Kill the child process when the parent process dies.

When we have a process hierarchy, such as artd->odrefresh->dex2oat, we
want to be able to kill a subtree. For example, if we kill odrefresh, we
want dex2oat to be killed as well; if we kill artd, we want both
odrefresh and dex2oat to be killed as well. This can be achieved by
PR_SET_PDEATHSIG.

Bug: 311377497
Test: Kill odrefresh and see dex2oat killed.
Change-Id: I28cc271f5c37b9ad50bee179eb9b211cb3545a2f

1 files changed, 12 insertions, 0 deletions

diff --git a/runtime/exec_utils.cc b/runtime/exec_utils.cc
index 1266ed18f7..1914d506cd 100644
--- a/runtime/exec_utils.cc
+++ b/runtime/exec_utils.cc
@@ -17,6 +17,8 @@
 #include "exec_utils.h"
 
 #include <poll.h>
+#include <signal.h>
+#include <sys/prctl.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
@@ -65,6 +67,10 @@ std::string ToCommandLine(const std::vector<std::string>& args) {
 // If there is a runtime (Runtime::Current != nullptr) then the subprocess is created with the
 // same environment that existed when the runtime was started.
 // Returns the process id of the child process on success, -1 otherwise.
+// The child is killed as soon as the caller thread dies, the caller thread needs to stay around and
+// wait for the child. Therefore, this function is most suitable to be used by
+// `ExecAndReturnResult`, which does the wait. It's not suitable to be used for fire-and-forget
+// exec's.
 pid_t ExecWithoutWait(const std::vector<std::string>& arg_vector, std::string* error_msg) {
   // Convert the args to char pointers.
   const char* program = arg_vector[0].c_str();
@@ -83,6 +89,12 @@ pid_t ExecWithoutWait(const std::vector<std::string>& arg_vector, std::string* e
     // change process groups, so we don't get reaped by ProcessManager
     setpgid(0, 0);
 
+    // Kill the child process when the parent process dies.
+    if (prctl(PR_SET_PDEATHSIG, SIGKILL) != 0) {
+      // This should never happen.
+      PLOG(FATAL) << "Failed to call prctl";
+    }
+
     // (b/30160149): protect subprocesses from modifications to LD_LIBRARY_PATH, etc.
     // Use the snapshot of the environment from the time the runtime was created.
     char** envp = (Runtime::Current() == nullptr) ? nullptr : Runtime::Current()->GetEnvSnapshot();