libprocessgroup/processgroup.cpp - android-core - Git at Google

 /*
  *  Copyright 2014 Google, Inc
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
  *  You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  *  Unless required by applicable law or agreed to in writing, software
  *  distributed under the License is distributed on an "AS IS" BASIS,
  *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */

 //#define LOG_NDEBUG 0
 #define LOG_TAG "libprocessgroup"

 #include <assert.h>
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>

 #include <chrono>
 #include <map>
 #include <memory>
 #include <mutex>
 #include <set>
 #include <string>
 #include <thread>

 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
 #include <cutils/android_filesystem_config.h>
 #include <processgroup/processgroup.h>
 #include <task_profiles.h>

 using android::base::GetBoolProperty;
 using android::base::StartsWith;
 using android::base::StringPrintf;
 using android::base::WriteStringToFile;

 using namespace std::chrono_literals;

 #define PROCESSGROUP_CGROUP_PROCS_FILE "/cgroup.procs"

 bool CgroupGetControllerPath(const std::string& cgroup_name, std::string* path) {
     auto controller = CgroupMap::GetInstance().FindController(cgroup_name);

     if (!controller.HasValue()) {
         return false;
     }

     if (path) {
         *path = controller.path();
     }

     return true;
 }

 bool CgroupGetAttributePath(const std::string& attr_name, std::string* path) {
     const TaskProfiles& tp = TaskProfiles::GetInstance();
     const ProfileAttribute* attr = tp.GetAttribute(attr_name);

     if (attr == nullptr) {
         return false;
     }

     if (path) {
         *path = StringPrintf("%s/%s", attr->controller()->path(), attr->file_name().c_str());
     }

     return true;
 }

 bool CgroupGetAttributePathForTask(const std::string& attr_name, int tid, std::string* path) {
     const TaskProfiles& tp = TaskProfiles::GetInstance();
     const ProfileAttribute* attr = tp.GetAttribute(attr_name);

     if (attr == nullptr) {
         return false;
     }

     if (!attr->GetPathForTask(tid, path)) {
         PLOG(ERROR) << "Failed to find cgroup for tid " << tid;
         return false;
     }

     return true;
 }

 bool UsePerAppMemcg() {
     bool low_ram_device = GetBoolProperty("ro.config.low_ram", false);
     return GetBoolProperty("ro.config.per_app_memcg", low_ram_device);
 }

 static bool isMemoryCgroupSupported() {
     std::string cgroup_name;
     static bool memcg_supported = CgroupMap::GetInstance().FindController("memory").HasValue();

     return memcg_supported;
 }

 bool SetProcessProfiles(uid_t uid, pid_t pid, const std::vector<std::string>& profiles,
                         bool use_fd_cache) {
     const TaskProfiles& tp = TaskProfiles::GetInstance();

     for (const auto& name : profiles) {
         TaskProfile* profile = tp.GetProfile(name);
         if (profile != nullptr) {
             if (use_fd_cache) {
                 profile->EnableResourceCaching();
             }
             if (!profile->ExecuteForProcess(uid, pid)) {
                 PLOG(WARNING) << "Failed to apply " << name << " process profile";
             }
         } else {
             PLOG(WARNING) << "Failed to find " << name << "process profile";
         }
     }

     return true;
 }

 bool SetTaskProfiles(int tid, const std::vector<std::string>& profiles, bool use_fd_cache) {
     const TaskProfiles& tp = TaskProfiles::GetInstance();

     for (const auto& name : profiles) {
         TaskProfile* profile = tp.GetProfile(name);
         if (profile != nullptr) {
             if (use_fd_cache) {
                 profile->EnableResourceCaching();
             }
             if (!profile->ExecuteForTask(tid)) {
                 PLOG(WARNING) << "Failed to apply " << name << " task profile";
             }
         } else {
             PLOG(WARNING) << "Failed to find " << name << "task profile";
         }
     }

     return true;
 }

 static std::string ConvertUidToPath(const char* cgroup, uid_t uid) {
     return StringPrintf("%s/uid_%d", cgroup, uid);
 }

