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Mon, 17 Aug 2026 05:43:06 -0700 (PDT) Received: from [127.0.0.1] ([2a09:bac6:3861:1e5a::306:a]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c217feb99d4sm52626266b.22.2026.08.17.05.43.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); 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 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 X-Rspamd-Queue-Id: 88373140003 X-Stat-Signature: 3e3z85zynjpf3hjhpqwwrgkho53rbi56 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1786970587-16194 X-HE-Meta: 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 NI22sHrA 1A7lyjPe+3uaij4GZZ85h8GEBoG2JUFjixXeIOctLGB6uDOAko99VowvE2PMSfn0av/NsQWQNalBNDAzCs7rj9RVXVuzTH+jZ7OK12IFTYCyqztLudZ8FW4aPa/zg0Q7SIiJXRAgzGb1SbxltjlwGnIb0+pcGlP2bqZvAO7l7GxLeVCQY1uh69Vwz6oe7iKBchlE+HxpRpgrGosHGqTdsDRnNwkRisVTZAe2w5iigoGSOxTaIFhF8scoroMbFrzQ3BrRB6+SbiPiDqdBMbqOIkgN6qCzrpqrghj/UjEGRtVxbmnc/AY1/qLr4Ovor0e6r5mi2vMHjFfEdpJ4DVfOBx3EehmJdTX4DpElH5AnTTRMSUrTW8/wnL0p3uwpaqHGb0wGzaThp8AQZHDQLB60yyWpYxA4NezBDPi6J+Wb7snzSklfcFjQWCMQNsoBOpRvkNlcWgQUX5F319BNMh2MAZ0S2KUBYwd2yVVzd Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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)