{"id":24102,"url":"https://patchwork.libcamera.org/api/1.1/patches/24102/?format=json","web_url":"https://patchwork.libcamera.org/patch/24102/","project":{"id":1,"url":"https://patchwork.libcamera.org/api/1.1/projects/1/?format=json","name":"libcamera","link_name":"libcamera","list_id":"libcamera_core","list_email":"libcamera-devel@lists.libcamera.org","web_url":"","scm_url":"","webscm_url":""},"msgid":"<20250814093138.2075098-1-barnabas.pocze@ideasonboard.com>","date":"2025-08-14T09:31:38","name":"[v1] libcamera: base: semaphore: Do not unlock prematurely","commit_ref":null,"pull_url":null,"state":"accepted","archived":false,"hash":"48b3a70f3925c3f062f2e87f692a6197518387b1","submitter":{"id":216,"url":"https://patchwork.libcamera.org/api/1.1/people/216/?format=json","name":"Barnabás Pőcze","email":"barnabas.pocze@ideasonboard.com"},"delegate":null,"mbox":"https://patchwork.libcamera.org/patch/24102/mbox/","series":[{"id":5374,"url":"https://patchwork.libcamera.org/api/1.1/series/5374/?format=json","web_url":"https://patchwork.libcamera.org/project/libcamera/list/?series=5374","date":"2025-08-14T09:31:38","name":"[v1] libcamera: base: semaphore: Do not unlock prematurely","version":1,"mbox":"https://patchwork.libcamera.org/series/5374/mbox/"}],"comments":"https://patchwork.libcamera.org/api/patches/24102/comments/","check":"pending","checks":"https://patchwork.libcamera.org/api/patches/24102/checks/","tags":{},"headers":{"Return-Path":"","X-Original-To":"parsemail@patchwork.libcamera.org","Delivered-To":"parsemail@patchwork.libcamera.org","Received":["from lancelot.ideasonboard.com (lancelot.ideasonboard.com\n\t[92.243.16.209])\n\tby patchwork.libcamera.org (Postfix) with ESMTPS id 5FFA7BDCC1\n\tfor ;\n\tThu, 14 Aug 2025 09:31:44 +0000 (UTC)","from lancelot.ideasonboard.com (localhost [IPv6:::1])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTP id 0B8196924F;\n\tThu, 14 Aug 2025 11:31:43 +0200 (CEST)","from perceval.ideasonboard.com (perceval.ideasonboard.com\n\t[213.167.242.64])\n\tby lancelot.ideasonboard.com (Postfix) with ESMTPS id E219861436\n\tfor ;\n\tThu, 14 Aug 2025 11:31:41 +0200 (CEST)","from pb-laptop.local (185.221.141.188.nat.pool.zt.hu\n\t[185.221.141.188])\n\tby perceval.ideasonboard.com (Postfix) with ESMTPSA id A335B83D\n\tfor ;\n\tThu, 14 Aug 2025 11:30:47 +0200 (CEST)"],"Authentication-Results":"lancelot.ideasonboard.com; dkim=pass (1024-bit key;\n\tunprotected) header.d=ideasonboard.com header.i=@ideasonboard.com\n\theader.b=\"S/FOyU83\"; dkim-atps=neutral","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com;\n\ts=mail; t=1755163847;\n\tbh=I0/DirPIgO38PUMSqdQ03zf+CJIFSEKX1wvPLrmXlgw=;\n\th=From:To:Subject:Date:From;\n\tb=S/FOyU83ocvAjLlKbRYKmuY5nMRpXZFpEhxp8SmOOTcqg+949P6a8T84RoSbyJ8AF\n\tVgvpZnVIlQ87PyQQs3fQgtIOBdnU0pzMBwp8G3RGej7yH+bGYYE7xjcUsQK4PBL/07\n\tBSzrE833WCP2DiSuPPao3FkSckKgDLALqe4uXhzM=","From":"=?utf-8?q?Barnab=C3=A1s_P=C5=91cze?= ","To":"libcamera-devel@lists.libcamera.org","Subject":"[PATCH v1] libcamera: base: semaphore: Do not unlock prematurely","Date":"Thu, 14 Aug 2025 11:31:38 +0200","Message-ID":"<20250814093138.2075098-1-barnabas.pocze@ideasonboard.com>","X-Mailer":"git-send-email 2.50.1","MIME-Version":"1.0","Content-Type":"text/plain; charset=UTF-8","Content-Transfer-Encoding":"8bit","X-BeenThere":"libcamera-devel@lists.libcamera.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"","List-Unsubscribe":",\n\t","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n\t","Errors-To":"libcamera-devel-bounces@lists.libcamera.org","Sender":"\"libcamera-devel\" "},"content":"In `Semaphore::release()`, unlocking the mutex before signalling the condition\nvariable can be problematic, especially with \"temporary\" objects such as the\nones `BoundMethodBase::activatePack()` uses to handle `ConnectionTypeBlocking`.\n\nSpecifically, `Semaphore::acquire()` might lock the mutex after `Semaphore::release()`\nhas unlocked it, but before it had the chance to notify the condition variable.\nIn that case `Semaphore::acquire()` can succeed, and execution may proceed to\ndestroy the `Semaphore` object while the other thread is in the process of\nrunning `std::condition_variable::notify_all()`.\n\nSee [0] for essentially the same issue in libcxx and its fix at [1].\n\n[0]: https://github.com/llvm/llvm-project/issues/23667\n[1]: https://github.com/llvm/llvm-project/commit/b3ec43d78aa2599e1592392844a7ec638fab7902\n\nBug: https://bugs.libcamera.org/show_bug.cgi?id=225\nSigned-off-by: Barnabás Pőcze \n---\n src/libcamera/base/semaphore.cpp | 6 ++----\n 1 file changed, 2 insertions(+), 4 deletions(-)","diff":"diff --git a/src/libcamera/base/semaphore.cpp b/src/libcamera/base/semaphore.cpp\nindex 862f3b313..6aec8b92d 100644\n--- a/src/libcamera/base/semaphore.cpp\n+++ b/src/libcamera/base/semaphore.cpp\n@@ -93,11 +93,9 @@ bool Semaphore::tryAcquire(unsigned int n)\n */\n void Semaphore::release(unsigned int n)\n {\n-\t{\n-\t\tMutexLocker locker(mutex_);\n-\t\tavailable_ += n;\n-\t}\n+\tMutexLocker locker(mutex_);\n \n+\tavailable_ += n;\n \tcv_.notify_all();\n }\n \n","prefixes":["v1"]}