drm/amdgpu: fix strsep() corrupting lockup_timeout on multi-GPU (v3)

amdgpu_device_get_job_timeout_settings() passes a pointer directly
to the global amdgpu_lockup_timeout[] buffer into strsep().
strsep() destructively replaces delimiter characters with '\0'
in-place.

On multi-GPU systems, this function is called once per device.
When a multi-value setting like "0,0,0,-1" is used, the first
GPU's call transforms the global buffer into "0\00\00\0-1". The
second GPU then sees only "0" (terminated at the first '\0'),
parses a single value, hits the single-value fallthrough
(index == 1), and applies timeout=0 to all rings — causing
immediate false job timeouts.

Fix this by copying into a stack-local array before calling
strsep(), so the global module parameter buffer remains intact
across calls. The buffer is AMDGPU_MAX_TIMEOUT_PARAM_LENGTH
(256) bytes, which is safe for the stack.

v2: wrap commit message to 72 columns, add Assisted-by tag.
v3: use stack array with strscpy() instead of kstrdup()/kfree()
    to avoid unnecessary heap allocation (Christian).

This patch was developed with assistance from Claude (claude-opus-4-6).

Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Ruijing Dong <ruijing.dong@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 94d79f5)
Cc: stable@vger.kernel.org

Author: ruijingdong

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -4207,7 +4207,8 @@ static void amdgpu_device_xgmi_reset_func(struct work_struct *__work)
 
 static int amdgpu_device_get_job_timeout_settings(struct amdgpu_device *adev)
 {
-	char *input = amdgpu_lockup_timeout;
+	char buf[AMDGPU_MAX_TIMEOUT_PARAM_LENGTH];
+	char *input = buf;
 	char *timeout_setting = NULL;
 	int index = 0;
 	long timeout;
@@ -4217,9 +4218,17 @@ static int amdgpu_device_get_job_timeout_settings(struct amdgpu_device *adev)
 	adev->gfx_timeout = adev->compute_timeout = adev->sdma_timeout =
 		adev->video_timeout = msecs_to_jiffies(2000);
 
-	if (!strnlen(input, AMDGPU_MAX_TIMEOUT_PARAM_LENGTH))
+	if (!strnlen(amdgpu_lockup_timeout, AMDGPU_MAX_TIMEOUT_PARAM_LENGTH))
 		return 0;
 
+	/*
+	 * strsep() destructively modifies its input by replacing delimiters
+	 * with '\0'. Use a stack copy so the global module parameter buffer
+	 * remains intact for multi-GPU systems where this function is called
+	 * once per device.
+	 */
+	strscpy(buf, amdgpu_lockup_timeout, sizeof(buf));
+
 	while ((timeout_setting = strsep(&input, ",")) &&
 	       strnlen(timeout_setting, AMDGPU_MAX_TIMEOUT_PARAM_LENGTH)) {
 		ret = kstrtol(timeout_setting, 0, &timeout);