linux-kernel - [PATCH v2 2/2] drm/msm/rd: Fix FIFO-full deadlock

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Message-Id: <20220807160901.2353471-2-robdclark@gmail.com>
Date:   Sun,  7 Aug 2022 09:09:01 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v2 2/2] drm/msm/rd: Fix FIFO-full deadlock

From: Rob Clark <robdclark@...omium.org>

If the previous thing cat'ing $debugfs/rd left the FIFO full, then
subsequent open could deadlock in rd_write() (because open is blocked,
not giving a chance for read() to consume any data in the FIFO).  Also
it is generally a good idea to clear out old data from the FIFO.

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/msm/msm_rd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/msm/msm_rd.c b/drivers/gpu/drm/msm/msm_rd.c
index a92ffde53f0b..db2f847c8535 100644
--- a/drivers/gpu/drm/msm/msm_rd.c
+++ b/drivers/gpu/drm/msm/msm_rd.c
@@ -196,6 +196,9 @@ static int rd_open(struct inode *inode, struct file *file)
 	file->private_data = rd;
 	rd->open = true;
 
+	/* Reset fifo to clear any previously unread data: */
+	rd->fifo.head = rd->fifo.tail = 0;
+
 	/* the parsing tools need to know gpu-id to know which
 	 * register database to load.
 	 *
-- 
2.36.1