 static std::string ConvertUidPidToPath(const char* cgroup, uid_t uid, int pid) {
     return StringPrintf("%s/uid_%d/pid_%d", cgroup, uid, pid);
 }

 static int RemoveProcessGroup(const char* cgroup, uid_t uid, int pid) {
     int ret;

     auto uid_pid_path = ConvertUidPidToPath(cgroup, uid, pid);
     ret = rmdir(uid_pid_path.c_str());

     auto uid_path = ConvertUidToPath(cgroup, uid);
     rmdir(uid_path.c_str());

     return ret;
 }

 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) {
             if (dir->d_type != DT_DIR) {
                 continue;
             }

             if (!StartsWith(dir->d_name, "pid_")) {
                 continue;
             }

             auto path = StringPrintf("%s/%s", uid_path.c_str(), dir->d_name);
             LOG(VERBOSE) << "Removing " << path;
             if (rmdir(path.c_str()) == -1) {
                 if (errno != EBUSY) {
                     PLOG(WARNING) << "Failed to remove " << path;
                 }
                 empty = false;
             }
         }
     }
     return empty;
 }

 void removeAllProcessGroups() {
     LOG(VERBOSE) << "removeAllProcessGroups()";

     std::vector<std::string> cgroups;
     std::string path;

     if (CgroupGetControllerPath("cpuacct", &path)) {
         cgroups.push_back(path);
     }
     if (CgroupGetControllerPath("memory", &path)) {
         cgroups.push_back(path + "/apps");
     }

     for (std::string cgroup_root_path : cgroups) {
         std::unique_ptr<DIR, decltype(&closedir)> root(opendir(cgroup_root_path.c_str()), closedir);
         if (root == NULL) {
             PLOG(ERROR) << "Failed to open " << cgroup_root_path;
         } else {
             dirent* dir;
             while ((dir = readdir(root.get())) != nullptr) {
                 if (dir->d_type != DT_DIR) {
                     continue;
                 }

                 if (!StartsWith(dir->d_name, "uid_")) {
                     continue;
                 }

                 auto path = StringPrintf("%s/%s", cgroup_root_path.c_str(), dir->d_name);
                 if (!RemoveUidProcessGroups(path)) {
                     LOG(VERBOSE) << "Skip removing " << path;
                     continue;
                 }
                 LOG(VERBOSE) << "Removing " << path;
                 if (rmdir(path.c_str()) == -1 && errno != EBUSY) {
                     PLOG(WARNING) << "Failed to remove " << path;
                 }
             }
         }
     }
 }

 static bool MkdirAndChown(const std::string& path, mode_t mode, uid_t uid, gid_t gid) {
     if (mkdir(path.c_str(), mode) == -1 && errno != EEXIST) {
         return false;
     }

     if (chown(path.c_str(), uid, gid) == -1) {
         int saved_errno = errno;
         rmdir(path.c_str());
         errno = saved_errno;
         return false;
     }

     return true;
 }

 // Returns number of processes killed on success
 // Returns 0 if there are no processes in the process cgroup left to kill
 // Returns -1 on error
 static int DoKillProcessGroupOnce(const char* cgroup, uid_t uid, int initialPid, int signal) {
     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;
     }

     // We separate all of the pids in the cgroup into those pids that are also the leaders of
     // process groups (stored in the pgids set) and those that are not (stored in the pids set).
     std::set<pid_t> pgids;
     pgids.emplace(initialPid);
     std::set<pid_t> pids;

     pid_t pid;
     int processes = 0;
     while (fscanf(fd.get(), "%d\n", &pid) == 1 && pid >= 0) {
         processes++;
         if (pid == 0) {
             // Should never happen...  but if it does, trying to kill this
             // will boomerang right back and kill us!  Let's not let that happen.
             LOG(WARNING) << "Yikes, we've been told to kill pid 0!  How about we don't do that?";
             continue;
         }
         pid_t pgid = getpgid(pid);
         if (pgid == -1) PLOG(ERROR) << "getpgid(" << pid << ") failed";
         if (pgid == pid) {
             pgids.emplace(pid);
         } else {
             pids.emplace(pid);
         }
     }

