libprocessgroup: Use WriteStringToFd for WriteFileAction

Using WriteStringToFile will hold kernfs_mutex which is a big lock,
so use WriteStringToFd instead. Besides, also support fd cache for it.

Bug: 206970384
Test: build pass
(cherry picked from commit e808841d72816c68da3d6d9f451aba71bf4188bc)
(cherry picked from commit b8d7ac60bdeca738346b61a1b84be34f0072af2f)
Merged-In: Id79f9e1095f52079393c58edb9a4d526f4cc6b5e
Change-Id: Id79f9e1095f52079393c58edb9a4d526f4cc6b5e

2 files changed, 109 insertions, 53 deletions

diff --git a/libprocessgroup/task_profiles.cpp b/libprocessgroup/task_profiles.cpp
index e935f99de..3834f9194 100644
--- a/libprocessgroup/task_profiles.cpp
+++ b/libprocessgroup/task_profiles.cpp
@@ -144,30 +144,13 @@ bool SetAttributeAction::ExecuteForTask(int tid) const {
     return true;
 }
 
-bool SetCgroupAction::IsAppDependentPath(const std::string& path) {
-    return path.find("<uid>", 0) != std::string::npos || path.find("<pid>", 0) != std::string::npos;
-}
-
-SetCgroupAction::SetCgroupAction(const CgroupController& c, const std::string& p)
-    : controller_(c), path_(p) {
-    // file descriptors for app-dependent paths can't be cached
-    if (IsAppDependentPath(path_)) {
-        // file descriptor is not cached
-        fd_.reset(FDS_APP_DEPENDENT);
-        return;
-    }
-
-    // file descriptor can be cached later on request
-    fd_.reset(FDS_NOT_CACHED);
-}
-
-void SetCgroupAction::EnableResourceCaching() {
+void CachedFdProfileAction::EnableResourceCaching() {
     std::lock_guard<std::mutex> lock(fd_mutex_);
     if (fd_ != FDS_NOT_CACHED) {
         return;
     }
 
-    std::string tasks_path = controller_.GetTasksFilePath(path_);
+    std::string tasks_path = GetPath();
 
     if (access(tasks_path.c_str(), W_OK) != 0) {
         // file is not accessible
@@ -185,7 +168,7 @@ void SetCgroupAction::EnableResourceCaching() {
     fd_ = std::move(fd);
 }
 
-void SetCgroupAction::DropResourceCaching() {
+void CachedFdProfileAction::DropResourceCaching() {
     std::lock_guard<std::mutex> lock(fd_mutex_);
     if (fd_ == FDS_NOT_CACHED) {
         return;
@@ -194,6 +177,26 @@ void SetCgroupAction::DropResourceCaching() {
     fd_.reset(FDS_NOT_CACHED);
 }
 
+bool CachedFdProfileAction::IsAppDependentPath(const std::string& path) {
+    return path.find("<uid>", 0) != std::string::npos || path.find("<pid>", 0) != std::string::npos;
+}
+
+void CachedFdProfileAction::InitFd(const std::string& path) {
+    // file descriptors for app-dependent paths can't be cached
+    if (IsAppDependentPath(path)) {
+        // file descriptor is not cached
+        fd_.reset(FDS_APP_DEPENDENT);
+        return;
+    }
+    // file descriptor can be cached later on request
+    fd_.reset(FDS_NOT_CACHED);
+}
+
+SetCgroupAction::SetCgroupAction(const CgroupController& c, const std::string& p)
+    : controller_(c), path_(p) {
+    InitFd(controller_.GetTasksFilePath(path_));
+}
+
 bool SetCgroupAction::AddTidToCgroup(int tid, int fd, const char* controller_name) {
     if (tid <= 0) {
         return true;
@@ -270,7 +273,7 @@ bool SetCgroupAction::ExecuteForTask(int tid) const {
     std::string tasks_path = controller()->GetTasksFilePath(path_);
     unique_fd tmp_fd(TEMP_FAILURE_RETRY(open(tasks_path.c_str(), O_WRONLY | O_CLOEXEC)));
     if (tmp_fd < 0) {
-        PLOG(WARNING) << "Failed to open " << tasks_path << ": " << strerror(errno);
+        PLOG(WARNING) << "Failed to open " << tasks_path;
         return false;
     }
     if (!AddTidToCgroup(tid, tmp_fd, controller()->name())) {
@@ -281,37 +284,73 @@ bool SetCgroupAction::ExecuteForTask(int tid) const {
     return true;
 }
 
-bool WriteFileAction::ExecuteForProcess(uid_t uid, pid_t pid) const {
-    std::string filepath(filepath_), value(value_);
+WriteFileAction::WriteFileAction(const std::string& path, const std::string& value,
+                                 bool logfailures)
+    : path_(path), value_(value), logfailures_(logfailures) {
+    InitFd(path_);
+}
 
-    filepath = StringReplace(filepath, "<uid>", std::to_string(uid), true);
-    filepath = StringReplace(filepath, "<pid>", std::to_string(pid), true);
-    value = StringReplace(value, "<uid>", std::to_string(uid), true);
-    value = StringReplace(value, "<pid>", std::to_string(pid), true);
+bool WriteFileAction::WriteValueToFile(const std::string& value, const std::string& path,
+                                       bool logfailures) {
+    // Use WriteStringToFd instead of WriteStringToFile because the latter will open file with
+    // O_TRUNC which causes kernfs_mutex contention
+    unique_fd tmp_fd(TEMP_FAILURE_RETRY(open(path.c_str(), O_WRONLY | O_CLOEXEC)));
+
+    if (tmp_fd < 0) {
+        if (logfailures) PLOG(WARNING) << "Failed to open " << path;
+        return false;
+    }
 
