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ueventd: parallelize uevent handling 

fork() subprocesses to handle uevents in parallel.

This reduces coldboot time on bullhead from ~446ms to ~230ms.
This reduces coldboot time on sailfish from ~690ms to ~360ms.
This reduces coldboot time on ryu from ~187ms to ~122ms.

Bug: 33785894

Test: boot bullhead x40, observe no major differences in /dev and /sys
Test: boot sailfish x40, observe no major differences in /dev and /sys
Test: boot ryu x40, observe no major differences in /dev and /sys
Test: boottime tests on bullhead and sailfish
Test: init unit tests

Change-Id: Ie2f63e000b8af78d187477d31fe109f20304d749
This commit is contained in:
Tom Cherry 2017-05-16 15:35:41 -07:00
parent 28c11dcff4
commit c583305ed7
6 changed files with 238 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
init/devices.cpp
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@ -175,7 +175,7 @@ void DeviceHandler::FixupSysPermissions(const std::string& upath,
if (s.MatchWithSubsystem(path, subsystem)) s.SetPermissions(path);
}
if (access(path.c_str(), F_OK) == 0) {
if (!skip_restorecon_ && access(path.c_str(), F_OK) == 0) {
LOG(VERBOSE) << "restorecon_recursive: " << path;
if (selinux_android_restorecon(path.c_str(), SELINUX_ANDROID_RESTORECON_RECURSE) != 0) {
PLOG(ERROR) << "selinux_android_restorecon(" << path << ") failed";
@ -467,12 +467,13 @@ void DeviceHandler::HandleDeviceEvent(const Uevent& uevent) {
DeviceHandler::DeviceHandler(std::vector<Permissions> dev_permissions,
std::vector<SysfsPermissions> sysfs_permissions,
std::vector<Subsystem> subsystems)
std::vector<Subsystem> subsystems, bool skip_restorecon)
: dev_permissions_(std::move(dev_permissions)),
sysfs_permissions_(std::move(sysfs_permissions)),
subsystems_(std::move(subsystems)),
sehandle_(selinux_android_file_context_handle()) {}
sehandle_(selinux_android_file_context_handle()),
skip_restorecon_(skip_restorecon) {}
DeviceHandler::DeviceHandler()
: DeviceHandler(std::vector<Permissions>{}, std::vector<SysfsPermissions>{},
std::vector<Subsystem>{}) {}
std::vector<Subsystem>{}, false) {}

15
init/devices.h
View File

@ -114,14 +114,21 @@ class DeviceHandler {
DeviceHandler();
DeviceHandler(std::vector<Permissions> dev_permissions,
std::vector<SysfsPermissions> sysfs_permissions,
std::vector<Subsystem> subsystems);
std::vector<Subsystem> subsystems, bool skip_restorecon);
~DeviceHandler(){};
void HandleDeviceEvent(const Uevent& uevent);
void FixupSysPermissions(const std::string& upath, const std::string& subsystem) const;
void HandlePlatformDeviceEvent(const Uevent& uevent);
void HandleBlockDeviceEvent(const Uevent& uevent) const;
void HandleGenericDeviceEvent(const Uevent& uevent) const;
std::vector<std::string> GetBlockDeviceSymlinks(const Uevent& uevent) const;
void set_skip_restorecon(bool value) { skip_restorecon_ = value; }
private:
void FixupSysPermissions(const std::string& upath, const std::string& subsystem) const;
std::tuple<mode_t, uid_t, gid_t> GetDevicePermissions(
const std::string& path, const std::vector<std::string>& links) const;
void MakeDevice(const std::string& path, int block, int major, int minor,
@ -129,15 +136,13 @@ class DeviceHandler {
std::vector<std::string> GetCharacterDeviceSymlinks(const Uevent& uevent) const;
void HandleDevice(const std::string& action, const std::string& devpath, int block, int major,
int minor, const std::vector<std::string>& links) const;
void HandlePlatformDeviceEvent(const Uevent& uevent);
void HandleBlockDeviceEvent(const Uevent& uevent) const;
void HandleGenericDeviceEvent(const Uevent& uevent) const;
std::vector<Permissions> dev_permissions_;
std::vector<SysfsPermissions> sysfs_permissions_;
std::vector<Subsystem> subsystems_;
PlatformDeviceList platform_devices_;
selabel_handle* sehandle_;
bool skip_restorecon_;
};
// Exposed for testing

