From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 A075F37F725; Thu, 30 Jul 2026 03:38:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785382721; cv=none; b=ZviLvJxeKPmh9KVT1RW5peq4Evero8dN64jcjqOuFpCHr+cQFKLh+G03QH6HQWV+CVdEfUKXQ7HtOhY9wktnljzcHz3pzrRFnJAyIMKIHe1/bFIRqc3Qc9NVfenF7hPfVBgUVPowjo/q3eIb8ZcC0HmkpwjO6hX38RRChwW66Q4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785382721; c=relaxed/simple; bh=ZjdlBuT83fWwIskIVoyRm6bAu1/lFcLL0bxBZmascIo=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=QJnweOY8M7k+7cjyCSmBKETHjEFpsVtAmGk6/tmSDHX8SSDzM/W99xPiooOWK0yY0jsybhHipzIXRzfJuo+XxcfWOK7JONBB525GQseeZ7ROOvS4t1b4iqZeRWDHEr+diU75m22/Huy0j5FeljFWP6ENKE2jMJjVt0QFW0pfD1k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kCOXLv9m; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kCOXLv9m" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E18C1F000E9; Thu, 30 Jul 2026 03:38:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785382720; bh=wEfJUHAwyyexkwLVITbPZO8WKWBL8aoa0QA+h6kjDuQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=kCOXLv9mPWutBPKVeNn94NEnRK7xPG8U+DAsJs1C7M4u+LW2U9CUi9zFzW3S4+yiD nrEAHlhAnIAixJDFrFLDm18MJ5LTEt/JggYEwUl6T5vVOyherdN3dHsCC2/NkxY24N e7e9EIQDhzMUzrgg8PVCC+KH01QjudYwLf3lo0TBpRZTKweI3nrc/EunPeLOzoS7Qc 00q2GFilnW8G35sguS5zgodrjMbTfI0JdKUmFYwFMIKoeOvJQXGqAhPgc3EVRgSXJc MO+dylj5Dd8Un8t7GwI7Yex8x8H2H7o5DIxUmkfjj61KKrx9Y70BYCOGtV7TucM09b O0Mhsf05O0Ksw== Date: Thu, 30 Jul 2026 12:38:35 +0900 From: Masami Hiramatsu (Google) To: "Masami Hiramatsu (Google)" Cc: Oleg Nesterov , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , James Clark , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org Subject: Re: [PATCH] uprobes: Remove redundant guard(rcu) in find_active_uprobe_speculative() Message-Id: <20260730123835.e94483b966bc7cfcd5645e79@kernel.org> In-Reply-To: <178537593930.153254.1296986092000402239.stgit@devnote2> References: <178537593930.153254.1296986092000402239.stgit@devnote2> 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, 30 Jul 2026 10:45:39 +0900 "Masami Hiramatsu (Google)" wrote: > From: Masami Hiramatsu (Google) > > find_active_uprobe_speculative() is called from find_active_uprobe_rcu(), > which is invoked by handle_swbp() and handle_syscall_uprobe(). > Both callers already hold RCU Tasks Trace (via rcu_read_lock_trace() or > guard(rcu_tasks_trace)()). > > Calling guard(rcu)() inside find_active_uprobe_speculative() is redundant > because the caupller already guarantees RCU Tasks Trace protection. > Furthermore, standard RCU (rcu_read_lock()) does not protect uprobes_tree > against asynchronous uprobe destruction (call_rcu_tasks_trace()). > > Remove the redundant guard(rcu)() from find_active_uprobe_speculative() and > replace it with lockdep_assert(rcu_read_lock_trace_held()) and a comment > documenting that callers must hold RCU Tasks Trace protection, matching the > convention used by find_active_uprobe_rcu() and find_uprobe_rcu(). > > Fixes: e0925f2dc4de ("uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution") > Assisted-by: Antigravity:gemini-3.6-flash > Signed-off-by: Masami Hiramatsu (Google) Sashiko mentioned that this guard is not for uprobes_tree, but VMA lookup. Please ignore this. Thanks, > --- > kernel/events/uprobes.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > index 4084e926e284..b4e253d43b30 100644 > --- a/kernel/events/uprobes.c > +++ b/kernel/events/uprobes.c > @@ -2424,6 +2424,7 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) > return is_trap_insn(&opcode); > } > > +/* assumes being inside RCU Tasks Trace protected region */ > static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr) > { > struct mm_struct *mm = current->mm; > @@ -2433,7 +2434,7 @@ static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr) > loff_t offset; > unsigned int seq; > > - guard(rcu)(); > + lockdep_assert(rcu_read_lock_trace_held()); > > if (!mmap_lock_speculate_try_begin(mm, &seq)) > return NULL; > -- Masami Hiramatsu (Google)