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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Dmitry Osipenko <digetx@gmail.com>,
        Thierry Reding <treding@nvidia.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 080/270] gpu: host1x: debug: Fix multiple channels emitting messages simultaneously
Date:   Mon, 17 Aug 2020 17:14:41 +0200
Message-Id: <20200817143759.752045633@linuxfoundation.org>
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From: Dmitry Osipenko <digetx@gmail.com>

[ Upstream commit 35681862808472a0a4b9a8817ae2789c0b5b3edc ]

Once channel's job is hung, it dumps the channel's state into KMSG before
tearing down the offending job. If multiple channels hang at once, then
they dump messages simultaneously, making the debug info unreadable, and
thus, useless. This patch adds mutex which allows only one channel to emit
debug messages at a time.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/host1x/debug.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/host1x/debug.c b/drivers/gpu/host1x/debug.c
index c0392672a8421..1b4997bda1c79 100644
--- a/drivers/gpu/host1x/debug.c
+++ b/drivers/gpu/host1x/debug.c
@@ -16,6 +16,8 @@
 #include "debug.h"
 #include "channel.h"
 
+static DEFINE_MUTEX(debug_lock);
+
 unsigned int host1x_debug_trace_cmdbuf;
 
 static pid_t host1x_debug_force_timeout_pid;
@@ -52,12 +54,14 @@ static int show_channel(struct host1x_channel *ch, void *data, bool show_fifo)
 	struct output *o = data;
 
 	mutex_lock(&ch->cdma.lock);
+	mutex_lock(&debug_lock);
 
 	if (show_fifo)
 		host1x_hw_show_channel_fifo(m, ch, o);
 
 	host1x_hw_show_channel_cdma(m, ch, o);
 
+	mutex_unlock(&debug_lock);
 	mutex_unlock(&ch->cdma.lock);
 
 	return 0;
-- 
2.25.1