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platform_system_core/libappfuse/FuseBridgeLoop.cc
hyeeun.jun@samsung.com 49545ab897 Fix Deadlock Issue On AppFuseBridge 
There are two locks used by AppFuseBridge.
First is it's object lock, and the second is a mutex lock in app fuse library.
There are two oppsite routines to get those locks.

  (Thread A) Got Java lock -> Try to get Native lock
  (Thread B)        Got Native lock -> Try to get Java lock

Bug : https://issuetracker.google.com/issues/145707568
Signed-off-by: hyeeun.jun@samsung.com <hyeeun.jun@samsung.com>

The order must be followed to obtain two locks.
If not, the dead lock will be caused.
Therefore we change the routine to get the mutex lock first, and the object lock later.
2020-02-18 04:33:06 +00:00

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/*
* Copyright (C) 2016 The Android Open Source Project
*
* 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 specic language governing permissions and
* limitations under the License.
*/
#include "libappfuse/FuseBridgeLoop.h"
#include <sys/epoll.h>
#include <sys/socket.h>
#include <unordered_map>
#include <android-base/logging.h>
#include <android-base/unique_fd.h>
#include "libappfuse/EpollController.h"
namespace android {
namespace fuse {
namespace {
enum class FuseBridgeState { kWaitToReadEither, kWaitToReadProxy, kWaitToWriteProxy, kClosing };
struct FuseBridgeEntryEvent {
FuseBridgeEntry* entry;
int events;
};
void GetObservedEvents(FuseBridgeState state, int* device_events, int* proxy_events) {
switch (state) {
case FuseBridgeState::kWaitToReadEither:
*device_events = EPOLLIN;
*proxy_events = EPOLLIN;
return;
case FuseBridgeState::kWaitToReadProxy:
*device_events = 0;
*proxy_events = EPOLLIN;
return;
case FuseBridgeState::kWaitToWriteProxy:
*device_events = 0;
*proxy_events = EPOLLOUT;
return;
case FuseBridgeState::kClosing:
*device_events = 0;
*proxy_events = 0;
return;
}
}
void LogResponseError(const std::string& message, const FuseResponse& response) {
LOG(ERROR) << message << ": header.len=" << response.header.len
<< " header.error=" << response.header.error
<< " header.unique=" << response.header.unique;
}
}
class FuseBridgeEntry {
public:
FuseBridgeEntry(int mount_id, base::unique_fd&& dev_fd, base::unique_fd&& proxy_fd)
: mount_id_(mount_id),
device_fd_(std::move(dev_fd)),
proxy_fd_(std::move(proxy_fd)),
state_(FuseBridgeState::kWaitToReadEither),
last_state_(FuseBridgeState::kWaitToReadEither),
last_device_events_({this, 0}),
last_proxy_events_({this, 0}),
open_count_(0) {}
// Transfer bytes depends on availability of FDs and the internal |state_|.
void Transfer(FuseBridgeLoopCallback* callback) {
constexpr int kUnexpectedEventMask = ~(EPOLLIN | EPOLLOUT);
const bool unexpected_event = (last_device_events_.events & kUnexpectedEventMask) ||
(last_proxy_events_.events & kUnexpectedEventMask);
const bool device_read_ready = last_device_events_.events & EPOLLIN;
const bool proxy_read_ready = last_proxy_events_.events & EPOLLIN;
const bool proxy_write_ready = last_proxy_events_.events & EPOLLOUT;
last_state_ = state_;
last_device_events_.events = 0;
last_proxy_events_.events = 0;
LOG(VERBOSE) << "Transfer device_read_ready=" << device_read_ready
<< " proxy_read_ready=" << proxy_read_ready
<< " proxy_write_ready=" << proxy_write_ready;
if (unexpected_event) {
LOG(ERROR) << "Invalid epoll event is observed";
state_ = FuseBridgeState::kClosing;
return;
}
switch (state_) {
case FuseBridgeState::kWaitToReadEither:
