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Fri, 19 Sep 2025 01:59:02 -0700 (PDT) From: Menglong Dong To: Masami Hiramatsu Cc: peterz@infradead.org, jolsa@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, kees@kernel.org, samitolvanen@google.com, rppt@kernel.org, luto@kernel.org, mhiramat@kernel.org, ast@kernel.org, andrii@kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH] x86/ibt: make is_endbr() notrace Date: Fri, 19 Sep 2025 16:58:57 +0800 Message-ID: <5925436.DvuYhMxLoT@7940hx> In-Reply-To: <20250919175255.f7c2c77fa03665a42b148046@kernel.org> References: <20250918120939.1706585-1-dongml2@chinatelecom.cn> <20250919175255.f7c2c77fa03665a42b148046@kernel.org> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" On 2025/9/19 16:52 Masami Hiramatsu write: > On Thu, 18 Sep 2025 20:09:39 +0800 > Menglong Dong wrote: > > > is_endbr() is called in __ftrace_return_to_handler -> fprobe_return -> > > kprobe_multi_link_exit_handler -> is_endbr. > > > > It is not protected by the "bpf_prog_active", so it can't be traced by > > kprobe-multi, which can cause recurring and panic the kernel. Fix it by > > make it notrace. > > Ah, OK. This is fprobe's issue. fprobe depends on fgraph to check > recursion, but fgraph only detects the recursion in the entry handler. > Thus it happens in the exit handler, fprobe does not check the recursion. > > But since the fprobe provides users to register callback at exit, it > should check the recursion in return path too. That's a good idea to provide recursion checking for the exit handler, which is able to solve this problem too. If so, we don't need to check the recursion on the kprobe-multi anymore. Do we? Thanks! Menglong Dong > > Thanks, > > -- > Masami Hiramatsu (Google) >