     // Erase all pids that will be killed when we kill the process groups.
     for (auto it = pids.begin(); it != pids.end();) {
         pid_t pgid = getpgid(*it);
         if (pgids.count(pgid) == 1) {
             it = pids.erase(it);
         } else {
             ++it;
         }
     }

     // Kill all process groups.
     for (const auto pgid : pgids) {
         LOG(VERBOSE) << "Killing process group " << -pgid << " in uid " << uid
                      << " as part of process cgroup " << initialPid;

         if (kill(-pgid, signal) == -1 && errno != ESRCH) {
             PLOG(WARNING) << "kill(" << -pgid << ", " << signal << ") failed";
         }
     }

     // Kill remaining pids.
     for (const auto pid : pids) {
         LOG(VERBOSE) << "Killing pid " << pid << " in uid " << uid << " as part of process cgroup "
                      << initialPid;

         if (kill(pid, signal) == -1 && errno != ESRCH) {
             PLOG(WARNING) << "kill(" << pid << ", " << signal << ") failed";
         }
     }

     return feof(fd.get()) ? processes : -1;
 }

 static int KillProcessGroup(uid_t uid, int initialPid, int signal, int retries) {
     std::string cpuacct_path;
     std::string memory_path;

     CgroupGetControllerPath("cpuacct", &cpuacct_path);
     CgroupGetControllerPath("memory", &memory_path);
     memory_path += "/apps";

     const char* cgroup =
             (!access(ConvertUidPidToPath(cpuacct_path.c_str(), uid, initialPid).c_str(), F_OK))
                     ? cpuacct_path.c_str()
                     : memory_path.c_str();

     std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();

     int retry = retries;
     int processes;
     while ((processes = DoKillProcessGroupOnce(cgroup, uid, initialPid, signal)) > 0) {
         LOG(VERBOSE) << "Killed " << processes << " processes for processgroup " << initialPid;
         if (retry > 0) {
             std::this_thread::sleep_for(5ms);
             --retry;
         } else {
             break;
         }
     }

     if (processes < 0) {
         PLOG(ERROR) << "Error encountered killing process cgroup uid " << uid << " pid "
                     << initialPid;
         return -1;
     }

     std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
     auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count();

     // We only calculate the number of 'processes' when killing the processes.
     // In the retries == 0 case, we only kill the processes once and therefore
     // will not have waited then recalculated how many processes are remaining
     // after the first signals have been sent.
     // Logging anything regarding the number of 'processes' here does not make sense.

     if (processes == 0) {
         if (retries > 0) {
             LOG(INFO) << "Successfully killed process cgroup uid " << uid << " pid " << initialPid
                       << " in " << static_cast<int>(ms) << "ms";
         }
         return RemoveProcessGroup(cgroup, uid, initialPid);
     } else {
         if (retries > 0) {
             LOG(ERROR) << "Failed to kill process cgroup uid " << uid << " pid " << initialPid
                        << " in " << static_cast<int>(ms) << "ms, " << processes
                        << " processes remain";
         }
         return -1;
     }
 }

 int killProcessGroup(uid_t uid, int initialPid, int signal) {
     return KillProcessGroup(uid, initialPid, signal, 40 /*retries*/);
 }

 int killProcessGroupOnce(uid_t uid, int initialPid, int signal) {
     return KillProcessGroup(uid, initialPid, signal, 0 /*retries*/);
 }

 int createProcessGroup(uid_t uid, int initialPid, bool memControl) {
     std::string cgroup;
     if (isMemoryCgroupSupported() && (memControl || UsePerAppMemcg())) {
         CgroupGetControllerPath("memory", &cgroup);
         cgroup += "/apps";
     } else {
         CgroupGetControllerPath("cpuacct", &cgroup);
     }

     auto uid_path = ConvertUidToPath(cgroup.c_str(), uid);

     if (!MkdirAndChown(uid_path, 0750, AID_SYSTEM, AID_SYSTEM)) {
         PLOG(ERROR) << "Failed to make and chown " << uid_path;
         return -errno;
     }

