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Mon, 17 Aug 2026 05:43:05 -0700 (PDT) From: Caleb Kan Date: Mon, 17 Aug 2026 13:42:47 +0100 Subject: [PATCH RFC 7/9] drm/locking: preserve deadlock diagnostics for trie-backed stacks Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260817-stackdepot-trie-v1-7-53870ca1651b@cloudflare.com> References: <20260817-stackdepot-trie-v1-0-53870ca1651b@cloudflare.com> In-Reply-To: <20260817-stackdepot-trie-v1-0-53870ca1651b@cloudflare.com> To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, Vlastimil Babka , Alexander Potapenko , Marco Elver , Dmitry Vyukov , Andrey Konovalov , Oscar Salvador , Caleb Kan , kernel-team@cloudflare.com X-Mailer: b4 0.16.0 From: Caleb Kan 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(). Persistent stack depot saves can now return trie-backed handles, while stack_depot_fetch() remains limited to hash-backed records. Use stack_depot_snprint() to format either backend. Preserve the PAGE_SIZE buffer, two-space indentation, warning, and backtrace. Signed-off-by: Caleb Kan --- 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 2c806b0146d6..a2ddb02b2aea 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); -- Git-155)