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 02C1E360B1; Thu, 11 Jan 2024 13:47:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Otuorx5P" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8D947C433C7; Thu, 11 Jan 2024 13:47:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1704980846; bh=VmYIuHNFpAz3LOz9NBDiJCUeFlaLSYys+F8WdobNIWw=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Otuorx5P1ZH+ifPjHawCm0vkd+0hzqgsloxeS60G75hlMfsHHww6a2ZKKRJm2dUVR mXDpLoqwenyisqT9aP3L2+qViHBsFZW15X8WxyclbXTD+91bFsaKxNatFGGmg7m6vJ LSMmmDmIenIuz2aNFCjrdoN0AOx8C22c9B8PAXXEpt13N7CbcyCGMBaxthC5zb0C+h cYfdac8ERIJ9dnuff5R2KCm3xdnqjXq/qz0tul35ujIQbPqD1d8fjgHqOw/FXxJhOT 6CuhPSYa6SVAFUZBXH3zynca1S9X5twmQG0uZO7aeUaP3OQeOapXjq37+lJTdCrJ3/ mqfSR80rUzdjQ== Date: Thu, 11 Jan 2024 22:47:20 +0900 From: Masami Hiramatsu (Google) To: Mark Rutland Cc: Alexei Starovoitov , Steven Rostedt , Florent Revest , linux-trace-kernel@vger.kernel.org, LKML , Martin KaFai Lau , bpf , Sven Schnelle , Alexei Starovoitov , Jiri Olsa , Arnaldo Carvalho de Melo , Daniel Borkmann , Alan Maguire , Peter Zijlstra , Thomas Gleixner , Guo Ren Subject: Re: [PATCH v5 11/34] function_graph: Have the instances use their own ftrace_ops for filtering Message-Id: <20240111224720.12d2062d360641be25deb9d2@kernel.org> In-Reply-To: References: <170290509018.220107.1347127510564358608.stgit@devnote2> <170290522555.220107.1435543481968270637.stgit@devnote2> <20240108101436.07509def635fbecf80a59ae6@kernel.org> X-Mailer: Sylpheed 3.7.0 (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=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 8 Jan 2024 15:03:21 +0000 Mark Rutland wrote: > On Mon, Jan 08, 2024 at 02:21:03PM +0000, Mark Rutland wrote: > > On Mon, Jan 08, 2024 at 12:25:55PM +0000, Mark Rutland wrote: > > > We also have HAVE_FUNCTION_GRAPH_RET_ADDR_PTR, but since the return address is > > > not on the stack at the point function-entry is intercepted we use the FP as > > > the retp value -- in the absence of tail calls this will be different between a > > > caller and callee. > > > > Ah; I just spotted that this patch changed that in ftrace_graph_func(), which > > is the source of the bug. > > > > As of this patch, we use the address of fregs->lr as the retp value, but the > > unwinder still uses the FP value, and so when unwind_recover_return_address() > > calls ftrace_graph_ret_addr(), the retp value won't match the expected entry on > > the fgraph ret_stack, resulting in failing to find the expected entry. > > > > Since the ftrace_regs only exist transiently during function entry/exit, it's > > possible for a stackframe to reuse that same address on the stack, which would > > result in finding a different entry by mistake. > > > > The diff below restores the existing behaviour and fixes the issue for me. > > Could you please fold that into this patch? > > > > On a separate note, looking at how this patch changed arm64's > > ftrace_graph_func(), do we need similar changes to arm64's > > prepare_ftrace_return() for the old-style mcount based ftrace? > > > > Mark. > > > > ---->8---- > > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > > index 205937e04ece..329092ce06ba 100644 > > --- a/arch/arm64/kernel/ftrace.c > > +++ b/arch/arm64/kernel/ftrace.c > > @@ -495,7 +495,7 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, > > if (bit < 0) > > return; > > > > - if (!function_graph_enter_ops(*parent, ip, fregs->fp, parent, gops)) > > + if (!function_graph_enter_ops(*parent, ip, fregs->fp, (void *)fregs->fp, gops)) > > *parent = (unsigned long)&return_to_handler; > > > > ftrace_test_recursion_unlock(bit); > > Thinking some more, this line gets excessively long when we pass the fregs too, > so it's probably worth adding a local variable for fp, i.e. the diff below. Yeah, that will be better to keep the line short. Thank you, > > Mark. > > ---->8---- > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index 205937e04ece..d4e142ef4686 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -481,8 +481,9 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, > void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, > struct ftrace_ops *op, struct ftrace_regs *fregs) > { > - unsigned long *parent = &fregs->lr; > struct fgraph_ops *gops = container_of(op, struct fgraph_ops, ops); > + unsigned long *parent = &fregs->lr; > + unsigned long fp = fregs->fp; > int bit; > > if (unlikely(ftrace_graph_is_dead())) > @@ -495,7 +496,7 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip, > if (bit < 0) > return; > > - if (!function_graph_enter_ops(*parent, ip, fregs->fp, parent, gops)) > + if (!function_graph_enter_ops(*parent, ip, fp, (void *)fp, gops)) > *parent = (unsigned long)&return_to_handler; > > ftrace_test_recursion_unlock(bit); > -- Masami Hiramatsu (Google)