     auto uid_pid_path = ConvertUidPidToPath(cgroup.c_str(), uid, initialPid);

     if (!MkdirAndChown(uid_pid_path, 0750, AID_SYSTEM, AID_SYSTEM)) {
         PLOG(ERROR) << "Failed to make and chown " << uid_pid_path;
         return -errno;
     }

     auto uid_pid_procs_file = uid_pid_path + PROCESSGROUP_CGROUP_PROCS_FILE;

     int ret = 0;
     if (!WriteStringToFile(std::to_string(initialPid), uid_pid_procs_file)) {
         ret = -errno;
         PLOG(ERROR) << "Failed to write '" << initialPid << "' to " << uid_pid_procs_file;
     }

     return ret;
 }

 static bool SetProcessGroupValue(int tid, const std::string& attr_name, int64_t value) {
     if (!isMemoryCgroupSupported()) {
         PLOG(ERROR) << "Memcg is not mounted.";
         return false;
     }

     std::string path;
     if (!CgroupGetAttributePathForTask(attr_name, tid, &path)) {
         PLOG(ERROR) << "Failed to find attribute '" << attr_name << "'";
         return false;
     }

     if (!WriteStringToFile(std::to_string(value), path)) {
         PLOG(ERROR) << "Failed to write '" << value << "' to " << path;
         return false;
     }
     return true;
 }

 bool setProcessGroupSwappiness(uid_t, int pid, int swappiness) {
     return SetProcessGroupValue(pid, "MemSwappiness", swappiness);
 }

 bool setProcessGroupSoftLimit(uid_t, int pid, int64_t soft_limit_in_bytes) {
     return SetProcessGroupValue(pid, "MemSoftLimit", soft_limit_in_bytes);
 }

 bool setProcessGroupLimit(uid_t, int pid, int64_t limit_in_bytes) {
     return SetProcessGroupValue(pid, "MemLimit", limit_in_bytes);
 }
	/*
	* Copyright 2014 Google, Inc
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	//#define LOG_NDEBUG 0
	#define LOG_TAG "libprocessgroup"

	#include <assert.h>
	#include <dirent.h>
	#include <errno.h>
	#include <fcntl.h>
	#include <inttypes.h>
	#include <signal.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <unistd.h>

	#include <chrono>
	#include <map>
	#include <memory>
	#include <mutex>
	#include <set>
	#include <string>
	#include <thread>

	#include <android-base/file.h>
	#include <android-base/logging.h>
	#include <android-base/properties.h>
	#include <android-base/stringprintf.h>
	#include <android-base/strings.h>
	#include <cutils/android_filesystem_config.h>
	#include <processgroup/processgroup.h>
	#include <task_profiles.h>

	using android::base::GetBoolProperty;
	using android::base::StartsWith;
	using android::base::StringPrintf;
	using android::base::WriteStringToFile;

	using namespace std::chrono_literals;

	#define PROCESSGROUP_CGROUP_PROCS_FILE "/cgroup.procs"

	bool CgroupGetControllerPath(const std::string& cgroup_name, std::string* path) {
	auto controller = CgroupMap::GetInstance().FindController(cgroup_name);

	if (!controller.HasValue()) {
	return false;
	}

	if (path) {
	*path = controller.path();
	}

	return true;
	}

	bool CgroupGetAttributePath(const std::string& attr_name, std::string* path) {
	const TaskProfiles& tp = TaskProfiles::GetInstance();
	const ProfileAttribute* attr = tp.GetAttribute(attr_name);

	if (attr == nullptr) {
	return false;
	}

	if (path) {
	*path = StringPrintf("%s/%s", attr->controller()->path(), attr->file_name().c_str());
	}

	return true;
	}

	bool CgroupGetAttributePathForTask(const std::string& attr_name, int tid, std::string* path) {
	const TaskProfiles& tp = TaskProfiles::GetInstance();
	const ProfileAttribute* attr = tp.GetAttribute(attr_name);