30
init/firmware_handler.cpp
View File

@ -18,6 +18,7 @@
#include <fcntl.h>
#include <sys/sendfile.h>
#include <sys/wait.h>
#include <unistd.h>
#include <string>
@ -103,14 +104,29 @@ void HandleFirmwareEvent(const Uevent& uevent) {
if (uevent.subsystem != "firmware" || uevent.action != "add") return;
// Loading the firmware in a child means we can do that in parallel...
// (We ignore SIGCHLD rather than wait for our children.)
// We double fork instead of waiting for these processes.
pid_t pid = fork();
if (pid == 0) {
Timer t;
ProcessFirmwareEvent(uevent);
LOG(INFO) << "loading " << uevent.path << " took " << t;
_exit(EXIT_SUCCESS);
} else if (pid == -1) {
if (pid == -1) {
PLOG(ERROR) << "could not fork to process firmware event for " << uevent.firmware;
return;
}
if (pid == 0) {
pid = fork();
if (pid == -1) {
PLOG(ERROR) << "could not fork a sceond time to process firmware event for "
<< uevent.firmware;
_exit(EXIT_FAILURE);
}
if (pid == 0) {
Timer t;
ProcessFirmwareEvent(uevent);
LOG(INFO) << "loading " << uevent.path << " took " << t;
_exit(EXIT_SUCCESS);
}
_exit(EXIT_SUCCESS);
}
waitpid(pid, nullptr, 0);
}

2
init/uevent_listener.cpp
View File

@ -165,7 +165,7 @@ RegenerationAction UeventListener::RegenerateUeventsForPath(const std::string& p
return RegenerateUeventsForDir(d.get(), callback);
}
static const char* kRegenerationPaths[] = {"/sys/class", "/sys/block", "/sys/devices"};
const char* kRegenerationPaths[] = {"/sys/class", "/sys/block", "/sys/devices"};
void UeventListener::RegenerateUevents(RegenerateCallback callback) const {
for (const auto path : kRegenerationPaths) {

2
init/uevent_listener.h
View File

@ -35,6 +35,8 @@ enum class RegenerationAction {
using RegenerateCallback = std::function<RegenerationAction(const Uevent&)>;
using PollCallback = std::function<void(const Uevent&)>;
extern const char* kRegenerationPaths[3];
class UeventListener {
public:
UeventListener();

