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Sat, 26 Sep 2026 01:29:13 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Sat, 26 Sep 2026 08:29:12 +0000 Message-Id: From: "Alexei Starovoitov" To: "Jay Wang" , , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" Cc: "Alan Maguire" , "Martin KaFai Lau" , "Yonghong Song" , "Jiri Olsa" , "Nathan Chancellor" , "Nicolas Schier" , , "Luis Chamberlain" , "Petr Pavlu" , "Sami Tolvanen" , , "Miguel Ojeda" , , "Arnd Bergmann" , , "Hazem Mohamed Abuelfotoh" , "Bjoern Doebel" , "Martin Pohlack" , Subject: Re: [PATCH bpf-next v3 4/9] bpf: take the vmlinux BTF from the btf_vmlinux module In-Reply-To: <20260925224229.1850-5-wanjay@amazon.com> References: <20260925224229.1850-1-wanjay@amazon.com> <20260925224229.1850-5-wanjay@amazon.com> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, Sep 25, 2026 at 10:42 PM Jay Wang wrote: > + if (!data && load) { > + /* > + * The module notifier installs the BTF before init_module() > + * returns, so it is either there after this or the module is > + * not available (yet). Not cached: a later call retries, > + * e.g. once the module becomes reachable on the root fs. > + */ > + request_module("btf_vmlinux"); This will deadlock. event_btf_ids_read() calls btf_get_module_btf(NULL) with event_mutex held. With =m and BTF not loaded yet cat /sys/kernel/tracing/events/sched/sched_switch/btf_ids gets here and waits for modprobe. modprobe gets to trace_module_notify() which takes event_mutex. lockdep doesn't see it. print_function_args() gets here for every line of the trace, from ftrace_dump() with irqs off too. When the module is not installed that is one modprobe per line. Every caller of bpf_get_btf_vmlinux() and bpf_find_btf_id() was written for a function that doesn't wait for user space. pw-bot: cr