	if (attr == nullptr) {
	return false;
	}

	if (!attr->GetPathForTask(tid, path)) {
	PLOG(ERROR) << "Failed to find cgroup for tid " << tid;
	return false;
	}

	return true;
	}

	bool UsePerAppMemcg() {
	bool low_ram_device = GetBoolProperty("ro.config.low_ram", false);
	return GetBoolProperty("ro.config.per_app_memcg", low_ram_device);
	}

	static bool isMemoryCgroupSupported() {
	std::string cgroup_name;
	static bool memcg_supported = CgroupMap::GetInstance().FindController("memory").HasValue();

	return memcg_supported;
	}

	bool SetProcessProfiles(uid_t uid, pid_t pid, const std::vector<std::string>& profiles,
	bool use_fd_cache) {
	const TaskProfiles& tp = TaskProfiles::GetInstance();

	for (const auto& name : profiles) {
	TaskProfile* profile = tp.GetProfile(name);
	if (profile != nullptr) {
	if (use_fd_cache) {
	profile->EnableResourceCaching();
	}
	if (!profile->ExecuteForProcess(uid, pid)) {
	PLOG(WARNING) << "Failed to apply " << name << " process profile";
	}
	} else {
	PLOG(WARNING) << "Failed to find " << name << "process profile";
	}
	}

	return true;
	}

	bool SetTaskProfiles(int tid, const std::vector<std::string>& profiles, bool use_fd_cache) {
	const TaskProfiles& tp = TaskProfiles::GetInstance();

	for (const auto& name : profiles) {
	TaskProfile* profile = tp.GetProfile(name);
	if (profile != nullptr) {
	if (use_fd_cache) {
	profile->EnableResourceCaching();
	}
	if (!profile->ExecuteForTask(tid)) {
	PLOG(WARNING) << "Failed to apply " << name << " task profile";
	}
	} else {
	PLOG(WARNING) << "Failed to find " << name << "task profile";
	}
	}

	return true;
	}

	static std::string ConvertUidToPath(const char* cgroup, uid_t uid) {
	return StringPrintf("%s/uid_%d", cgroup, uid);
	}

	static std::string ConvertUidPidToPath(const char* cgroup, uid_t uid, int pid) {
	return StringPrintf("%s/uid_%d/pid_%d", cgroup, uid, pid);
	}

	static int RemoveProcessGroup(const char* cgroup, uid_t uid, int pid) {
	int ret;

	auto uid_pid_path = ConvertUidPidToPath(cgroup, uid, pid);
	ret = rmdir(uid_pid_path.c_str());

	auto uid_path = ConvertUidToPath(cgroup, uid);
	rmdir(uid_path.c_str());

	return ret;
	}

	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) {
	if (dir->d_type != DT_DIR) {
	continue;
	}

	if (!StartsWith(dir->d_name, "pid_")) {
	continue;
	}

	auto path = StringPrintf("%s/%s", uid_path.c_str(), dir->d_name);
	LOG(VERBOSE) << "Removing " << path;
	if (rmdir(path.c_str()) == -1) {
	if (errno != EBUSY) {
	PLOG(WARNING) << "Failed to remove " << path;
	}
	empty = false;
	}
	}
	}
	return empty;
	}

	void removeAllProcessGroups() {
	LOG(VERBOSE) << "removeAllProcessGroups()";

	std::vector<std::string> cgroups;
	std::string path;

	if (CgroupGetControllerPath("cpuacct", &path)) {
	cgroups.push_back(path);
	}
	if (CgroupGetControllerPath("memory", &path)) {
	cgroups.push_back(path + "/apps");
	}

	for (std::string cgroup_root_path : cgroups) {
	std::unique_ptr<DIR, decltype(&closedir)> root(opendir(cgroup_root_path.c_str()), closedir);
	if (root == NULL) {
	PLOG(ERROR) << "Failed to open " << cgroup_root_path;
	} else {
	dirent* dir;
	while ((dir = readdir(root.get())) != nullptr) {
	if (dir->d_type != DT_DIR) {
	continue;
	}