217
init/ueventd.cpp
View File

@ -22,10 +22,15 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <set>
#include <thread>
#include <android-base/logging.h>
#include <android-base/properties.h>
#include <android-base/stringprintf.h>
#include <selinux/android.h>
#include <selinux/selinux.h>
#include "devices.h"
@ -35,6 +40,194 @@
#include "ueventd_parser.h"
#include "util.h"
// At a high level, ueventd listens for uevent messages generated by the kernel through a netlink
// socket. When ueventd receives such a message it handles it by taking appropriate actions,
// which can typically be creating a device node in /dev, setting file permissions, setting selinux
// labels, etc.
// Ueventd also handles loading of firmware that the kernel requests, and creates symlinks for block
// and character devices.
// When ueventd starts, it regenerates uevents for all currently registered devices by traversing
// /sys and writing 'add' to each 'uevent' file that it finds. This causes the kernel to generate
// and resend uevent messages for all of the currently registered devices. This is done, because
// ueventd would not have been running when these devices were registered and therefore was unable
// to receive their uevent messages and handle them appropriately. This process is known as
// 'cold boot'.
// 'init' currently waits synchronously on the cold boot process of ueventd before it continues
// its boot process. For this reason, cold boot should be as quick as possible. One way to achieve
// a speed up here is to parallelize the handling of ueventd messages, which consume the bulk of the
// time during cold boot.
// Handling of uevent messages has two unique properties:
// 1) It can be done in isolation; it doesn't need to read or write any status once it is started.
// 2) It uses setegid() and setfscreatecon() so either care (aka locking) must be taken to ensure
// that no file system operations are done while the uevent process has an abnormal egid or
// fscreatecon or this handling must happen in a separate process.
// Given the above two properties, it is best to fork() subprocesses to handle the uevents. This
// reduces the overhead and complexity that would be required in a solution with threads and locks.
// In testing, a racy multithreaded solution has the same performance as the fork() solution, so
// there is no reason to deal with the complexity of the former.
// One other important caveat during the boot process is the handling of SELinux restorecon.
// Since many devices have child devices, calling selinux_android_restorecon() recursively for each
// device when its uevent is handled, results in multiple restorecon operations being done on a
// given file. It is more efficient to simply do restorecon recursively on /sys during cold boot,
// than to do restorecon on each device as its uevent is handled. This only applies to cold boot;
// once that has completed, restorecon is done for each device as its uevent is handled.
// With all of the above considered, the cold boot process has the below steps:
// 1) ueventd regenerates uevents by doing the /sys traversal and listens to the netlink socket for
// the generated uevents. It writes these uevents into a queue represented by a vector.
//
// 2) ueventd forks 'n' separate uevent handler subprocesses and has each of them to handle the
// uevents in the queue based on a starting offset (their process number) and a stride (the total
// number of processes). Note that no IPC happens at this point and only const functions from
// DeviceHandler should be called from this context.
//
// 3) In parallel to the subprocesses handling the uevents, the main thread of ueventd calls
// selinux_android_restorecon() recursively on /sys/class, /sys/block, and /sys/devices.
//
// 4) Once the restorecon operation finishes, the main thread calls waitpid() to wait for all
// subprocess handlers to complete and exit. Once this happens, it marks coldboot as having
// completed.
//
// At this point, ueventd is single threaded, poll()'s and then handles any future uevents.
// Lastly, it should be noted that uevents that occur during the coldboot process are handled
// without issue after the coldboot process completes. This is because the uevent listener is
// paused while the uevent handler and restorecon actions take place. Once coldboot completes,
// the uevent listener resumes in polling mode and will handle the uevents that occurred during
// coldboot.
class ColdBoot {
public:
ColdBoot(UeventListener& uevent_listener, DeviceHandler& device_handler)
: uevent_listener_(uevent_listener),
device_handler_(device_handler),
num_handler_subprocesses_(std::thread::hardware_concurrency() ?: 4) {}
void Run();
private:
void UeventHandlerMain(unsigned int process_num, unsigned int total_processes);
