From patchwork Thu Jun 30 00:02:51 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Laurent Pinchart X-Patchwork-Id: 16449 Return-Path: X-Original-To: parsemail@patchwork.libcamera.org Delivered-To: parsemail@patchwork.libcamera.org Received: from lancelot.ideasonboard.com (lancelot.ideasonboard.com [92.243.16.209]) by patchwork.libcamera.org (Postfix) with ESMTPS id 3BDBCBD808 for ; Thu, 30 Jun 2022 00:03:37 +0000 (UTC) Received: from lancelot.ideasonboard.com (localhost [IPv6:::1]) by lancelot.ideasonboard.com (Postfix) with ESMTP id CFB6F6564F; Thu, 30 Jun 2022 02:03:36 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=libcamera.org; s=mail; t=1656547416; bh=qBGpVUVKbXxHaRDq7EPNyffLvbZ/SABnSN8OUzibW2g=; h=To:Date:In-Reply-To:References:Subject:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=4ZTT3bD0mg+m0Uej1D+VZjByPUFEdeMf6nMicwRMb+ss4HWDQCyCDtsb3H18sPN/e wSRYicLsG2uwxkRxs3m6X/jgXxDurq4dvzBRt5nHpLN99xQYfuPbkGa8TrTsqi3eRe gvvCCOozpHSiihnZldc/Gsfk8BkpVwvpc5OGua8kcmtbIaLQJELYBXFAzqSDcbWoff UpEgYWDtntgxhTe3uSlzEFAUeLhCOtLWtLnGqdnLixRV/RLRbESaVHTOl2IqqEpWWT StsC23lCSXIVaUQoo1hmPgFZN0sz+387bg5PslGsGxgpKwsAtG2zfcujPAdgtBKLtT 1hUJOVGzCbTVA== Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lancelot.ideasonboard.com (Postfix) with ESMTPS id 8BD5A65646 for ; Thu, 30 Jun 2022 02:03:20 +0200 (CEST) Authentication-Results: lancelot.ideasonboard.com; dkim=pass (1024-bit key; unprotected) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="Hgnb9YsY"; dkim-atps=neutral Received: from pendragon.lan (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 20E6159D; Thu, 30 Jun 2022 02:03:20 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1656547400; bh=qBGpVUVKbXxHaRDq7EPNyffLvbZ/SABnSN8OUzibW2g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Hgnb9YsYoOQgLsnulTtOtlRNsOjXafVFj24JUv0WAFaquFNLpuZYGAkpxF17dsGk7 iq46oPFuXAtb9nJzMMRfnOdl/OnLNY8bnQAJ6eUCD8OsWQoVYYjybVhHxTK6Ozbq5U tUqcsavYtGVwkcjfM1g0X1UPLJqSHD42+LCcyiUA= To: libcamera-devel@lists.libcamera.org Date: Thu, 30 Jun 2022 03:02:51 +0300 Message-Id: <20220630000251.31295-13-laurent.pinchart@ideasonboard.com> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220630000251.31295-1-laurent.pinchart@ideasonboard.com> References: <20220630000251.31295-1-laurent.pinchart@ideasonboard.com> MIME-Version: 1.0 Subject: [libcamera-devel] [PATCH v2 12/12] gstreamer: Fix race conditions in task pause/resume X-BeenThere: libcamera-devel@lists.libcamera.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Laurent Pinchart via libcamera-devel From: Laurent Pinchart Reply-To: Laurent Pinchart Cc: Nicolas Dufresne Errors-To: libcamera-devel-bounces@lists.libcamera.org Sender: "libcamera-devel" The task run function races with two other threads that want to resume the task: the requestCompleted() handler and the buffer-notify signal handler. If the former queues completed requests or the latter queues back buffers to the pool, and then resume the task, after the task run handler checks the queues but before it attemps to pause the task, then the task may be paused without noticing that more work is available. The most immediate way to fix this is to take the stream_lock in the requestCompleted() and buffer-notify signal handlers, or cover the whole task run handler with the GstLibcameraSrcState lock. This could cause long delays in the requestCompleted() handler, so that's not a good option. Instead, add a wakeup flag, preotected by the GstLibcameraSrcState lock, that allows detection of a lost race, and retry the task run. Signed-off-by: Laurent Pinchart --- Changes since v1: - Fix incorrect wakeup and pause logic --- src/gstreamer/gstlibcamerasrc.cpp | 84 +++++++++++++++++++++++-------- 1 file changed, 63 insertions(+), 21 deletions(-) diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp index 9ea59631a9f2..5471ab951252 100644 --- a/src/gstreamer/gstlibcamerasrc.cpp +++ b/src/gstreamer/gstlibcamerasrc.cpp @@ -118,7 +118,7 @@ struct GstLibcameraSrcState { /* * Contention on this lock_ must be minimized, as it has to be taken in * the