if (proxy_read_ready) {
state_ = ReadFromProxy();
} else if (device_read_ready) {
state_ = ReadFromDevice(callback);
}
return;
case FuseBridgeState::kWaitToReadProxy:
CHECK(proxy_read_ready);
state_ = ReadFromProxy();
return;
case FuseBridgeState::kWaitToWriteProxy:
CHECK(proxy_write_ready);
state_ = WriteToProxy();
return;
case FuseBridgeState::kClosing:
return;
}
}
bool IsClosing() const { return state_ == FuseBridgeState::kClosing; }
int mount_id() const { return mount_id_; }
private:
friend class BridgeEpollController;
FuseBridgeState ReadFromProxy() {
switch (buffer_.response.ReadOrAgain(proxy_fd_)) {
case ResultOrAgain::kSuccess:
break;
case ResultOrAgain::kFailure:
return FuseBridgeState::kClosing;
case ResultOrAgain::kAgain:
return FuseBridgeState::kWaitToReadProxy;
}
if (!buffer_.response.Write(device_fd_)) {
LogResponseError("Failed to write a reply from proxy to device", buffer_.response);
return FuseBridgeState::kClosing;
}
auto it = opcode_map_.find(buffer_.response.header.unique);
if (it != opcode_map_.end()) {
switch (it->second) {
case FUSE_OPEN:
if (buffer_.response.header.error == fuse::kFuseSuccess) {
open_count_++;
}
break;
case FUSE_RELEASE:
if (open_count_ > 0) {
open_count_--;
} else {
LOG(WARNING) << "Unexpected FUSE_RELEASE before opening a file.";
break;
}
if (open_count_ == 0) {
return FuseBridgeState::kClosing;
}
break;
}
opcode_map_.erase(it);
}
return FuseBridgeState::kWaitToReadEither;
}
FuseBridgeState ReadFromDevice(FuseBridgeLoopCallback* callback) {
LOG(VERBOSE) << "ReadFromDevice";
if (!buffer_.request.Read(device_fd_)) {
return FuseBridgeState::kClosing;
}
const uint32_t opcode = buffer_.request.header.opcode;
const uint64_t unique = buffer_.request.header.unique;
LOG(VERBOSE) << "Read a fuse packet, opcode=" << opcode << " unique=" << unique;
if (unique == 0) {
return FuseBridgeState::kWaitToReadEither;
}
switch (opcode) {
case FUSE_FORGET:
// Do not reply to FUSE_FORGET.
return FuseBridgeState::kWaitToReadEither;
case FUSE_LOOKUP:
case FUSE_GETATTR:
case FUSE_OPEN:
case FUSE_READ:
case FUSE_WRITE:
case FUSE_RELEASE:
case FUSE_FSYNC:
if (opcode == FUSE_OPEN || opcode == FUSE_RELEASE) {
opcode_map_.emplace(buffer_.request.header.unique, opcode);
}
return WriteToProxy();
case FUSE_INIT:
buffer_.HandleInit();
break;
default:
buffer_.HandleNotImpl();
break;
}
if (!buffer_.response.Write(device_fd_)) {
LogResponseError("Failed to write a response to device", buffer_.response);
return FuseBridgeState::kClosing;
}
if (opcode == FUSE_INIT) {
callback->OnMount(mount_id_);
}
return FuseBridgeState::kWaitToReadEither;
}
FuseBridgeState WriteToProxy() {
switch (buffer_.request.WriteOrAgain(proxy_fd_)) {
case ResultOrAgain::kSuccess:
return FuseBridgeState::kWaitToReadEither;
case ResultOrAgain::kFailure:
LOG(ERROR) << "Failed to write a request to proxy:"
<< " header.len=" << buffer_.request.header.len
<< " header.opcode=" << buffer_.request.header.opcode
<< " header.unique=" << buffer_.request.header.unique
<< " header.nodeid=" << buffer_.request.header.nodeid;
return FuseBridgeState::kClosing;
case ResultOrAgain::kAgain:
return FuseBridgeState::kWaitToWriteProxy;
}
}
const int mount_id_;
base::unique_fd device_fd_;
base::unique_fd proxy_fd_;
FuseBuffer buffer_;
FuseBridgeState state_;
FuseBridgeState last_state_;
FuseBridgeEntryEvent last_device_events_;
FuseBridgeEntryEvent last_proxy_events_;
// Remember map between unique and opcode in fuse_in_header so that we can
// refer the opcode later.
