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 6499C2115; Thu, 18 Jan 2024 02:25:32 +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=1705544732; cv=none; b=ZZ9Mz7xeV4epI1hQ4y4+B9tm+XhINDHNw7xdm2+MUKi3iFno7IsqhkZwckFw/9xO7LMSoFuR5VYwSBgu8fqKmVMkoTS0i6C67Kkl/EH/3Bu3RH+QV7y1SfIYUSUzjPW54w4vQch2rqjy+Lm2/Zy8+C2joOeSTO2nrBQkbGUiLUY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1705544732; c=relaxed/simple; bh=8LBkJof5B327L1V0yCKArqI09jJkUVrtza9uTR4uueI=; h=Received:Date:From:To:Cc:Subject:Message-ID:In-Reply-To: References:X-Mailer:MIME-Version:Content-Type: Content-Transfer-Encoding; b=Hj4KJGrw7UpTZ1sfuohhyUu4JQWyixFoSpVtUKTwjQHAz6R7L2u3Z32Tkkh9a7FMSDrrdwiIMXZckDyAXkI5X5AiZ9GudKNHJkYEB8X+xcZ22U51on4dGnUG8vDS5foFAFcSOsUiU2fJxJwh1FbUB48r9GL9VF3Dn8tU+iPdRLU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 633BFC433C7; Thu, 18 Jan 2024 02:25:29 +0000 (UTC) Date: Wed, 17 Jan 2024 21:26:46 -0500 From: Steven Rostedt To: Chen Zhongjin Cc: , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2] kprobes: Use synchronize_rcu_tasks_rude in kprobe_optimizer Message-ID: <20240117212646.5f0ddf0c@gandalf.local.home> In-Reply-To: <20240118021842.290665-1-chenzhongjin@huawei.com> References: <20240118021842.290665-1-chenzhongjin@huawei.com> X-Mailer: Claws Mail 3.19.1 (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, 18 Jan 2024 02:18:42 +0000 Chen Zhongjin wrote: > There is a deadlock scenario in kprobe_optimizer(): > > pid A pid B pid C > kprobe_optimizer() do_exit() perf_kprobe_init() > mutex_lock(&kprobe_mutex) exit_tasks_rcu_start() mutex_lock(&kprobe_mutex) > synchronize_rcu_tasks() zap_pid_ns_processes() // waiting kprobe_mutex > // waiting tasks_rcu_exit_srcu kernel_wait4() > // waiting pid C exit > > To avoid this deadlock loop, use synchronize_rcu_tasks_rude() in kprobe_optimizer() > rather than synchronize_rcu_tasks(). synchronize_rcu_tasks_rude() can also promise > that all preempted tasks have scheduled, but it will not wait tasks_rcu_exit_srcu. > Did lockdep detect this? If not, we should fix that. I'm also thinking if we should find another solution, as this seems more of a work around than a fix. > Fixes: a30b85df7d59 ("kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y") > Signed-off-by: Chen Zhongjin > --- > v1 -> v2: Add Fixes tag > --- > arch/Kconfig | 2 +- > kernel/kprobes.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/Kconfig b/arch/Kconfig > index f4b210ab0612..dc6a18854017 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -104,7 +104,7 @@ config STATIC_CALL_SELFTEST > config OPTPROBES > def_bool y > depends on KPROBES && HAVE_OPTPROBES > - select TASKS_RCU if PREEMPTION > + select TASKS_RUDE_RCU Is this still a bug if PREEMPTION is not enabled? -- Steve > > config KPROBES_ON_FTRACE > def_bool y > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index d5a0ee40bf66..09056ae50c58 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -623,7 +623,7 @@ static void kprobe_optimizer(struct work_struct *work) > * Note that on non-preemptive kernel, this is transparently converted > * to synchronoze_sched() to wait for all interrupts to have completed. > */ > - synchronize_rcu_tasks(); > + synchronize_rcu_tasks_rude(); > > /* Step 3: Optimize kprobes after quiesence period */ > do_optimize_kprobes();