heapprofd_client: fork mode: avoid atfork handlers and SIGCHILD by using clone(2).
This should be less invasive for the host process. Especially considering that
during runtime init, the fork was happening at an "arbitrary" point in time
from the perspective of the process' threads.
Tested only manually so far.
Change-Id: I3cc857b5bc4922a4497d6ee7fa4f6305c6eb6e44
diff --git a/src/profiling/memory/malloc_hooks.cc b/src/profiling/memory/malloc_hooks.cc
index 4178610..fb95146 100644
--- a/src/profiling/memory/malloc_hooks.cc
+++ b/src/profiling/memory/malloc_hooks.cc
@@ -145,18 +145,42 @@
return g_dispatch.load(std::memory_order_relaxed);
}
-// Note: android_mallopt(M_RESET_HOOKS) is mutually exclusive with initialize
-// (concurrent calls get discarded).
-void ShutdownLazy() {
- ScopedSpinlock s(&g_client_lock, ScopedSpinlock::Mode::Blocking);
- if (!g_client.ref()) // other invocation already initiated shutdown
- return;
+int CloneWithoutSigchld() {
+ return clone(nullptr, nullptr, 0, nullptr);
+}
- // Clear primary shared pointer, such that later hook invocations become nops.
- g_client.ref().reset();
+int ForklikeClone() {
+ return clone(nullptr, nullptr, SIGCHLD, nullptr);
+}
- if (!android_mallopt(M_RESET_HOOKS, nullptr, 0))
- PERFETTO_PLOG("Unpatching heapprofd hooks failed.");
+// Like daemon(), but using clone to avoid invoking pthread_atfork(3) handlers.
+int Daemonize() {
+ switch (ForklikeClone()) {
+ case -1:
+ PERFETTO_PLOG("Daemonize.clone");
+ return -1;
+ break;
+ case 0:
+ break;
+ default:
+ _exit(0);
+ break;
+ }
+ if (setsid() == -1) {
+ PERFETTO_PLOG("Daemonize.setsid");
+ return -1;
+ }
+ // best effort chdir & fd close
+ chdir("/");
+ int fd = open("/dev/null", O_RDWR, 0);
+ if (fd != -1) {
+ dup2(fd, STDIN_FILENO);
+ dup2(fd, STDOUT_FILENO);
+ dup2(fd, STDERR_FILENO);
+ if (fd > STDERR_FILENO)
+ close(fd);
+ }
+ return 0;
}
std::string ReadSystemProperty(const char* key) {
@@ -231,16 +255,19 @@
return nullptr;
}
- pid_t fork_pid = fork();
- if (fork_pid == -1) {
- PERFETTO_PLOG("Failed to fork.");
+ // Use fork-like clone to avoid invoking the host's pthread_atfork(3)
+ // handlers. Also avoid sending the current process a SIGCHILD to further
+ // reduce our interference.
+ pid_t clone_pid = CloneWithoutSigchld();
+ if (clone_pid == -1) {
+ PERFETTO_PLOG("Failed to clone.");
return nullptr;
}
- if (fork_pid == 0) { // child
- // daemon() forks again, terminating the calling thread (i.e. the direct
+ if (clone_pid == 0) { // child
+ // Daemonize clones again, terminating the calling thread (i.e. the direct
// child of the original process). So the rest of this codepath will be
- // executed in a (new) reparented process.
- if (daemon(/*nochdir=*/0, /*noclose=*/0) == -1) {
+ // executed in a new reparented process.
+ if (Daemonize() == -1) {
PERFETTO_PLOG("Daemonization failed.");
_exit(1);
}
@@ -271,10 +298,10 @@
// Wait on the immediate child to exit (allow for ECHILD in the unlikely case
// we're in a process that has made its children unwaitable).
- siginfo_t unused = {};
- if (PERFETTO_EINTR(waitid(P_PID, fork_pid, &unused, WEXITED)) == -1 &&
+ int unused = 0;
+ if (PERFETTO_EINTR(waitpid(clone_pid, &unused, __WCLONE)) == -1 &&
errno != ECHILD) {
- PERFETTO_PLOG("Failed to waitid on immediate child.");
+ PERFETTO_PLOG("Failed to waitpid on immediate child.");
return nullptr;
}
@@ -282,6 +309,20 @@
unhooked_allocator);
}
+// Note: android_mallopt(M_RESET_HOOKS) is mutually exclusive with initialize
+// (concurrent calls get discarded).
+void ShutdownLazy() {
+ ScopedSpinlock s(&g_client_lock, ScopedSpinlock::Mode::Blocking);
+ if (!g_client.ref()) // other invocation already initiated shutdown
+ return;
+
+ // Clear primary shared pointer, such that later hook invocations become nops.
+ g_client.ref().reset();
+
+ if (!android_mallopt(M_RESET_HOOKS, nullptr, 0))
+ PERFETTO_PLOG("Unpatching heapprofd hooks failed.");
+}
+
} // namespace
// Setup for the rest of profiling. The first time profiling is triggered in a
@@ -318,10 +359,10 @@
: CreateClientForCentralDaemon(unhooked_allocator);
if (!client) {
- PERFETTO_LOG("Client not initialized, not installing hooks.");
+ PERFETTO_LOG("heapprofd_client not initialized, not installing hooks.");
return false;
}
- PERFETTO_DLOG("Client initialized.");
+ PERFETTO_LOG("heapprofd_client initialized.");
g_client.ref() = std::move(client);
return true;