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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E21ABC6FD1D for ; Tue, 21 Mar 2023 15:51:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230386AbjCUPvm (ORCPT ); Tue, 21 Mar 2023 11:51:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37128 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230057AbjCUPvl (ORCPT ); Tue, 21 Mar 2023 11:51:41 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18C95497CE; Tue, 21 Mar 2023 08:51:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=0kHu/d75TtHlWBlgZ0g+45H6u2TvQunwCRm448/2BYk=; b=e91pw2BBmcICNERBe3vmWCBfMl MGcy6WWBWcRW+NqHIa69mIfI8x9EFgHbypfzZHYr40buip9CJNG3e5Hsduulgf0J/ELxtNCKxnuUb 4dGhbUfM+YHA4qdUcGrxH7Vlz2kwAF+qLlWLyzrgnuPclFdfmoQPUHirj0pJYKzEoPcHhyorWYjSz UEjac9Nvkq0H+06zhIIa5NmQ0fHsuw9O6Cs7huqRRCHFaLZik57rPz1nidtbJFFjPCNgu7o1W7KX9 55ki08KwCp/Pa2wHp2V3DhsRz7/nNY9OrVuXizMO0PT2XrMimEMIcbBW273Sg2yk5xstMaeXOVZQR 2zKfLxxw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1peeGJ-004IoW-2q; Tue, 21 Mar 2023 15:51:02 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 0884930031E; Tue, 21 Mar 2023 16:50:56 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E2FB820F030E0; Tue, 21 Mar 2023 16:50:55 +0100 (CET) Date: Tue, 21 Mar 2023 16:50:55 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: Yafang Shao , mhiramat@kernel.org, alexei.starovoitov@gmail.com, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, Andrii Nakryiko , Jiri Olsa , Josh Poimboeuf Subject: Re: [PATCH] tracing: Refuse fprobe if RCU is not watching Message-ID: <20230321155055.GA2273492@hirez.programming.kicks-ass.net> References: <20230321020103.13494-1-laoar.shao@gmail.com> <20230321101711.625d0ccb@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230321101711.625d0ccb@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org On Tue, Mar 21, 2023 at 10:17:11AM -0400, Steven Rostedt wrote: > On Tue, 21 Mar 2023 02:01:03 +0000 > Yafang Shao wrote: > > > It hits below warning on my test machine when running > > selftests/bpf/test_progs, > > > > [ 702.223611] ------------[ cut here ]------------ > > [ 702.224168] RCU not on for: preempt_count_sub+0x0/0xa0 > > [ 702.224770] WARNING: CPU: 14 PID: 5267 at include/linux/trace_recursion.h:162 fprobe_handler.part.0+0x1b8/0x1c0 > > [ 702.231740] CPU: 14 PID: 5267 Comm: main_amd64 Kdump: loaded Tainted: G O 6.2.0+ #584 > > [ 702.233169] RIP: 0010:fprobe_handler.part.0+0x1b8/0x1c0 > > [ 702.241388] Call Trace: > > [ 702.241615] > > [ 702.241811] fprobe_handler+0x22/0x30 > > [ 702.242129] 0xffffffffc04710f7 > > [ 702.242417] RIP: 0010:preempt_count_sub+0x5/0xa0 > > [ 702.242809] Code: c8 50 68 94 42 0e b5 48 cf e9 f9 fd ff ff 0f 1f 80 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 e8 4b cd 38 0b <55> 8b 0d 9c d0 cf 02 48 89 e5 85 c9 75 1b 65 8b 05 be 78 f4 4a 89 > > [ 702.244752] RSP: 0018:ffffaf6187d27f10 EFLAGS: 00000082 ORIG_RAX: 0000000000000000 > > [ 702.245801] RAX: 000000000000000e RBX: 0000000001b6ab72 RCX: 0000000000000000 > > [ 702.246804] RDX: 0000000000000000 RSI: ffffffffb627967d RDI: 0000000000000001 > > [ 702.247801] RBP: ffffaf6187d27f30 R08: 0000000000000000 R09: 0000000000000000 > > [ 702.248786] R10: 0000000000000000 R11: 0000000000000000 R12: 00000000000000ca > > [ 702.249782] R13: ffffaf6187d27f58 R14: 0000000000000000 R15: 0000000000000000 > > [ 702.250785] ? preempt_count_sub+0x5/0xa0 > > [ 702.251540] ? syscall_enter_from_user_mode+0x96/0xc0 > > [ 702.252368] ? preempt_count_sub+0x5/0xa0 > > [ 702.253104] ? syscall_enter_from_user_mode+0x96/0xc0 > > [ 702.253918] do_syscall_64+0x16/0x90 > > [ 702.254613] entry_SYSCALL_64_after_hwframe+0x72/0xdc > > [ 702.255422] RIP: 0033:0x46b793 > > > > This issue happens under CONFIG_CONTEXT_TRACKING_USER=y. When a task > > enters from user mode to kernel mode, or enters from user mode to irq, > > it excutes preempt_count_sub before RCU begins watching, and thus this > > warning is triggered. > > > > We should not handle fprobe if RCU is not watching. > > > > Suggested-by: Alexei Starovoitov > > Signed-off-by: Yafang Shao > > Cc: Alexei Starovoitov > > Cc: Andrii Nakryiko > > Cc: Jiri Olsa > > --- > > kernel/trace/fprobe.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c > > index e8143e3..fe4b248 100644 > > --- a/kernel/trace/fprobe.c > > +++ b/kernel/trace/fprobe.c > > @@ -27,6 +27,9 @@ static void fprobe_handler(unsigned long ip, unsigned long parent_ip, > > struct fprobe *fp; > > int bit; > > > > + if (!rcu_is_watching()) > > + return; > > Hmm, at least on 6.3, this should not be an issue anymore. I believe that > all locations that have ftrace callbacks should now have rcu watching? > > I think we *want* a warn on when this happens. > > Peter? You always want a wanring, because silently dropping stuff is very poor form. But yes, we must not enter tracing then RCU isn't watching, that's a fundamental fail and should be fixed.