
 	(*sem)->count++;
@@ -221,6 +227,7 @@ sem_post(sem_t *sem)
 
 	pthread_mutex_unlock(&(*sem)->lock);
 
+	_thread_kern_sig_defer();
 	retval = 0;
   RETURN:
 	return retval;

lib/libkse/thread/thr_sem.c

@@ -206,6 +206,12 @@ sem_post(sem_t *sem)
 
 	_SEM_CHECK_VALIDITY(sem);
 
+	/*
+	 * sem_post() is required to be safe to call from within signal
+	 * handlers.  Thus, we must defer signals.
+	 */
+	_thread_kern_sig_defer();
+
 	pthread_mutex_lock(&(*sem)->lock);
 
 	(*sem)->count++;
@@ -221,6 +227,7 @@ sem_post(sem_t *sem)
 
 	pthread_mutex_unlock(&(*sem)->lock);
 
+	_thread_kern_sig_defer();
 	retval = 0;
   RETURN:
 	return retval;

lib/libpthread/man/sem_post.3

@@ -48,6 +48,9 @@ If there are threads blocked on the semaphore when
 is called, then the highest priority thread that has been blocked the longest on
 the semaphore will be allowed to return from
 .Fn sem_wait .
+.Pp
+.Fn sem_post
+is signal-reentrant and may be called within signal handlers.
 .Sh RETURN VALUES
 If successful,
 .Fn sem_post

lib/libpthread/thread/thr_sem.c

@@ -206,6 +206,12 @@ sem_post(sem_t *sem)
 
 	_SEM_CHECK_VALIDITY(sem);
 
+	/*
+	 * sem_post() is required to be safe to call from within signal
+	 * handlers.  Thus, we must defer signals.
+	 */
+	_thread_kern_sig_defer();
+
 	pthread_mutex_lock(&(*sem)->lock);
 
 	(*sem)->count++;
@@ -221,6 +227,7 @@ sem_post(sem_t *sem)
 
 	pthread_mutex_unlock(&(*sem)->lock);
 
+	_thread_kern_sig_defer();
 	retval = 0;
   RETURN:
 	return retval;