From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F66FC388F7 for ; Tue, 3 Nov 2020 05:39:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5BDAA2227F for ; Tue, 3 Nov 2020 05:39:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604381983; bh=Q076BhLY0DjbtliwCu3GQaRyBU42Z/sESEIdo+7CCzE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=x0g07T8Rhi9Y/pjinf2AnjePsYlRZp17PxMj5+RKi3rF6ZA3gZaO9woDTs30GirUk l84+8bUBsZDfofR2qN4XRjTB9jdPLEcfV2t1vgP3f/b6gXhBroaoOdmUYbnP81B1Th GWn4z4Q5LzOx47rIxB2B7Tu326pmf1Ogd2sNPfqc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725997AbgKCFjn (ORCPT ); Tue, 3 Nov 2020 00:39:43 -0500 Received: from mail.kernel.org ([198.145.29.99]:49692 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725958AbgKCFjm (ORCPT ); Tue, 3 Nov 2020 00:39:42 -0500 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F22EC22277; Tue, 3 Nov 2020 05:39:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604381982; bh=Q076BhLY0DjbtliwCu3GQaRyBU42Z/sESEIdo+7CCzE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=wXLsZJezLTss4VZf3uN/AvI46+E1z5Odjbvi+BURO54maOx6U+UQ2wefCCzSow2na 19n2QkXSlNBlOyUVmUmLCyaGmJEfltTAICNSS8PI8jIlpvD2qNHyrgSoRfaQnxcHG6 yyIKsbDtuUB0s4jDE2XaDgQxIm4o16orrtVO7jfM= Date: Tue, 3 Nov 2020 14:39:38 +0900 From: Masami Hiramatsu To: Steven Rostedt Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Peter Zijlstra , Eddy_Wu@trendmicro.com, x86@kernel.org, davem@davemloft.net, naveen.n.rao@linux.ibm.com, anil.s.keshavamurthy@intel.com, linux-arch@vger.kernel.org, cameron@moodycamel.com, oleg@redhat.com, will@kernel.org, paulmck@kernel.org Subject: Re: [PATCH v5 14/21] kprobes: Remove NMI context check Message-Id: <20201103143938.704c7974e93c854511580c38@kernel.org> In-Reply-To: <20201102092726.57cb643f@gandalf.local.home> References: <159870598914.1229682.15230803449082078353.stgit@devnote2> <159870615628.1229682.6087311596892125907.stgit@devnote2> <20201030213831.04e81962@oasis.local.home> <20201102141138.1fa825113742f3bea23bc383@kernel.org> <20201102145334.23d4ba691c13e0b6ca87f36d@kernel.org> <20201102160234.fa0ae70915ad9e2b21c08b85@kernel.org> <20201102092726.57cb643f@gandalf.local.home> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Mon, 2 Nov 2020 09:27:26 -0500 Steven Rostedt wrote: > > [ Peter Z, please take a look a this ] > > On Mon, 2 Nov 2020 16:02:34 +0900 > Masami Hiramatsu wrote: > > > >From 509b27efef8c7dbf56cab2e812916d6cd778c745 Mon Sep 17 00:00:00 2001 > > From: Masami Hiramatsu > > Date: Mon, 2 Nov 2020 15:37:28 +0900 > > Subject: [PATCH] kprobes: Disable lockdep for kprobe busy area > > > > Since the code area in between kprobe_busy_begin()/end() prohibits > > other kprobs to call probe handlers, we can avoid inconsitent > > locks there. But lockdep doesn't know that, so it warns rp->lock > > or kretprobe_table_lock. > > > > To supress those false-positive errors, disable lockdep while > > kprobe_busy is set. > > > > Signed-off-by: Masami Hiramatsu > > --- > > kernel/kprobes.