Fix IsUsable to check for each controller separately

CgroupController::IsUsable is using a global static variable to store the
existence of the controller. That means the first controller existence
check would affect all other controllers. Fix this by making this variable
to be a member of CgroupController class so that each controller can check
for its existence independently of other controllers.

Fixes: aa1d54f0ccbb ("Remove ACgroupController_getFlags to fix API breakage")
Bug: 136020193
Test: adb shell cat /proc/$pid/task/*/cgroup" prints "cpuset:/top-app"
Test: for new launched activity process
Change-Id: I4741a9126ea494122d5b2b1a0c4d7252bff6025c
Signed-off-by: Suren Baghdasaryan <surenb@google.com>

2 files changed, 16 insertions, 5 deletions

diff --git a/libprocessgroup/cgroup_map.cpp b/libprocessgroup/cgroup_map.cpp
index 9797d763f..20ae2be77 100644
--- a/libprocessgroup/cgroup_map.cpp
+++ b/libprocessgroup/cgroup_map.cpp
@@ -67,11 +67,14 @@ bool CgroupController::HasValue() const {
     return controller_ != nullptr;
 }
 
-bool CgroupController::IsUsable() const {
+bool CgroupController::IsUsable() {
     if (!HasValue()) return false;
 
-    static bool enabled = (access(GetProcsFilePath("", 0, 0).c_str(), F_OK) == 0);
-    return enabled;
+    if (state_ == UNKNOWN) {
+        state_ = access(GetProcsFilePath("", 0, 0).c_str(), F_OK) == 0 ? USABLE : MISSING;
+    }
+
+    return state_ == USABLE;
 }
 
 std::string CgroupController::GetTasksFilePath(const std::string& rel_path) const {
diff --git a/libprocessgroup/cgroup_map.h b/libprocessgroup/cgroup_map.h
index 935041242..427d71b40 100644
--- a/libprocessgroup/cgroup_map.h
+++ b/libprocessgroup/cgroup_map.h
@@ -31,20 +31,28 @@
 class CgroupController {
   public:
     // Does not own controller
-    explicit CgroupController(const ACgroupController* controller) : controller_(controller) {}
+    explicit CgroupController(const ACgroupController* controller)
+        : controller_(controller), state_(UNKNOWN) {}
 
     uint32_t version() const;
     const char* name() const;
     const char* path() const;
 
     bool HasValue() const;
-    bool IsUsable() const;
+    bool IsUsable();
 
     std::string GetTasksFilePath(const std::string& path) const;
     std::string GetProcsFilePath(const std::string& path, uid_t uid, pid_t pid) const;
     bool GetTaskGroup(int tid, std::string* group) const;
   private:
+    enum ControllerState {
+        UNKNOWN = 0,
+        USABLE = 1,
+        MISSING = 2,
+    };
+
     const ACgroupController* controller_ = nullptr;
+    ControllerState state_;
 };
 
 class CgroupMap {