[{"id":3156,"web_url":"https://patchwork.libcamera.org/comment/3156/","msgid":"<20191127150845.GH12879@bigcity.dyn.berto.se>","date":"2019-11-27T15:08:45","subject":"Re: [libcamera-devel] [PATCH 3/5] libcamera: thread: Fix race\n\tcondition when dispatching messages","submitter":{"id":5,"url":"https://patchwork.libcamera.org/api/people/5/","name":"Niklas Söderlund","email":"niklas.soderlund@ragnatech.se"},"content":"Hi Laurent,\n\nThanks for your patch.\n\nOn 2019-11-27 10:49:07 +0200, Laurent Pinchart wrote:\n> The Object class stores the number of pending messages that have been\n> posted for it, while the actual messages are stored in a per-thread list\n> in the ThreadData class. When dispatching messages, the message is\n> removed from the list, passed to the receiver, and the number of pending\n> messages is updated.\n> \n> In order to avoid too much contention on the list lock, the lock is\n> dropped to pass the message to the receiver and then taken again. This\n> creates a race condition window with Thread::removeMessages(), as the\n> number of pending messages for a receiver is briefly out of sync with\n> the pending messages list. The assertion at the end of removeMessages()\n> thus sometimes fails.\n> \n> Fix this by decrementing the pending messages counter before releasing\n> the lock in Thread::dispatchMessages(). This fixes the slow message\n> receiver test in MessageTest.\n> \n> Fixes: 01b930964acd (\"libcamera: thread: Add a messaging passing API\")\n> Signed-off-by: Laurent Pinchart \n\nReviewed-by: Niklas Söderlund \n\n> ---\n> src/libcamera/thread.cpp | 4 ++--\n> 1 file changed, 2 insertions(+), 2 deletions(-)\n> \n> diff --git a/src/libcamera/thread.cpp b/src/libcamera/thread.cpp\n> index 029a0e8fddd5..18ebd16a7e2f 100644\n> --- a/src/libcamera/thread.cpp\n> +++ b/src/libcamera/thread.cpp\n> @@ -439,11 +439,11 @@ void Thread::dispatchMessages()\n> \t\tObject *receiver = msg->receiver_;\n> \t\tASSERT(data_ == receiver->thread()->data_);\n> \n> +\t\treceiver->pendingMessages_--;\n> +\n> \t\tlocker.unlock();\n> \t\treceiver->message(msg.get());\n> \t\tlocker.lock();\n> -\n> -\t\treceiver->pendingMessages_--;\n> \t}\n> }\n> \n> -- \n> Regards,\n> \n> Laurent Pinchart\n> \n> _______________________________________________\n> libcamera-devel mailing list\n> libcamera-devel@lists.libcamera.org\n> https://lists.libcamera.org/listinfo/libcamera-devel","headers":{"Return-Path":"","Received":["from mail-lf1-x144.google.com (mail-lf1-x144.google.com\n\t[IPv6:2a00:1450:4864:20::144])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id 431F960C33\n\tfor ;\n\tWed, 27 Nov 2019 16:08:47 +0100 (CET)","by mail-lf1-x144.google.com with SMTP id l14so17429735lfh.10\n\tfor ;\n\tWed, 27 Nov 2019 07:08:47 -0800 (PST)","from localhost (h-93-159.A463.priv.bahnhof.se. 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