	if (!StartsWith(dir->d_name, "uid_")) {
	continue;
	}

	auto path = StringPrintf("%s/%s", cgroup_root_path.c_str(), dir->d_name);
	if (!RemoveUidProcessGroups(path)) {
	LOG(VERBOSE) << "Skip removing " << path;
	continue;
	}
	LOG(VERBOSE) << "Removing " << path;
	if (rmdir(path.c_str()) == -1 && errno != EBUSY) {
	PLOG(WARNING) << "Failed to remove " << path;
	}
	}
	}
	}
	}

	static bool MkdirAndChown(const std::string& path, mode_t mode, uid_t uid, gid_t gid) {
	if (mkdir(path.c_str(), mode) == -1 && errno != EEXIST) {
	return false;
	}

	if (chown(path.c_str(), uid, gid) == -1) {
	int saved_errno = errno;
	rmdir(path.c_str());
	errno = saved_errno;
	return false;
	}

	return true;
	}

	// Returns number of processes killed on success
	// Returns 0 if there are no processes in the process cgroup left to kill
	// Returns -1 on error
	static int DoKillProcessGroupOnce(const char* cgroup, uid_t uid, int initialPid, int signal) {
	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;
	}

	// We separate all of the pids in the cgroup into those pids that are also the leaders of
	// process groups (stored in the pgids set) and those that are not (stored in the pids set).
	std::set<pid_t> pgids;
	pgids.emplace(initialPid);
	std::set<pid_t> pids;

	pid_t pid;
	int processes = 0;
	while (fscanf(fd.get(), "%d\n", &pid) == 1 && pid >= 0) {
	processes++;
	if (pid == 0) {
	// Should never happen... but if it does, trying to kill this
	// will boomerang right back and kill us! Let's not let that happen.
	LOG(WARNING) << "Yikes, we've been told to kill pid 0! How about we don't do that?";
	continue;
	}
	pid_t pgid = getpgid(pid);
	if (pgid == -1) PLOG(ERROR) << "getpgid(" << pid << ") failed";
	if (pgid == pid) {
	pgids.emplace(pid);
	} else {
	pids.emplace(pid);
	}
	}

	// Erase all pids that will be killed when we kill the process groups.
	for (auto it = pids.begin(); it != pids.end();) {
	pid_t pgid = getpgid(*it);
	if (pgids.count(pgid) == 1) {
	it = pids.erase(it);
	} else {
	++it;
	}
	}

	// Kill all process groups.
	for (const auto pgid : pgids) {
	LOG(VERBOSE) << "Killing process group " << -pgid << " in uid " << uid
	<< " as part of process cgroup " << initialPid;

	if (kill(-pgid, signal) == -1 && errno != ESRCH) {
	PLOG(WARNING) << "kill(" << -pgid << ", " << signal << ") failed";
	}
	}

	// Kill remaining pids.
	for (const auto pid : pids) {
	LOG(VERBOSE) << "Killing pid " << pid << " in uid " << uid << " as part of process cgroup "
	<< initialPid;

	if (kill(pid, signal) == -1 && errno != ESRCH) {
	PLOG(WARNING) << "kill(" << pid << ", " << signal << ") failed";
	}
	}

	return feof(fd.get()) ? processes : -1;
	}

	static int KillProcessGroup(uid_t uid, int initialPid, int signal, int retries) {
	std::string cpuacct_path;
	std::string memory_path;

	CgroupGetControllerPath("cpuacct", &cpuacct_path);
	CgroupGetControllerPath("memory", &memory_path);
	memory_path += "/apps";

	const char* cgroup =
	(!access(ConvertUidPidToPath(cpuacct_path.c_str(), uid, initialPid).c_str(), F_OK))
	? cpuacct_path.c_str()
	: memory_path.c_str();

	std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();

	int retry = retries;
	int processes;
	while ((processes = DoKillProcessGroupOnce(cgroup, uid, initialPid, signal)) > 0) {
	LOG(VERBOSE) << "Killed " << processes << " processes for processgroup " << initialPid;
	if (retry > 0) {
	std::this_thread::sleep_for(5ms);
	--retry;
	} else {
	break;
	}
	}

	if (processes < 0) {
	PLOG(ERROR) << "Error encountered killing process cgroup uid " << uid << " pid "
	<< initialPid;
	return -1;
	}

	std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
	auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count();

