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 EB0173C0C; Fri, 5 Sep 2025 05:33:40 +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=1757050421; cv=none; b=m1ILTMvHGT4eR5R97yT4deYT+CIHmz/F1gcbC0h2WqZcI7pwtBJa6DX4fRL5HJ+K1BgPYSnE+j8s2+fB8zaeLfmspwIxwUxyofO0KdEssC6NdhtDrEJeBKuKFc6BkrSrso9w2W23auXR1O7LNSDCLj1QgIim60k6QGHQpt7UJBM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757050421; c=relaxed/simple; bh=z6ZMhChpG/YjKZS440yz+21mwMCNkfqayALs77Q0EQA=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=qSEAvETYxnH1WVjgeWdrbkHr9S2jnMQPuhJzCM1WL9uskIkHkMAF+02BnCbTsuKaaijIaeCbO1an1AqwORDxaNVoYFxzn4SbLjsE0TCzVUtSD6DyZKagyDL9JcRoUCP2QEvxl+kfnWUQEUN/kRjYa58QqPm1tF3kvvndvzqRTec= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CiDul2kz; 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="CiDul2kz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DDD23C4CEF1; Fri, 5 Sep 2025 05:33:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1757050420; bh=z6ZMhChpG/YjKZS440yz+21mwMCNkfqayALs77Q0EQA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=CiDul2kz3sf2fndz0v+IGj3QJ0y/eWJiL59tZWvonRIowXikUWWZNCT5SkT9JAicT pqOOf3maR7b5RVO6pGSnViqLRyLCCe8adIK1psw/sepYsFtVkoQsZvk9jnIBk97XtE j4/Oj3na5fG5eACMv2SnbdYN0Pyd6Icxm+/OQnZB/Q0JjGyghesXrHcb8D+HINudTo CwvZ6jARkwiyApKEghTmS5Xqi1IRgYKatL28ws7m8fVYrnPunMVqPQqAhFgW3RXUYF jO5QICZID3bPYUrqmwzPQcdCYLXwa7sM+m7H+C0AVBOjMd+OHpFfVx6YVju/HIp+aK wM58xhHKVYs4A== Date: Fri, 5 Sep 2025 14:33:36 +0900 From: Masami Hiramatsu (Google) To: Menglong Dong Cc: rostedt@goodmis.org, mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v2] tracing: fprobe: fix suspicious rcu usage in fprobe_entry Message-Id: <20250905143336.85682a1443ed998137bee0b7@kernel.org> In-Reply-To: <20250904062729.151931-1-dongml2@chinatelecom.cn> References: <20250904062729.151931-1-dongml2@chinatelecom.cn> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-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 Thu, 4 Sep 2025 14:27:29 +0800 Menglong Dong wrote: > rcu_read_lock() is not needed in fprobe_entry, but rcu_dereference_check() > is used in rhltable_lookup(), which causes suspicious RCU usage warning: > > WARNING: suspicious RCU usage > 6.17.0-rc1-00001-gdfe0d675df82 #1 Tainted: G S > ----------------------------- > include/linux/rhashtable.h:602 suspicious rcu_dereference_check() usage! > ...... > stack backtrace: > CPU: 1 UID: 0 PID: 4652 Comm: ftracetest Tainted: G S > Tainted: [S]=CPU_OUT_OF_SPEC, [I]=FIRMWARE_WORKAROUND > Hardware name: Dell Inc. OptiPlex 7040/0Y7WYT, BIOS 1.1.1 10/07/2015 > Call Trace: > > dump_stack_lvl+0x7c/0x90 > lockdep_rcu_suspicious+0x14f/0x1c0 > __rhashtable_lookup+0x1e0/0x260 > ? __pfx_kernel_clone+0x10/0x10 > fprobe_entry+0x9a/0x450 > ? __lock_acquire+0x6b0/0xca0 > ? find_held_lock+0x2b/0x80 > ? __pfx_fprobe_entry+0x10/0x10 > ? __pfx_kernel_clone+0x10/0x10 > ? lock_acquire+0x14c/0x2d0 > ? __might_fault+0x74/0xc0 > function_graph_enter_regs+0x2a0/0x550 > ? __do_sys_clone+0xb5/0x100 > ? __pfx_function_graph_enter_regs+0x10/0x10 > ? _copy_to_user+0x58/0x70 > ? __pfx_kernel_clone+0x10/0x10 > ? __x64_sys_rt_sigprocmask+0x114/0x180 > ? __pfx___x64_sys_rt_sigprocmask+0x10/0x10 > ? __pfx_kernel_clone+0x10/0x10 > ftrace_graph_func+0x87/0xb0 > > As we discussed in [1], fix this by using guard(rcu)() in fprobe_entry() > to protect the rhltable_lookup() and rhl_for_each_entry_rcu() with > rcu_read_lock and suppress this warning. > > Link: https://lore.kernel.org/all/20250829021436.19982-1-dongml2@chinatelecom.cn/ [1] > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-lkp/202508281655.54c87330-lkp@intel.com > Fixes: dfe0d675df82 ("tracing: fprobe: use rhltable for fprobe_ip_table") > Signed-off-by: Menglong Dong Looks good to me. Let me pick this to probes/for-next. Thanks! > --- > v2: > - use guard(rcu)() instead of rcu_read_lock() > --- > kernel/trace/fprobe.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > index fb127fa95f21..6a205903b1ed 100644 > --- a/kernel/trace/fprobe.c > +++ b/kernel/trace/fprobe.c > @@ -269,6 +269,7 @@ static int fprobe_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops, > if (WARN_ON_ONCE(!fregs)) > return 0; > > + guard(rcu)(); > head = rhltable_lookup(&fprobe_ip_table, &func, fprobe_rht_params); > reserved_words = 0; > rhl_for_each_entry_rcu(node, pos, head, hlist) { > -- > 2.51.0 > -- Masami Hiramatsu (Google)