From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2EB6531812C; Mon, 8 Dec 2025 07:19:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765178399; cv=none; b=rEjaSewWImqovGq0W8vHo0+YoXfwOUTKHCtgQf2m2jRjfZ+42Fqby+KdWn9iuFa2O4H886xa3Vjn8ctSwGK8jyfmf4jsh9l+aTu4SELxNrL3K/UiOViRwRr6WaBZygesV+nvaWus9cStHCapLfi2b4t2zxwakO97eMXTEja9cwA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765178399; c=relaxed/simple; bh=9o3BrEm1VDHGtDidlZHe7Kv4vviEVWPLkbywRUuELO0=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=gv55WNIQ0RkWTaZxioIX873wWI28zHPi/v13wkbOCT5KBHQEM7VPlycH2e7BSQqb7zWlbuynH7lJq9Gc3xh+sxdWoI9xo6qHkVDlw7IZTFMDNYO/sDfMMY4ENJdO/Xg2Gs59fDZroWei4EIVBkAABAU0n+sa0y9dCF/slr/g19c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bZydf0uL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bZydf0uL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65A7EC4CEF1; Mon, 8 Dec 2025 07:19:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765178398; bh=9o3BrEm1VDHGtDidlZHe7Kv4vviEVWPLkbywRUuELO0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=bZydf0uL5ye9BCcgPZpNQULCgDlGnb56NBnJxtCVttAGoka/21t9xOrRZ4dAW0N4K PSsOUbf5spsHV3t5td6ZtHZQOFcJ+ZWfvNvtL2T4xmRBbKue5vqNI2XvI+lZ6R+MJ5 bJUC56v18Z2fTHQ/qn4xrFmqbiWbRTFUmMkwDVt66Mi+0BSpai1xIWZ6pG6Pm0ZMEL naJojyOn7nlkXIi84xlIx5U2/0QQkiqrGbD3NudbMKAIXJYYNvHoDmg++0Vfiwpa/4 MiH+viiWVWFHoajtzbyw6tuPP8Gs+1A8RZAFp2il/Hy+95BmnKkxZrr/zWcZdl20D1 Qp/pthYqVfFHA== Date: Mon, 8 Dec 2025 16:19:55 +0900 From: Masami Hiramatsu (Google) To: qingwei hu Cc: Steven Rostedt , davem@davemloft.net, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, mhiramat@kernel.org, naveen@kernel.org, qingwei.hu@bytedance.com Subject: Re: [PATCH] kprobes: Call check_ftrace_location() on CONFIG_KPROBES_ON_FTRACE Message-Id: <20251208161955.54e2fef0fc793092a93ce88e@kernel.org> In-Reply-To: <2E248E7C-773B-4998-B059-A576163B36B0@bytedance.com> References: <20251205092933.3889547-1-qingwei.hu@bytedance.com> <20251205100823.28aa8ffd@gandalf.local.home> <2E248E7C-773B-4998-B059-A576163B36B0@bytedance.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Mon, 8 Dec 2025 14:54:33 +0800 qingwei hu wrote: > > > > 2025年12月5日 23:08，Steven Rostedt 写道： > > > > On Fri, 5 Dec 2025 17:29:33 +0800 > > "qingwei.hu" wrote: > > > >> From: Qingwei Hu > >> > >> There is a possible configuration dependency: > >> > >> KPROBES_ON_FTRACE [=n] > >> ^----- KPROBES [=y] > >> |--- HAVE_KPROBES_ON_FTRACE [=n] > >> |--- DYNAMIC_FTRACE_WITH_REGS [=n] > >> ^----- FTRACE [=y] > >> |--- DYNAMIC_FTRACE [=y] > >> |--- HAVE_DYNAMIC_FTRACE_WITH_REGS [=n] > >> > >> With DYNAMIC_FTRACE=y, ftrace_location() is meaningful and may > >> return the same address as the probe target. > >> > >> However, when KPROBES_ON_FTRACE=n, the current implementation > >> returns -EINVAL after calling check_ftrace_location(), causing > >> the validation to fail. > > > > This is a feature not a bug. > > > > The reason is if you put a kprobe on a ftrace location, it can cause ftrace > > to trigger a bug, as kprobes will modify the location and ftrace will see > > something it doesn't expect and think the system is corrupted. We don't want > > that either. > > > > If you say "KPROBES_ON_FTRACE=n" and place a kprobe on a location that is > > controlled by ftrace, it had better fail! > > > > NAK > > > > -- Steve > > Thanks for your clear explanation. I will look into other approaches > that work with this configuration. > Can you check the code under arch// implements the kprobe_ftrace_handler() correctly? if so, it should be enabled automatically. Thank you, -- Masami Hiramatsu (Google)