From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=216.40.44.15 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793640855; b=VL/YN2YrHTi/fma+DEtvjyQZ7a3mfXG2BPRjtmxec2cIaMNsny0vc0d8kyfe2qhGgli2 1tEAFCwqePxpnSwFmWRyhfdu8VWOV0S9hq5ar67utUIcH6/9ELOd83QqET/wtel4tmVGT 56TIwuJWPsTbjVr6YLRHPfCTX/zYHYztNYfjznezdgwmkFr9QRzVt35HUXY7jGj2npKo8 jC7zCCtYQG0I4ALwQykreMWIWTOi74Y5Pz6AXV7vt0+oxexXYtRe8ujsyFvNgObMaH6g7 EgM5kAARzDbgFGQtZU4yU/yVtqy8sU5HpUjNnyTlMKJsNIQGeEgNYAbHlrKloqawKJg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793640855; h=DMARC-Filter:Received:Received:Date:From:To:Cc:Subject:Message-ID: In-Reply-To:References:X-Mailer:MIME-Version:Content-Type: Content-Transfer-Encoding:X-Rspamd-Server:X-Rspamd-Queue-Id: X-Stat-Signature:X-Spam-Status:X-Session-Marker:X-Session-ID: DKIM-Signature:X-HE-Tag:X-HE-Meta; bh=qpq7lIG5/HRt+2swVzeYdkDxOzJtStedVh4a/jEaJD8=; b=r+UuV+ZhMj5cq9iq8ilybG35DgCOvRbr3w5HvM2vI9tFt/hVGGWv3demUNGm0aRIFqWe KKOFsR7z7iKSsghC2hLfr3Eoth+drl3fl6zj+jgIZ3iMb1HntT+9+3TVDqt9l5tMFgH67 b8zvikm1BelGWukH6GRRPmKZ0TNDwNobVecFsUpMaDFMOaIC+ylK0ZDVHc1MtIXKfkVuQ R+uVn6AZhBJSJehw1j9kk/MWDTSmHQxMA68oB1Z+h1rVKhzJjOzetlOuhuYSTNVsppXmO C9V2svxwpgAXkLZ3puG5iJ7V1wpETKc7u9R+jslIobNgyUQxLyQXnLY5b1q6u9KGaWQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; dkim=pass header.d=goodmis.org header.i=@goodmis.org header.a=rsa-sha256 header.s=dkim1 header.b=5KCmrODy; arc=none smtp.remote-ip=216.40.44.15 Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 468FB606C3FE; Mon, 2 Nov 2026 17:34:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 468FB606C3FE Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=goodmis.org header.i=@goodmis.org header.a=rsa-sha256 header.s=dkim1 header.b=5KCmrODy Received: from omf04.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id D48011C0B81; Mon, 2 Nov 2026 17:34:11 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf04.hostedemail.com (Postfix) with ESMTPA id 3FAA72002D; Mon, 2 Nov 2026 17:34:09 +0000 (UTC) Date: Mon, 2 Nov 2026 12:34:08 -0500 From: Steven Rostedt To: "Masami Hiramatsu (Google)" Cc: Jonathan Corbet , Naveen N Rao , "David S . Miller" , Mathieu Desnoyers , Shuah Khan , Randy Dunlap , Tiezhu Yang , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, John Ogness Subject: Re: [PATCH 0/3] probes: Use trace_printk() in probe handlers Message-ID: <20261102123408.0fb950bf@gandalf.local.home> In-Reply-To: <179360345418.115681.193455787480210412.stgit@devnote2> References: <179360345418.115681.193455787480210412.stgit@devnote2> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspamout03 X-Rspamd-Queue-Id: 3FAA72002D X-Stat-Signature: 7ckdacpycu7hbqk64obfj93p47cit5qh X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/guh2Tz/bFMPzEWGFSiw4+Tr0ihxK2MSI= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=qpq7lIG5/HRt+2swVzeYdkDxOzJtStedVh4a/jEaJD8=; b=5KCmrODyWfBoGvRe+QqlpeXT4OKDHJN4t1gtVIqx8xdkV5NbI6dAilJx6THR4qE1j6TUNYDbOGrFJP0WGwxxGx+5lzY2itfP6QSu8zhR9fC7FtQJR/b9p6iYzZRifBh2Babe05GQHXzDzROooiY7HCWc7pNeTvcx8rl99a/rjoI= X-HE-Tag: 1793640849-471523 X-HE-Meta: U2FsdGVkX1/cHMCQNDM9YHYra2VrVZpn3rMXZqoKFr9Um4okpo1JBddl+5jKSfjOfD/U3u1uTSMtWsIw4eIzu5a2PgP1iExl08tr+3AstoqZe5Abx/0FEXbrxyRBo0CgKe5QEu4ncFHJ9Z1wGTBzT6aFAEG/4xQ/1RR8fC1mnRelRlfiqk98d/eiRj71r5dMK+s4OPx+LmWDL9ItUrdit09lihy2DbuZWTsGvAIX3+AGIYr767O6K7EEJ6qnZIcZW9XsMjx9or50Q/d1nkfPHy9XJBmqBgk4gmgUwpOjx+RGbq/LuKvJN9/Raiwtlf5/0AkVI77Zl5Pe5HBkwmJpkB8q3B2t47kA [ Cc'ing John Ogness ] On Mon, 2 Nov 2026 16:10:54 +0900 "Masami Hiramatsu (Google)" wrote: > Hi, > > Here are patches to update the probe sample code to use trace_printk > instead of normal printk. Since the fprobe and kprobe/kretprobe handlers > can be called from somewhere where console is locked, using printk() is > basically unsafe. Only the unoptimized kprobe on x86 is safe because it > is ran with NMI context (in this case, the kernel uses printk_deferred() > automatically), but optimized kprobe/kretprobe/fprobe are not. I don't think printk() is unsafe in these situations anymore. John? -- Steve > > Thus, this series replaces those printk() (pr_*()) with trace_printk() > which should be safe to output the result into trace buffer, and use > trace_dump_stack() instead of stack_trace_print(). > > The similar issue had been reported by Tiezhu Yang [1] in 2023, but > it was pointed different reason, and not applicable to upstream. > I investigated it again. > > [1] https://lore.kernel.org/all/d179086d-78d8-d0e3-e113-9072cffa55f4@loongson.cn/ > > Thank you, > --- > base-commit: bc71431221f5ba8bb33918399552636e059c2c45 > > Masami Hiramatsu (Google) (3): > samples/kprobes: Use trace_printk() in probe handlers > samples/fprobe: Use trace_printk() and trace_dump_stack() > docs: trace: Warn against using printk() in probe handlers > > > Documentation/trace/fprobe.rst | 5 +++ > Documentation/trace/kprobes.rst | 11 +++++- > samples/Kconfig | 4 +- > samples/fprobe/fprobe_example.c | 49 +++++-------------------- > samples/kprobes/kprobe_example.c | 69 ++++++++++++++++++----------------- > samples/kprobes/kretprobe_example.c | 10 +++-- > 6 files changed, 66 insertions(+), 82 deletions(-) > > -- > Masami Hiramatsu (Google)