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > index 8a12a25fa40d..c7196e583600 100644 > > --- a/kernel/kprobes.c > > +++ b/kernel/kprobes.c > > @@ -1295,10 +1295,12 @@ void kprobe_busy_begin(void) > > __this_cpu_write(current_kprobe, &kprobe_busy); > > kcb = get_kprobe_ctlblk(); > > kcb->kprobe_status = KPROBE_HIT_ACTIVE; > > + lockdep_off(); > > } > > > > void kprobe_busy_end(void) > > { > > + lockdep_on(); > > __this_cpu_write(current_kprobe, NULL); > > preempt_enable(); > > } > > -- > > No, this is not the correct workaround (too big of a hammer). You could do > the following: > > From 4139d9c8437b0bd2262e989ca4eb0a83b7e7bb72 Mon Sep 17 00:00:00 2001 > From: "Steven Rostedt (VMware)" > Date: Mon, 2 Nov 2020 09:17:49 -0500 > Subject: [PATCH] kprobes: Tell lockdep about kprobe nesting > > Since the kprobe handlers have protection that prohibits other handlers from > executing in other contexts (like if an NMI comes in while processing a > kprobe, and executes the same kprobe, it will get fail with a "busy" > return). Lockdep is unaware of this protection. Use lockdep's nesting api to > differentiate between locks taken in NMI context and other context to > supress the false warnings. Ah, OK. This looks good to me. BTW, in_nmi() in pre_handler_kretprobe() always be true because now int3 is treated as an NMI. So you can always pass 1 there. Acked-by: Masami Hiramatsu Thank you, > > Link: https://lore.kernel.org/r/20201102160234.fa0ae70915ad9e2b21c08b85@kernel.org > > Cc: Peter Zijlstra > Signed-off-by: Steven Rostedt (VMware) > --- > kernel/kprobes.c | 24 ++++++++++++++++++++---- > 1 file changed, 20 insertions(+), 4 deletions(-) > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index 8a12a25fa40d..ccb285867059 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -1249,7 +1249,12 @@ __acquires(hlist_lock) > > *head = &kretprobe_inst_table[hash]; > hlist_lock = kretprobe_table_lock_ptr(hash); > - raw_spin_lock_irqsave(hlist_lock, *flags); > + /* > + * Nested is a workaround that will soon not be needed. > + * There's other protections that make sure the same lock > + * is not taken on the same CPU that lockdep is unaware of. > + */ > + raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi()); > } > NOKPROBE_SYMBOL(kretprobe_hash_lock); > > @@ -1258,7 +1263,12 @@ static void kretprobe_table_lock(unsigned long hash, > __acquires(hlist_lock) > { > raw_spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash); > - raw_spin_lock_irqsave(hlist_lock, *flags); > + /* > + * Nested is a workaround that will soon not be needed. > + * There's other protections that make sure the same lock > + * is not taken on the same CPU that lockdep is unaware of. > + */ > + raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi()); > } > NOKPROBE_SYMBOL(kretprobe_table_lock); > > @@ -2025,10 +2035,16 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs) > struct kretprobe *rp = container_of(p, struct kretprobe, kp); > unsigned long hash, flags = 0; > struct kretprobe_instance *ri; > + int nmi = !!in_nmi(); > > /* TODO: consider to only swap the RA after the last pre_handler fired */ > hash = hash_ptr(current, KPROBE_HASH_BITS); > - raw_spin_lock_irqsave(&rp->lock, flags); > + /* > + * Nested is a workaround that will soon not be needed. > + * There's other protections that make sure the same lock > + * is not taken on the same CPU that lockdep is unaware of. > + */ > + raw_spin_lock_irqsave_nested(&rp->lock, flags, nmi); > if (!hlist_empty(&rp->free_instances)) { > ri = hlist_entry(rp->free_instances.first, > struct kretprobe_instance, hlist); > @@ -2039,7 +2055,7 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs) > ri->task = current; > > if (rp->entry_handler && rp->entry_handler(ri, regs)) { > - raw_spin_lock_irqsave(&rp->lock, flags); > + raw_spin_lock_irqsave_nested(&rp->lock, flags, nmi); > hlist_add_head(&ri->hlist, &rp->free_instances); > raw_spin_unlock_irqrestore(&rp->lock, flags); > return 0; > -- > 2.25.4 > -- Masami Hiramatsu