std::unordered_map<uint64_t, uint32_t> opcode_map_;
int open_count_;
DISALLOW_COPY_AND_ASSIGN(FuseBridgeEntry);
};
class BridgeEpollController : private EpollController {
public:
BridgeEpollController(base::unique_fd&& poll_fd) : EpollController(std::move(poll_fd)) {}
bool AddBridgePoll(FuseBridgeEntry* bridge) const {
return InvokeControl(EPOLL_CTL_ADD, bridge);
}
bool UpdateOrDeleteBridgePoll(FuseBridgeEntry* bridge) const {
return InvokeControl(
bridge->state_ != FuseBridgeState::kClosing ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, bridge);
}
bool Wait(size_t bridge_count, std::unordered_set<FuseBridgeEntry*>* entries_out) {
CHECK(entries_out);
const size_t event_count = std::max<size_t>(bridge_count * 2, 1);
if (!EpollController::Wait(event_count)) {
return false;
}
entries_out->clear();
for (const auto& event : events()) {
FuseBridgeEntryEvent* const entry_event =
reinterpret_cast<FuseBridgeEntryEvent*>(event.data.ptr);
entry_event->events = event.events;
entries_out->insert(entry_event->entry);
}
return true;
}
private:
bool InvokeControl(int op, FuseBridgeEntry* bridge) const {
LOG(VERBOSE) << "InvokeControl op=" << op << " bridge=" << bridge->mount_id_
<< " state=" << static_cast<int>(bridge->state_)
<< " last_state=" << static_cast<int>(bridge->last_state_);
int last_device_events;
int last_proxy_events;
int device_events;
int proxy_events;
GetObservedEvents(bridge->last_state_, &last_device_events, &last_proxy_events);
GetObservedEvents(bridge->state_, &device_events, &proxy_events);
bool result = true;
if (op != EPOLL_CTL_MOD || last_device_events != device_events) {
result &= EpollController::InvokeControl(op, bridge->device_fd_, device_events,
&bridge->last_device_events_);
}
if (op != EPOLL_CTL_MOD || last_proxy_events != proxy_events) {
result &= EpollController::InvokeControl(op, bridge->proxy_fd_, proxy_events,
&bridge->last_proxy_events_);
}
return result;
}
};
std::recursive_mutex FuseBridgeLoop::mutex_;
FuseBridgeLoop::FuseBridgeLoop() : opened_(true) {
base::unique_fd epoll_fd(epoll_create1(EPOLL_CLOEXEC));
if (epoll_fd.get() == -1) {
PLOG(ERROR) << "Failed to open FD for epoll";
opened_ = false;
return;
}
epoll_controller_.reset(new BridgeEpollController(std::move(epoll_fd)));
}
FuseBridgeLoop::~FuseBridgeLoop() { CHECK(bridges_.empty()); }
bool FuseBridgeLoop::AddBridge(int mount_id, base::unique_fd dev_fd, base::unique_fd proxy_fd) {
LOG(VERBOSE) << "Adding bridge " << mount_id;
std::unique_ptr<FuseBridgeEntry> bridge(
new FuseBridgeEntry(mount_id, std::move(dev_fd), std::move(proxy_fd)));
std::lock_guard<std::recursive_mutex> lock(mutex_);
if (!opened_) {
LOG(ERROR) << "Tried to add a mount to a closed bridge";
return false;
}
if (bridges_.count(mount_id)) {
LOG(ERROR) << "Tried to add a mount point that has already been added";
return false;
}
if (!epoll_controller_->AddBridgePoll(bridge.get())) {
return false;
}
bridges_.emplace(mount_id, std::move(bridge));
return true;
}
bool FuseBridgeLoop::ProcessEventLocked(const std::unordered_set<FuseBridgeEntry*>& entries,
FuseBridgeLoopCallback* callback) {
for (auto entry : entries) {
entry->Transfer(callback);
if (!epoll_controller_->UpdateOrDeleteBridgePoll(entry)) {
return false;
}
if (entry->IsClosing()) {
const int mount_id = entry->mount_id();
bridges_.erase(mount_id);
callback->OnClosed(mount_id);
if (bridges_.size() == 0) {
// All bridges are now closed.
return false;
}
}
}
return true;
}
void FuseBridgeLoop::Start(FuseBridgeLoopCallback* callback) {
LOG(DEBUG) << "Start fuse bridge loop";
std::unordered_set<FuseBridgeEntry*> entries;
while (true) {
const bool wait_result = epoll_controller_->Wait(bridges_.size(), &entries);
LOG(VERBOSE) << "Receive epoll events";
{
std::lock_guard<std::recursive_mutex> lock(mutex_);
if (!(wait_result && ProcessEventLocked(entries, callback))) {
for (auto it = bridges_.begin(); it != bridges_.end();) {
callback->OnClosed(it->second->mount_id());
it = bridges_.erase(it);
}
opened_ = false;
return;
}
}
}
}
void FuseBridgeLoop::Lock() {
mutex_.lock();
}
void FuseBridgeLoop::Unlock() {
mutex_.unlock();
}
} // namespace fuse
} // namespace android
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