From da9b6bb196e0165342a414657edfc5aaf165baa5 Mon Sep 17 00:00:00 2001 From: Laurent Pinchart Date: Fri, 2 Jul 2021 01:30:41 +0300 Subject: base: thread: Fix recursive calls to dispatchMessages() There are use cases for calling the dispatchMessages() function recursively, from within a message handler. This can be used, for instance, to force delivery of messages posted to a thread concurrently to stopping the thread. This currently causes access, in the outer dispatchMessages() call, to iterators that have been invalidated by erasing list elements in the recursive call, leading to undefined behaviour (most likely double-free or other crashes). Fix it by only erasing messages from the list at the end of the outer call, identified using a recursion counter. Bug: https://bugs.libcamera.org/show_bug.cgi?id=26 Signed-off-by: Laurent Pinchart Reviewed-by: Jacopo Mondi Tested-by: David Plowman Reviewed-by: Kieran Bingham --- src/libcamera/base/thread.cpp | 43 +++++++++++++++++++++++++++++++++---------- 1 file changed, 33 insertions(+), 10 deletions(-) (limited to 'src') diff --git a/src/libcamera/base/thread.cpp b/src/libcamera/base/thread.cpp index 7f791152..1232f895 100644 --- a/src/libcamera/base/thread.cpp +++ b/src/libcamera/base/thread.cpp @@ -126,6 +126,11 @@ public: * \brief Protects the \ref list_ */ Mutex mutex_; + /** + * \brief The recursion level for recursive Thread::dispatchMessages() + * calls + */ + unsigned int recursion_ = 0; }; /** @@ -595,30 +600,34 @@ void Thread::removeMessages(Object *receiver) * Messages shall only be dispatched from the current thread, typically within * the thread from the run() function. Calling this function outside of the * thread results in undefined behaviour. + * + * This function is not thread-safe, but it may be called recursively in the + * same thread from an object's message handler. It guarantees delivery of + * messages in the order they have been posted in all cases. */ void Thread::dispatchMessages(Message::Type type) { ASSERT(data_ == ThreadData::current()); + ++data_->messages_.recursion_; + MutexLocker locker(data_->messages_.mutex_); std::list> &messages = data_->messages_.list_; - for (auto iter = messages.begin(); iter != messages.end(); ) { - std::unique_ptr &msg = *iter; - - if (!msg) { - iter = data_->messages_.list_.erase(iter); + for (std::unique_ptr &msg : messages) { + if (!msg) continue; - } - if (type != Message::Type::None && msg->type() != type) { - ++iter; + if (type != Message::Type::None && msg->type() != type) continue; - } + /* + * Move the message, setting the entry in the list to null. It + * will cause recursive calls to ignore the entry, and the erase + * loop at the end of the function to delete it from the list. + */ std::unique_ptr message = std::move(msg); - iter = data_->messages_.list_.erase(iter); Object *receiver = message->receiver_; ASSERT(data_ == receiver->thread()->data_); @@ -629,6 +638,20 @@ void Thread::dispatchMessages(Message::Type type) message.reset(); locker.lock(); } + + /* + * If the recursion level is 0, erase all null messages in the list. We + * can't do so during recursion, as it would invalidate the iterator of + * the outer calls. + */ + if (!--data_->messages_.recursion_) { + for (auto iter = messages.begin(); iter != messages.end(); ) { + if (!*iter) + iter = messages.erase(iter); + else + ++iter; + } + } } /** -- cgit v1.2.1