drm/msm/rd: Fix FIFO-full deadlock

[ Upstream commit 174974d8463b77c2b4065e98513adb204e64de7d ]

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@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/496706/
Link: https://lore.kernel.org/r/20220807160901.2353471-2-robdclark@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/msm/msm_rd.c b/drivers/gpu/drm/msm/msm_rd.c
index b55398a34fa481db54084a220c2da20d6a8df6dd..e3f0dd4a36792f5e35d4bce7e310edb7b685c598 100644 (file)
--- a/drivers/gpu/drm/msm/msm_rd.c
+++ b/drivers/gpu/drm/msm/msm_rd.c
@@ -191,6 +191,9 @@ 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.
         */