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Tue, 08 Sep 2026 06:13:59 -0700 (PDT) Received: from [127.0.0.1] ([2a09:bac6:37a9:1e5a::306:1]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c260d6e1c93sm625170866b.63.2026.09.08.06.13.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Sep 2026 06:13:59 -0700 (PDT) From: Caleb Kan Date: Tue, 08 Sep 2026 14:13:40 +0100 Subject: [PATCH RFC v2 07/11] 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: <20260908-stackdepot-trie-v2-7-1996d5cef732@cloudflare.com> References: <20260908-stackdepot-trie-v2-0-1996d5cef732@cloudflare.com> In-Reply-To: <20260908-stackdepot-trie-v2-0-1996d5cef732@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-Server: rspam05 X-Rspamd-Queue-Id: 1EB8140008 X-Stat-Signature: jerprehzzqsrszatjicehcrjig3hs6wk X-Rspam-User: X-HE-Tag: 1788873240-176286 X-HE-Meta: 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 +jENbf51 xLY2ALBCOk3RC4L6gQAFAUk9dGVB+Ft2hng9pceO0bHCJ6E3VlK94m5E8jkxkllEijrhtcZztU8n3NPTHmTmI63ZKYxjkqWd61fYuXCKpq/5oh5e6m8aJKHv3Uf3+HuYZaG33Ed97N6zWm8HrCnP8yt/N0zC/p/0q6QH1sIVYGQGCjILaihvm6XCk7V6fSmCFRoNWjizDYWPMwpmZVmdtPnqFih76c5CMCQrryJPGTe+iu9OHJ3NxIzxF1j5ziZJFIYxaOKqj18Q8LK2ytO9Nk3ReKe0452zjA9cB5gcqtIWfKviYsemYSu4yUL4IQMNP1aDSLit9JI5+6Qpe1MwGnLEFtsIWRkhhtN9p/J+dVav4fU1rahZ7J83v+T+z1tAFTAVJSj2GhUWC09nxJcypcXeCzgKo0UFIKgtKT3L6OmUSkdyPBbWShZoWylnjycTmv/0sEeVjYfXVwU4lcKvhShe4b6pEw3QqyZCd 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(). A later patch allows persistent stack depot saves to return trie-backed handles, while stack_depot_fetch() remains limited to hash-backed records. Use stack_depot_snprint() to format either backend. Keep the PAGE_SIZE buffer and leave the warning text, existing indentation, and backtrace unchanged. 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 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); -- Git-155)