realtime-sensitive requestCompleted() handler to protect - * queuedRequests_ and completedRequests_. + * queuedRequests_, completedRequests_ and wakeup_. * * stream_lock must be taken before lock_ in contexts where both locks * need to be taken. In particular, this means that the lock_ must not @@ -130,6 +130,7 @@ struct GstLibcameraSrcState { LIBCAMERA_TSA_GUARDED_BY(lock_); std::queue> completedRequests_ LIBCAMERA_TSA_GUARDED_BY(lock_); + bool wakeup_ LIBCAMERA_TSA_GUARDED_BY(lock_); guint group_id_; @@ -250,15 +251,17 @@ GstLibcameraSrcState::requestCompleted(Request *request) { MutexLocker locker(lock_); completedRequests_.push(std::move(wrap)); - } + wakeup_ = true; - gst_task_resume(src_->task); + gst_task_resume(src_->task); + } } /* Must be called with stream_lock held. */ int GstLibcameraSrcState::processRequest() { std::unique_ptr wrap; + int err = 0; { MutexLocker locker(lock_); @@ -267,10 +270,13 @@ int GstLibcameraSrcState::processRequest() wrap = std::move(completedRequests_.front()); completedRequests_.pop(); } + + if (completedRequests_.empty()) + err = -ENOBUFS; } if (!wrap) - return -ENODATA; + return -ENOBUFS; GstFlowReturn ret = GST_FLOW_OK; gst_flow_combiner_reset(src_->flow_combiner); @@ -310,7 +316,7 @@ int GstLibcameraSrcState::processRequest() return -EPIPE; } - return 0; + return err; } static bool @@ -374,53 +380,88 @@ gst_libcamera_src_open(GstLibcameraSrc *self) return true; } +static void +gst_libcamera_src_task_resume(gpointer user_data) +{ + GstLibcameraSrc *self = GST_LIBCAMERA_SRC(user_data); + GstLibcameraSrcState *state = self->state; + + MutexLocker locker(state->lock_); + state->wakeup_ = true; + gst_task_resume(self->task); +} + static void gst_libcamera_src_task_run(gpointer user_data) { GstLibcameraSrc *self = GST_LIBCAMERA_SRC(user_data); GstLibcameraSrcState *state = self->state; + { + MutexLocker locker(state->lock_); + state->wakeup_ = false; + } + + bool doPause = true; + /* * Create and queue one request. If no buffers are available the * function returns -ENOBUFS, which we ignore here as that's not a * fatal error. */ int ret = state->queueRequest(); - if (ret == -ENOMEM) { + switch (ret) { + case 0: + /* + * The request was successfully queued, there may be enough + * buffers to create a new one. Don't pause the task to give it + * another try. + */ + doPause = false; + break; + + case -ENOMEM: GST_ELEMENT_ERROR(self, RESOURCE, NO_SPACE_LEFT, ("Failed to allocate request for camera '%s'.", state->cam_->id().c_str()), ("libcamera::Camera::createRequest() failed")); gst_task_stop(self->task); return; + + case -ENOBUFS: + default: + break; } - /* Process one completed request, if available. */ + /* + * Process one completed request, if available, and record if further + * requests are ready for processing. + */ ret = state->processRequest(); switch (ret) { + case -ENOBUFS: + doPause = false; + break; + case -EPIPE: gst_task_stop(self->task); return; - case -ENODATA: - gst_task_pause(self->task); - return; + case 0: + default: + break; } /* - * Here we need to decide if we want to pause. This needs to - * happen in lock step with the callback thread which may want - * to resume the task and might push pending buffers. + * Here we need to decide if we want to pause. This needs to happen in + * lock step with the requestCompleted callback and the buffer-notify + * signal handler that resume the task. */ - bool do_pause; - - { + if (doPause) { MutexLocker locker(state->lock_); - do_pause = state->completedRequests_.empty(); + if (!state->wakeup_) + gst_task_pause(self->task); } - - if (do_pause) - gst_task_pause(self->task); } static void @@ -531,7 +572,8 @@ gst_libcamera_src_task_enter(GstTask *task, [[maybe_unused]] GThread *thread, GstLibcameraPool *pool = gst_libcamera_pool_new(self->allocator, stream_cfg.stream()); g_signal_connect_swapped(pool, "buffer-notify", - G_CALLBACK(gst_task_resume), task); + G_CALLBACK(gst_libcamera_src_task_resume), + self); gst_libcamera_pad_set_pool(srcpad, pool); gst_flow_combiner_add_pad(self->flow_combiner, srcpad);