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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AA710C433EF for ; Fri, 5 Nov 2021 13:21:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 873DB6103B for ; Fri, 5 Nov 2021 13:21:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232823AbhKENXy (ORCPT ); Fri, 5 Nov 2021 09:23:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:35928 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231149AbhKENXv (ORCPT ); Fri, 5 Nov 2021 09:23:51 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (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 4DBF5610FD; Fri, 5 Nov 2021 13:21:11 +0000 (UTC) Date: Fri, 5 Nov 2021 09:21:08 -0400 From: Steven Rostedt To: Thomas Gleixner Cc: syzbot , john.stultz@linaro.org, linux-kernel@vger.kernel.org, sboyd@kernel.org, syzkaller-bugs@googlegroups.com, Peter Zijlstra , Mark Rutland , Steven Rostedt , Alexei Starovoitov , Daniel Borkmann Subject: Re: [syzbot] possible deadlock in ktime_get_coarse_ts64 Message-ID: <20211105092108.71cd14ac@gandalf.local.home> In-Reply-To: <87lf224uki.ffs@tglx> References: <00000000000013aebd05cff8e064@google.com> <87lf224uki.ffs@tglx> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; 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-kernel@vger.kernel.org On Fri, 05 Nov 2021 14:10:21 +0100 Thomas Gleixner wrote: > > -> #0 (tk_core.seq.seqcount){----}-{0:0}: > > check_prev_add kernel/locking/lockdep.c:3051 [inline] > > check_prevs_add kernel/locking/lockdep.c:3174 [inline] > > validate_chain+0x1dfb/0x8240 kernel/locking/lockdep.c:3789 > > __lock_acquire+0x1382/0x2b00 kernel/locking/lockdep.c:5015 > > lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5625 > > seqcount_lockdep_reader_access+0xfe/0x230 include/linux/seqlock.h:103 > > ktime_get_coarse_ts64+0x25/0x110 kernel/time/timekeeping.c:2255 > > ktime_get_coarse include/linux/timekeeping.h:120 [inline] > > ktime_get_coarse_ns include/linux/timekeeping.h:126 [inline] > > --> this call is invalid > > > ____bpf_ktime_get_coarse_ns kernel/bpf/helpers.c:173 [inline] > > bpf_ktime_get_coarse_ns+0x7e/0x130 kernel/bpf/helpers.c:171 > > bpf_prog_a99735ebafdda2f1+0x10/0xb50 > > bpf_dispatcher_nop_func include/linux/bpf.h:721 [inline] > > __bpf_prog_run include/linux/filter.h:626 [inline] > > bpf_prog_run include/linux/filter.h:633 [inline] > > BPF_PROG_RUN_ARRAY include/linux/bpf.h:1294 [inline] > > trace_call_bpf+0x2cf/0x5d0 kernel/trace/bpf_trace.c:127 > > perf_trace_run_bpf_submit+0x7b/0x1d0 kernel/events/core.c:9708 > > perf_trace_lock+0x37c/0x440 include/trace/events/lock.h:39 > > trace_lock_release+0x128/0x150 include/trace/events/lock.h:58 > > Timestamps from within a tracepoint can only be taken with: > > 1) jiffies > 2) sched_clock() > 3) ktime_get_*_fast_ns() This is why we have tracing clocks: include/linux/trace_clock.h: trace_clock_local() trace_clock() trace_clock_jiffies() trace_clock_global() trace_clock_counter() And perf uses its own clock, which is either local_clock() or one of the ktime_get_*_ns() clocks. -- Steve > > Those are NMI safe and can be invoked from anywhere. > > All other time getters which have to use the timekeeping seqcount > protection are prone to live locks and _cannot_ be used from > tracepoints ever. > > This restriction exists since day one of tracepoints and is not > magically going away for BPF.