	// We only calculate the number of 'processes' when killing the processes.
	// In the retries == 0 case, we only kill the processes once and therefore
	// will not have waited then recalculated how many processes are remaining
	// after the first signals have been sent.
	// Logging anything regarding the number of 'processes' here does not make sense.

	if (processes == 0) {
	if (retries > 0) {
	LOG(INFO) << "Successfully killed process cgroup uid " << uid << " pid " << initialPid
	<< " in " << static_cast<int>(ms) << "ms";
	}
	return RemoveProcessGroup(cgroup, uid, initialPid);
	} else {
	if (retries > 0) {
	LOG(ERROR) << "Failed to kill process cgroup uid " << uid << " pid " << initialPid
	<< " in " << static_cast<int>(ms) << "ms, " << processes
	<< " processes remain";
	}
	return -1;
	}
	}

	int killProcessGroup(uid_t uid, int initialPid, int signal) {
	return KillProcessGroup(uid, initialPid, signal, 40 /retries/);
	}

	int killProcessGroupOnce(uid_t uid, int initialPid, int signal) {
	return KillProcessGroup(uid, initialPid, signal, 0 /retries/);
	}

	int createProcessGroup(uid_t uid, int initialPid, bool memControl) {
	std::string cgroup;
	if (isMemoryCgroupSupported() && (memControl \|\| UsePerAppMemcg())) {
	CgroupGetControllerPath("memory", &cgroup);
	cgroup += "/apps";
	} else {
	CgroupGetControllerPath("cpuacct", &cgroup);
	}

	auto uid_path = ConvertUidToPath(cgroup.c_str(), uid);

	if (!MkdirAndChown(uid_path, 0750, AID_SYSTEM, AID_SYSTEM)) {
	PLOG(ERROR) << "Failed to make and chown " << uid_path;
	return -errno;
	}

	auto uid_pid_path = ConvertUidPidToPath(cgroup.c_str(), uid, initialPid);

	if (!MkdirAndChown(uid_pid_path, 0750, AID_SYSTEM, AID_SYSTEM)) {
	PLOG(ERROR) << "Failed to make and chown " << uid_pid_path;
	return -errno;
	}

	auto uid_pid_procs_file = uid_pid_path + PROCESSGROUP_CGROUP_PROCS_FILE;

	int ret = 0;
	if (!WriteStringToFile(std::to_string(initialPid), uid_pid_procs_file)) {
	ret = -errno;
	PLOG(ERROR) << "Failed to write '" << initialPid << "' to " << uid_pid_procs_file;
	}

	return ret;
	}

	static bool SetProcessGroupValue(int tid, const std::string& attr_name, int64_t value) {
	if (!isMemoryCgroupSupported()) {
	PLOG(ERROR) << "Memcg is not mounted.";
	return false;
	}

	std::string path;
	if (!CgroupGetAttributePathForTask(attr_name, tid, &path)) {
	PLOG(ERROR) << "Failed to find attribute '" << attr_name << "'";
	return false;
	}

	if (!WriteStringToFile(std::to_string(value), path)) {
	PLOG(ERROR) << "Failed to write '" << value << "' to " << path;
	return false;
	}
	return true;
	}

	bool setProcessGroupSwappiness(uid_t, int pid, int swappiness) {
	return SetProcessGroupValue(pid, "MemSwappiness", swappiness);
	}

	bool setProcessGroupSoftLimit(uid_t, int pid, int64_t soft_limit_in_bytes) {
	return SetProcessGroupValue(pid, "MemSoftLimit", soft_limit_in_bytes);
	}

	bool setProcessGroupLimit(uid_t, int pid, int64_t limit_in_bytes) {
	return SetProcessGroupValue(pid, "MemLimit", limit_in_bytes);
	}