linux-kernel - [PATCH AUTOSEL 6.14 441/642] drm/xe/debugfs: fixed the return value of wedged_mode

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Message-Id: <20250505221419.2672473-441-sashal@kernel.org>
Date: Mon,  5 May 2025 18:10:57 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Xin Wang <x.wang@...el.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Fei Yang <fei.yang@...el.com>,
	Shuicheng Lin <shuicheng.lin@...el.com>,
	Sasha Levin <sashal@...nel.org>,
	lucas.demarchi@...el.com,
	thomas.hellstrom@...ux.intel.com,
	airlied@...il.com,
	simona@...ll.ch,
	intel-xe@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 6.14 441/642] drm/xe/debugfs: fixed the return value of wedged_mode_set

From: Xin Wang <x.wang@...el.com>

[ Upstream commit 6884d2051011f4db9e2f0b85709c79a8ced13bd6 ]

It is generally expected that the write() function should return a
positive value indicating the number of bytes written or a negative
error code if an error occurs. Returning 0 is unusual and can lead
to unexpected behavior.

When the user program writes the same value to wedged_mode twice in
a row, a lockup will occur, because the value expected to be
returned by the write() function inside the program should be equal
to the actual written value instead of 0.

To reproduce the issue:
echo 1 > /sys/kernel/debug/dri/0/wedged_mode
echo 1 > /sys/kernel/debug/dri/0/wedged_mode   <- lockup here

Signed-off-by: Xin Wang <x.wang@...el.com>
Cc: Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc: Fei Yang <fei.yang@...el.com>
Cc: Shuicheng Lin <shuicheng.lin@...el.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@...el.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250213223615.2327367-1-x.wang@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@...el.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/xe/xe_debugfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_debugfs.c b/drivers/gpu/drm/xe/xe_debugfs.c
index 492b4877433f1..6bfdd3a9913fd 100644
--- a/drivers/gpu/drm/xe/xe_debugfs.c
+++ b/drivers/gpu/drm/xe/xe_debugfs.c
@@ -166,7 +166,7 @@ static ssize_t wedged_mode_set(struct file *f, const char __user *ubuf,
 		return -EINVAL;
 
 	if (xe->wedged.mode == wedged_mode)
-		return 0;
+		return size;
 
 	xe->wedged.mode = wedged_mode;
 
-- 
2.39.5