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Thu, 13 Feb 2020 00:00:11 -0800 (PST) Date: Thu, 13 Feb 2020 15:59:57 +0800 Message-Id: <20200213153226.I477092c2f104fd589133436c3ae4590e6fc6323b@changeid> Mime-Version: 1.0 X-Mailer: git-send-email 2.25.0.225.g125e21ebc7-goog From: Tzung-Bi Shih To: broonie@kernel.org, airlied@linux.ie, daniel@ffwll.ch Cc: alsa-devel@alsa-project.org, cychiang@google.com, tzungbi@google.com, dri-devel@lists.freedesktop.org, ck.hu@mediatek.com, linux-mediatek@lists.infradead.org, p.zabel@pengutronix.de, matthias.bgg@gmail.com, dgreid@google.com, linux-arm-kernel@lists.infradead.org Subject: [alsa-devel] [PATCH] drm/mediatek: fix race condition for HDMI jack status reporting X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" hdmi_conn_detect and mtk_hdmi_audio_hook_plugged_cb would be called by different threads. Imaging the following calling sequence: Thread A Thread B -------------------------------------------------------------------- mtk_hdmi_audio_hook_plugged_cb() mtk_cec_hpd_high() -> disconnected hdmi_conn_detect() mtk_cec_hpd_high() -> connected plugged_cb(connected) plugged_cb(disconnected) The latest disconnected is false reported. Makes mtk_cec_hpd_high and plugged_cb atomic to fix. plugged_cb and codec_dev are also in danger of race condition. Instead of using mutex to protect them: - Checks NULLs first. - Uses WRITE_ONCE() to prevent store tearing (i.e. write to plugged_cb after codec_dev). - Uses codec_dev as a signal to report HDMI jack status. Fixes: 5d3c64477392 ("drm/mediatek: support HDMI jack status reporting") Signed-off-by: Tzung-Bi Shih --- Previous discussion: https://patchwork.kernel.org/patch/11367625/ Previous attempt: https://patchwork.kernel.org/patch/11378413/ drivers/gpu/drm/mediatek/mtk_hdmi.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediatek/mtk_hdmi.c index 03aeb73005ef..b1e5d0c538fa 100644 --- a/drivers/gpu/drm/mediatek/mtk_hdmi.c +++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -171,6 +172,7 @@ struct mtk_hdmi { bool enabled; hdmi_codec_plugged_cb plugged_cb; struct device *codec_dev; + struct mutex update_plugged_status_lock; }; static inline struct mtk_hdmi *hdmi_ctx_from_bridge(struct drm_bridge *b) @@ -1199,10 +1201,13 @@ static void mtk_hdmi_clk_disable_audio(struct mtk_hdmi *hdmi) static enum drm_connector_status mtk_hdmi_update_plugged_status(struct mtk_hdmi *hdmi) { - bool connected = mtk_cec_hpd_high(hdmi->cec_dev); + bool connected; - if (hdmi->plugged_cb && hdmi->codec_dev) + mutex_lock(&hdmi->update_plugged_status_lock); + connected = mtk_cec_hpd_high(hdmi->cec_dev); + if (hdmi->codec_dev) hdmi->plugged_cb(hdmi->codec_dev, connected); + mutex_unlock(&hdmi->update_plugged_status_lock); return connected ? connector_status_connected : connector_status_disconnected; @@ -1669,8 +1674,12 @@ static int mtk_hdmi_audio_hook_plugged_cb(struct device *dev, void *data, { struct mtk_hdmi *hdmi = data; - hdmi->plugged_cb = fn; - hdmi->codec_dev = codec_dev; + if (!fn || !codec_dev) + return -EINVAL; + + /* Use WRITE_ONCE() to prevent store tearing. */ + WRITE_ONCE(hdmi->plugged_cb, fn); + WRITE_ONCE(hdmi->codec_dev, codec_dev); mtk_hdmi_update_plugged_status(hdmi); return 0; @@ -1729,6 +1738,7 @@ static int mtk_drm_hdmi_probe(struct platform_device *pdev) return ret; } + mutex_init(&hdmi->update_plugged_status_lock); platform_set_drvdata(pdev, hdmi); ret = mtk_hdmi_output_init(hdmi);