void RegenerateUevents();
void ForkSubProcesses();
void DoRestoreCon();
void WaitForSubProcesses();
UeventListener& uevent_listener_;
DeviceHandler& device_handler_;
unsigned int num_handler_subprocesses_;
std::vector<Uevent> uevent_queue_;
std::set<pid_t> subprocess_pids_;
};
void ColdBoot::UeventHandlerMain(unsigned int process_num, unsigned int total_processes) {
for (unsigned int i = process_num; i < uevent_queue_.size(); i += total_processes) {
auto& uevent = uevent_queue_[i];
if (uevent.action == "add" || uevent.action == "change" || uevent.action == "online") {
device_handler_.FixupSysPermissions(uevent.path, uevent.subsystem);
}
if (uevent.subsystem == "block") {
device_handler_.HandleBlockDeviceEvent(uevent);
} else {
device_handler_.HandleGenericDeviceEvent(uevent);
}
}
_exit(EXIT_SUCCESS);
}
void ColdBoot::RegenerateUevents() {
uevent_listener_.RegenerateUevents([this](const Uevent& uevent) {
HandleFirmwareEvent(uevent);
// This is the one mutable part of DeviceHandler, in which platform devices are
// added to a vector for later reference. Since there is no communication after
// fork()'ing subprocess handlers, all platform devices must be in the vector before
// we fork, and therefore they must be handled in this loop.
if (uevent.subsystem == "platform") {
device_handler_.HandlePlatformDeviceEvent(uevent);
}
uevent_queue_.emplace_back(std::move(uevent));
return RegenerationAction::kContinue;
});
}
void ColdBoot::ForkSubProcesses() {
for (unsigned int i = 0; i < num_handler_subprocesses_; ++i) {
auto pid = fork();
if (pid < 0) {
PLOG(FATAL) << "fork() failed!";
}
if (pid == 0) {
UeventHandlerMain(i, num_handler_subprocesses_);
}
subprocess_pids_.emplace(pid);
}
}
void ColdBoot::DoRestoreCon() {
for (const char* path : kRegenerationPaths) {
selinux_android_restorecon(path, SELINUX_ANDROID_RESTORECON_RECURSE);
}
device_handler_.set_skip_restorecon(false);
}
void ColdBoot::WaitForSubProcesses() {
// Treat subprocesses that crash or get stuck the same as if ueventd itself has crashed or gets
// stuck.
//
// When a subprocess crashes, we fatally abort from ueventd. init will restart ueventd when
// init reaps it, and the cold boot process will start again. If this continues to fail, then
// since ueventd is marked as a critical service, init will reboot to recovery.
//
// When a subprocess gets stuck, keep ueventd spinning waiting for it. init has a timeout for
// cold boot and will reboot to the bootloader if ueventd does not complete in time.
while (!subprocess_pids_.empty()) {
int status;
pid_t pid = TEMP_FAILURE_RETRY(waitpid(-1, &status, 0));
if (pid == -1) {
PLOG(ERROR) << "waitpid() failed";
continue;
}
auto it = std::find(subprocess_pids_.begin(), subprocess_pids_.end(), pid);
if (it == subprocess_pids_.end()) continue;
if (WIFEXITED(status)) {
if (WEXITSTATUS(status) == EXIT_SUCCESS) {
subprocess_pids_.erase(it);
} else {
LOG(FATAL) << "subprocess exited with status " << WEXITSTATUS(status);
}
} else if (WIFSIGNALED(status)) {
LOG(FATAL) << "subprocess killed by signal " << WTERMSIG(status);
}
}
}
void ColdBoot::Run() {
Timer cold_boot_timer;
RegenerateUevents();
ForkSubProcesses();
DoRestoreCon();
WaitForSubProcesses();
close(open(COLDBOOT_DONE, O_WRONLY | O_CREAT | O_CLOEXEC, 0000));
LOG(INFO) << "Coldboot took " << cold_boot_timer;
}
DeviceHandler CreateDeviceHandler() {
Parser parser;
@ -64,11 +257,10 @@ DeviceHandler CreateDeviceHandler() {
parser.ParseConfig("/ueventd." + hardware + ".rc");
return DeviceHandler(std::move(dev_permissions), std::move(sysfs_permissions),
std::move(subsystems));
std::move(subsystems), true);
}
int ueventd_main(int argc, char **argv)
{
int ueventd_main(int argc, char** argv) {
/*
* init sets the umask to 077 for forked processes. We need to
* create files with exact permissions, without modification by
@ -76,13 +268,6 @@ int ueventd_main(int argc, char **argv)
*/
umask(000);
/* Prevent fire-and-forget children from becoming zombies.
* If we should need to wait() for some children in the future
* (as opposed to none right now), double-forking here instead
* of ignoring SIGCHLD may be the better solution.
*/
signal(SIGCHLD, SIG_IGN);
InitKernelLogging(argv);
LOG(INFO) << "ueventd started!";
@ -95,16 +280,8 @@ int ueventd_main(int argc, char **argv)
UeventListener uevent_listener;
if (access(COLDBOOT_DONE, F_OK) != 0) {
Timer t;
uevent_listener.RegenerateUevents([&device_handler](const Uevent& uevent) {
HandleFirmwareEvent(uevent);
device_handler.HandleDeviceEvent(uevent);
return RegenerationAction::kContinue;
});
close(open(COLDBOOT_DONE, O_WRONLY | O_CREAT | O_CLOEXEC, 0000));
LOG(INFO) << "Coldboot took " << t;
ColdBoot cold_boot(uevent_listener, device_handler);
cold_boot.Run();
}
uevent_listener.DoPolling([&device_handler](const Uevent& uevent) {