Fix race conditions in pldd that may leave the process stopped after …

…detaching

Fixes bug 15804

ChangeLog

@@ -1,3 +1,9 @@
+2014-02-24  Andreas Schwab  <schwab@suse.de>
+
+	[BZ #15804]
+	* elf/pldd.c (wait_for_ptrace_stop): New function.
+	(main): Call it after attaching.
+
 2014-02-22  Roland McGrath  <roland@hack.frob.com>
 
 	* Makerules ($(common-objpfx)Versions.v.i): No longer depend

NEWS

@@ -9,7 +9,7 @@ Version 2.20
 
 * The following bugs are resolved with this release:
 
-  15894, 16447, 16545, 16574, 16600, 16609, 16610, 16611.
+  15804, 15894, 16447, 16545, 16574, 16600, 16609, 16610, 16611.
 
 * The am33 port, which had not worked for several years, has been removed
   from ports.

elf/pldd.c

@@ -34,6 +34,7 @@
 #include <unistd.h>
 #include <sys/ptrace.h>
 #include <sys/stat.h>
+#include <sys/wait.h>
 
 #include <ldsodefs.h>
 #include <version.h>
@@ -82,6 +83,7 @@ static char *exe;
 
 /* Local functions.  */
 static int get_process_info (int dfd, long int pid);
+static void wait_for_ptrace_stop (long int pid);
 
 
 int
@@ -170,6 +172,8 @@ main (int argc, char *argv[])
 		 tid);
 	}
 
+      wait_for_ptrace_stop (tid);
+
       struct thread_list *newp = alloca (sizeof (*newp));
       newp->tid = tid;
       newp->next = thread_list;
@@ -194,6 +198,27 @@ main (int argc, char *argv[])
 }
 
 
+/* Wait for PID to enter ptrace-stop state after being attached.  */
+static void
+wait_for_ptrace_stop (long int pid)
+{
+  int status;
+
+  /* While waiting for SIGSTOP being delivered to the tracee we have to
+     reinject any other pending signal.  Ignore all other errors.  */
+  while (waitpid (pid, &status, __WALL) == pid && WIFSTOPPED (status))
+    {
+      /* The STOP signal should not be delivered to the tracee.  */
+      if (WSTOPSIG (status) == SIGSTOP)
+	return;
+      if (ptrace (PTRACE_CONT, pid, NULL,
+		  (void *) (uintptr_t) WSTOPSIG (status)))
+	/* The only possible error is that the process died.  */
+	return;
+    }
+}
+
+
 /* Handle program arguments.  */
 static error_t
 parse_opt (int key, char *arg, struct argp_state *state)