[PATCH v3 05/10] drm/locking: print deadlock backtraces with stack_depot_snprint()

[Matt Fleming <matt@readmodwrite.com>]

From: Caleb Kan <ckan@cloudflare.com>

When a modeset lock acquisition returns -EDEADLK, DRM saves the call chain
and prints it if the caller later attempts another lock or drops its locks
without first calling drm_modeset_backoff(). This diagnostic currently
fetches the saved stack through stack_depot_fetch().

Later patches compress the frames of persistent stack depot records and
remove stack_depot_fetch(), which cannot return a pointer to them.
Use stack_depot_snprint() to format the stack. Keep the PAGE_SIZE
buffer and leave the warning text, existing indentation, and backtrace
unchanged.

Signed-off-by: Caleb Kan <ckan@cloudflare.com>
[mfleming: reworded for compressed frames]
Signed-off-by: Matt Fleming <mfleming@cloudflare.com>
---
 drivers/gpu/drm/drm_modeset_lock.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index e14814c30d8c..f48b02379b71 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -94,16 +94,13 @@ static noinline depot_stack_handle_t __drm_stack_depot_save(void)
 static void __drm_stack_depot_print(depot_stack_handle_t stack_depot)
 {
 	struct drm_printer p = drm_dbg_printer(NULL, DRM_UT_KMS, "drm_modeset_lock");
-	unsigned long *entries;
-	unsigned int nr_entries;
 	char *buf;
 
 	buf = kmalloc(PAGE_SIZE, GFP_NOWAIT | __GFP_NOWARN);
 	if (!buf)
 		return;
 
-	nr_entries = stack_depot_fetch(stack_depot, &entries);
-	stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 2);
+	stack_depot_snprint(stack_depot, buf, PAGE_SIZE, 2);
 
 	drm_printf(&p, "attempting to lock a contended lock without backoff:\n%s", buf);
 
-- 
2.43.0