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 426103537E0; Tue, 29 Sep 2026 00:19:16 +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=1790641159; cv=none; b=MrJKr9GzUW5Q6euuWOinOGZXZOr3h4vadI6f4j6jWAdyfMt7rcZtpkWYc7+jRQBV3O++S9r4AdpifaefaWazQ+3dy556+82tTYvG5+Zayarm9IWy2s8omZreJXVKuDvQuWjRZAY3AQpi8NnIe3vJFMnGr+99HV/0nUrr70dWySM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790641159; c=relaxed/simple; bh=f4M0na3TTgrDUfdd+Rya8TMCa7o41CInfo0IcNmDj4A=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=EoMhVhV6WEPEbeLX4lQSmh73+v0PMUxyIkI00Ra+WeFUOZP4eM9nXJGna//sEo5oMyT34wN7qZHU0cZZgQAvgxi1VQj3hgNFKS673Us7pZYUNxm8CsJLCwSgS/ENRRTDNi8trken6iH9L68CPPCx5GEhjpJ5t+N4FmHCUIWjyqY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EMMSv/+0; 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="EMMSv/+0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 45CDB1F000FF; Tue, 29 Sep 2026 00:19:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790641156; bh=h+G2VNrnKZlrsJmMOrkWRzG9gN3oOhIYpHLTvyN6bZQ=; h=From:To:Cc:Subject:Date; b=EMMSv/+0BHsi8kQS5dVPoQ80KzWDWtJfFJefsEnHikwgnayqQ9M3Q/9D4e40U75hk 9F5ttlH89ivo3S4KK775aoSeiCI4GfgGlTBeflOguW1kwVNwzP2VinCDof7qf2YRTG Xfp0LbBxMTo8CCY2riiwZ+Og3eCfgnuC923smRnOrbc9S50hq4iH3/8kH5P58Rre9k pT7GMM102oX5nKOiWBJCx8jAZW30YPY1wXF9QWDamRZ9X6LXq3YwLPT9+5JnZL5Txi +0U+ZHHBWuy6lWLOuhJdpf6gAz+fQiJmkLf4j1VtwXGCcFPVxxKwqa/h4z5sB2Fkis QXap2Rv1D66Kw== From: "Masami Hiramatsu (Google)" To: Steven Rostedt , "Paul E . McKenney" , Frederic Weisbecker , Neeraj Upadhyay Cc: Mathieu Desnoyers , Josef Bacik , Masami Hiramatsu , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, rcu@vger.kernel.org Subject: [PATCH] fprobe: Use guard(rcu_sched_notrace) and check rcu_is_watching() Date: Tue, 29 Sep 2026 09:19:12 +0900 Message-ID: <179064115227.394389.16910234241400391996.stgit@devnote2> X-Mailer: git-send-email 2.43.0 User-Agent: StGit/0.19 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="utf-8" Content-Transfer-Encoding: 8bit From: Masami Hiramatsu (Google) unregister_fprobe() and unregister_fprobe_async() (used by BPF kprobe-multi) rely on standard RCU grace periods (synchronize_rcu() and call_rcu()) to wait until in-flight fprobe handlers complete before freeing the fprobe. However, if an fprobe handler executes while RCU is not watching (such as in the idle loop or nohz_full extended quiescent states), standard RCU does not track preemption-disabled sections. Consequently, synchronize_rcu() does not wait for those executions, which can lead to a use-after-free if the fprobe is freed immediately after unregistration. Ensure handlers exit early when !rcu_is_watching(). Furthermore, fprobe_fgraph_entry() and fprobe_ftrace_entry() previously used guard(rcu)() and rcu_read_lock(), which invoke lockdep on every hit under CONFIG_PROVE_LOCKING. This adds overhead and can cause lockdep recursion if probed functions interact with lockdep. Since rhltable_lookup() and rhl_for_each_entry_rcu() use rcu_dereference_all_check() (which checks rcu_read_lock_any_held()), holding preemption disabled via rcu_read_lock_sched_notrace() is fully valid and sufficient so long as rcu_is_watching() is true. Define and use guard(rcu_sched_notrace)() across fprobe_ftrace_entry(), fprobe_fgraph_entry(), and fprobe_return(). This eliminates fast-path rcu_read_lock() and lockdep overhead while guaranteeing safe grace period synchronization. Reported-by: Sashiko Closes: https://sashiko.dev/#/bug/linux-e46bcd68-4a56-4f19-a255-e3772980e5e3 Fixes: 657b594b2084 ("fprobe: Fix unregister_fprobe() to wait for RCU grace period") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Masami Hiramatsu (Google) --- kernel/trace/fprobe.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c index 9f2d98181779..da286619c5d8 100644 --- a/kernel/trace/fprobe.c +++ b/kernel/trace/fprobe.c @@ -47,6 +47,10 @@ static struct rhltable fprobe_ip_table; static DEFINE_MUTEX(fprobe_mutex); static struct fgraph_ops fprobe_graph_ops; +DEFINE_LOCK_GUARD_0(rcu_sched_notrace, + rcu_read_lock_sched_notrace(), + rcu_read_unlock_sched_notrace()) + static u32 fprobe_node_hashfn(const void *data, u32 len, u32 seed) { return hash_ptr(*(unsigned long **)data, 32); @@ -329,16 +333,14 @@ static void fprobe_ftrace_entry(unsigned long ip, unsigned long parent_ip, struct fprobe *fp; int bit; + if (!rcu_is_watching()) + return; + bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; - /* - * ftrace_test_recursion_trylock() disables preemption, but - * rhltable_lookup() checks whether rcu_read_lcok is held. - * So we take rcu_read_lock() here. - */ - rcu_read_lock(); + guard(rcu_sched_notrace)(); head = rhltable_lookup(&fprobe_ip_table, &ip, fprobe_rht_params); rhl_for_each_entry_rcu(node, pos, head, hlist) { @@ -353,7 +355,6 @@ static void fprobe_ftrace_entry(unsigned long ip, unsigned long parent_ip, else __fprobe_handler(ip, parent_ip, fp, fregs, NULL); } - rcu_read_unlock(); ftrace_test_recursion_unlock(bit); } NOKPROBE_SYMBOL(fprobe_ftrace_entry); @@ -567,10 +568,13 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops struct fprobe *fp; int used, ret; + if (!rcu_is_watching()) + return 0; + if (WARN_ON_ONCE(!fregs)) return 0; - guard(rcu)(); + guard(rcu_sched_notrace)(); head = rhltable_lookup(&fprobe_ip_table, &func, fprobe_rht_params); reserved_words = 0; rhl_for_each_entry_rcu(node, pos, head, hlist) { @@ -665,13 +669,16 @@ static void fprobe_return(struct ftrace_graph_ret *trace, int size, curr; int size_words; + if (!rcu_is_watching()) + return; + fgraph_data = (unsigned long *)fgraph_retrieve_data(gops->idx, &size); if (WARN_ON_ONCE(!fgraph_data)) return; size_words = SIZE_IN_LONG(size); ret_ip = ftrace_regs_get_instruction_pointer(fregs); - preempt_disable_notrace(); + guard(rcu_sched_notrace)(); curr = 0; while (size_words > curr) { @@ -687,7 +694,6 @@ static void fprobe_return(struct ftrace_graph_ret *trace, } curr += size; } - preempt_enable_notrace(); } NOKPROBE_SYMBOL(fprobe_return);