fix raise semantics with threads.

src/signal/raise.c

@@ -1,7 +1,18 @@
 #include <signal.h>
+#include <errno.h>
 #include "syscall.h"
 
 int raise(int sig)
 {
-	return __syscall_kill(__syscall_getpid(), sig);
+	int pid, tid, ret;
+	/* Getting the pid/tid pair is not atomic, and could give wrong
+	 * result if a fork occurs in a signal handler between the two
+	 * syscalls. Use the tgkill syscall's ESRCH semantics to detect
+	 * this condition and retry. */
+	do {
+		tid = syscall0(__NR_gettid);
+		pid = syscall0(__NR_getpid);
+		ret = syscall3(__NR_tgkill, pid, tid, sig);
+	} while (ret<0 && errno == ESRCH);
+	return ret;
 }