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Commit 612fc470 authored by hyeeun.jun@samsung.com's avatar hyeeun.jun@samsung.com Committed by Narayan Kamath
Browse files

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

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: default avatarhyeeun.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
parent c39f708c

libappfuse/FuseBridgeLoop.cc

+12 −2
Original line number Diff line number Diff line
@@ -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

libappfuse/include/libappfuse/FuseBridgeLoop.h

+5 −1
Original line number Diff line number Diff line
@@ -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_;