-    if (!WriteStringToFile(value, filepath)) {
-        if (logfailures_) PLOG(ERROR) << "Failed to write '" << value << "' to " << filepath;
+    if (!WriteStringToFd(value, tmp_fd)) {
+        if (logfailures) PLOG(ERROR) << "Failed to write '" << value << "' to " << path;
         return false;
     }
 
     return true;
 }
 
+bool WriteFileAction::ExecuteForProcess(uid_t uid, pid_t pid) const {
+    std::lock_guard<std::mutex> lock(fd_mutex_);
+    std::string value(value_);
+    std::string path(path_);
+
+    value = StringReplace(value, "<uid>", std::to_string(uid), true);
+    value = StringReplace(value, "<pid>", std::to_string(pid), true);
+    path = StringReplace(path, "<uid>", std::to_string(uid), true);
+    path = StringReplace(path, "<pid>", std::to_string(pid), true);
+
+    return WriteValueToFile(value, path, logfailures_);
+}
+
 bool WriteFileAction::ExecuteForTask(int tid) const {
-    std::string filepath(filepath_), value(value_);
+    std::lock_guard<std::mutex> lock(fd_mutex_);
+    std::string value(value_);
     int uid = getuid();
 
-    filepath = StringReplace(filepath, "<uid>", std::to_string(uid), true);
-    filepath = StringReplace(filepath, "<pid>", std::to_string(tid), true);
     value = StringReplace(value, "<uid>", std::to_string(uid), true);
     value = StringReplace(value, "<pid>", std::to_string(tid), true);
 
-    if (!WriteStringToFile(value, filepath)) {
-        if (logfailures_) PLOG(ERROR) << "Failed to write '" << value << "' to " << filepath;
+    if (IsFdValid()) {
+        // fd is cached, reuse it
+        if (!WriteStringToFd(value, fd_)) {
+            if (logfailures_) PLOG(ERROR) << "Failed to write '" << value << "' to " << path_;
+            return false;
+        }
+        return true;
+    }
+
+    if (fd_ == FDS_INACCESSIBLE) {
+        // no permissions to access the file, ignore
+        return true;
+    }
+
+    if (fd_ == FDS_APP_DEPENDENT) {
+        // application-dependent path can't be used with tid
+        PLOG(ERROR) << "Application profile can't be applied to a thread";
         return false;
     }
 
-    return true;
+    return WriteValueToFile(value, path_, logfailures_);
 }
 
 bool ApplyProfileAction::ExecuteForProcess(uid_t uid, pid_t pid) const {
diff --git a/libprocessgroup/task_profiles.h b/libprocessgroup/task_profiles.h
index 97c38f4f3..278892dd5 100644
--- a/libprocessgroup/task_profiles.h
+++ b/libprocessgroup/task_profiles.h
@@ -108,50 +108,67 @@ class SetAttributeAction : public ProfileAction {
     std::string value_;
 };
 
-// Set cgroup profile element
-class SetCgroupAction : public ProfileAction {
+// Abstract profile element for cached fd
+class CachedFdProfileAction : public ProfileAction {
   public:
-    SetCgroupAction(const CgroupController& c, const std::string& p);
-
-    virtual bool ExecuteForProcess(uid_t uid, pid_t pid) const;
-    virtual bool ExecuteForTask(int tid) const;
     virtual void EnableResourceCaching();
     virtual void DropResourceCaching();
 
-    const CgroupController* controller() const { return &controller_; }
-    std::string path() const { return path_; }
-
-  private:
+  protected:
     enum FdState {
         FDS_INACCESSIBLE = -1,
         FDS_APP_DEPENDENT = -2,
         FDS_NOT_CACHED = -3,
     };
 
-    CgroupController controller_;
-    std::string path_;
     android::base::unique_fd fd_;
     mutable std::mutex fd_mutex_;
 
     static bool IsAppDependentPath(const std::string& path);
-    static bool AddTidToCgroup(int tid, int fd, const char* controller_name);
 
+    void InitFd(const std::string& path);
     bool IsFdValid() const { return fd_ > FDS_INACCESSIBLE; }
+
+    virtual const std::string GetPath() const = 0;
+};
+
+// Set cgroup profile element
+class SetCgroupAction : public CachedFdProfileAction {
+  public:
+    SetCgroupAction(const CgroupController& c, const std::string& p);
+
+    virtual bool ExecuteForProcess(uid_t uid, pid_t pid) const;
+    virtual bool ExecuteForTask(int tid) const;
+
+    const CgroupController* controller() const { return &controller_; }
+
+  protected:
+    const std::string GetPath() const override { return controller_.GetTasksFilePath(path_); }
+
+  private:
+    CgroupController controller_;
+    std::string path_;
+
+    static bool AddTidToCgroup(int tid, int fd, const char* controller_name);
 };
 
 // Write to file action
-class WriteFileAction : public ProfileAction {
+class WriteFileAction : public CachedFdProfileAction {
   public:
-    WriteFileAction(const std::string& filepath, const std::string& value,
-                    bool logfailures) noexcept
-        : filepath_(filepath), value_(value), logfailures_(logfailures) {}
+    WriteFileAction(const std::string& path, const std::string& value, bool logfailures);
 
     virtual bool ExecuteForProcess(uid_t uid, pid_t pid) const;
     virtual bool ExecuteForTask(int tid) const;
 
+  protected:
+    const std::string GetPath() const override { return path_; }
+
   private:
-    std::string filepath_, value_;
+    std::string path_, value_;
     bool logfailures_;
+
+    static bool WriteValueToFile(const std::string& value, const std::string& path,
+                                 bool logfailures);
 };
 
 class TaskProfile {