Reduce log spam from libprocessgroup

EBUSY is expected when removing process group path if process is still
active. ESRCH is expected when kill if process died already. ENOENT is
also expected when opening cgroup path if process died already.
This CL also skip removing parent path if child failed when remove
process group.

Bug: 125340804
Test: Build and boot
Change-Id: Ief3b9cb913035a4050f6cf79c8b1e2f098e18244
diff --git a/libprocessgroup/processgroup.cpp b/libprocessgroup/processgroup.cpp
index e9dec12..c6710d0 100644
--- a/libprocessgroup/processgroup.cpp
+++ b/libprocessgroup/processgroup.cpp
@@ -170,8 +170,9 @@
     return ret;
 }
 
-static void RemoveUidProcessGroups(const std::string& uid_path) {
+static bool RemoveUidProcessGroups(const std::string& uid_path) {
     std::unique_ptr<DIR, decltype(&closedir)> uid(opendir(uid_path.c_str()), closedir);
+    bool empty = true;
     if (uid != NULL) {
         dirent* dir;
         while ((dir = readdir(uid.get())) != nullptr) {
@@ -185,9 +186,15 @@
 
             auto path = StringPrintf("%s/%s", uid_path.c_str(), dir->d_name);
             LOG(VERBOSE) << "Removing " << path;
-            if (rmdir(path.c_str()) == -1) PLOG(WARNING) << "Failed to remove " << path;
+            if (rmdir(path.c_str()) == -1) {
+                if (errno != EBUSY) {
+                    PLOG(WARNING) << "Failed to remove " << path;
+                }
+                empty = false;
+            }
         }
     }
+    return empty;
 }
 
 void removeAllProcessGroups() {
@@ -219,9 +226,14 @@
                 }
 
                 auto path = StringPrintf("%s/%s", cgroup_root_path.c_str(), dir->d_name);
-                RemoveUidProcessGroups(path);
+                if (!RemoveUidProcessGroups(path)) {
+                    LOG(VERBOSE) << "Skip removing " << path;
+                    continue;
+                }
                 LOG(VERBOSE) << "Removing " << path;
-                if (rmdir(path.c_str()) == -1) PLOG(WARNING) << "Failed to remove " << path;
+                if (rmdir(path.c_str()) == -1 && errno != EBUSY) {
+                    PLOG(WARNING) << "Failed to remove " << path;
+                }
             }
         }
     }
@@ -249,6 +261,10 @@
     auto path = ConvertUidPidToPath(cgroup, uid, initialPid) + PROCESSGROUP_CGROUP_PROCS_FILE;
     std::unique_ptr<FILE, decltype(&fclose)> fd(fopen(path.c_str(), "re"), fclose);
     if (!fd) {
+        if (errno == ENOENT) {
+            // This happens when process is already dead
+            return 0;
+        }
         PLOG(WARNING) << "Failed to open process cgroup uid " << uid << " pid " << initialPid;
         return -1;
     }
@@ -293,7 +309,7 @@
         LOG(VERBOSE) << "Killing process group " << -pgid << " in uid " << uid
                      << " as part of process cgroup " << initialPid;
 
-        if (kill(-pgid, signal) == -1) {
+        if (kill(-pgid, signal) == -1 && errno != ESRCH) {
             PLOG(WARNING) << "kill(" << -pgid << ", " << signal << ") failed";
         }
     }
@@ -303,7 +319,7 @@
         LOG(VERBOSE) << "Killing pid " << pid << " in uid " << uid << " as part of process cgroup "
                      << initialPid;
 
-        if (kill(pid, signal) == -1) {
+        if (kill(pid, signal) == -1 && errno != ESRCH) {
             PLOG(WARNING) << "kill(" << pid << ", " << signal << ") failed";
         }
     }