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Fix Deadlock Issue On AppFuseBridge

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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

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.

Signed-off-by: hyeeun.jun@samsung.com <hyeeun.jun@samsung.com>
Bug: https://issuetracker.google.com/issues/145707568
Bug: 157535024
Test: atest --test-mapping apex/blobstore

Change-Id: I0ab002da9a0b7ca2f518d50ab477a080cabe3788
This commit is contained in:
hyeeun.jun@samsung.com 2020-01-29 17:10:17 +09:00 • committed by Narayan Kamath
parent c39f708cb4
commit 612fc47090
2 changed files with 17 additions and 3 deletions
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14
libappfuse/FuseBridgeLoop.cc
View file

@ -311,6 +311,8 @@ class BridgeEpollController : private EpollController {
}
};
std::recursive_mutex FuseBridgeLoop::mutex_;
FuseBridgeLoop::FuseBridgeLoop() : opened_(true) {
base::unique_fd epoll_fd(epoll_create1(EPOLL_CLOEXEC));
if (epoll_fd.get() == -1) {
@ -328,7 +330,7 @@ bool FuseBridgeLoop::AddBridge(int mount_id, base::unique_fd dev_fd, base::uniqu
std::unique_ptr<FuseBridgeEntry> bridge(
new FuseBridgeEntry(mount_id, std::move(dev_fd), std::move(proxy_fd)));
std::lock_guard<std::mutex> lock(mutex_);
std::lock_guard<std::recursive_mutex> lock(mutex_);
if (!opened_) {
LOG(ERROR) << "Tried to add a mount to a closed bridge";
return false;
@ -372,7 +374,7 @@ void FuseBridgeLoop::Start(FuseBridgeLoopCallback* callback) {
const bool wait_result = epoll_controller_->Wait(bridges_.size(), &entries);
LOG(VERBOSE) << "Receive epoll events";
{
std::lock_guard<std::mutex> lock(mutex_);
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());
@ -385,5 +387,13 @@ void FuseBridgeLoop::Start(FuseBridgeLoopCallback* callback) {
}
}
void FuseBridgeLoop::Lock() {
mutex_.lock();
}
void FuseBridgeLoop::Unlock() {
mutex_.unlock();
}
} // namespace fuse
} // namespace android

6
libappfuse/include/libappfuse/FuseBridgeLoop.h
View file

@ -50,6 +50,10 @@ class FuseBridgeLoop final {
// thread from one which invokes |Start|.
bool AddBridge(int mount_id, base::unique_fd dev_fd, base::unique_fd proxy_fd);
static void Lock();
static void Unlock();
private:
bool ProcessEventLocked(const std::unordered_set<FuseBridgeEntry*>& entries,
FuseBridgeLoopCallback* callback);
@ -60,7 +64,7 @@ class FuseBridgeLoop final {
std::map<int, std::unique_ptr<FuseBridgeEntry>> bridges_;
// Lock for multi-threading.
std::mutex mutex_;
static std::recursive_mutex mutex_;
bool opened_;