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 A4E46C433F5 for ; Fri, 5 Nov 2021 13:10:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CE2A61054 for ; Fri, 5 Nov 2021 13:10:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232656AbhKENND (ORCPT ); Fri, 5 Nov 2021 09:13:03 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:40764 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229924AbhKENNC (ORCPT ); Fri, 5 Nov 2021 09:13:02 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1636117821; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=TPWC8jQewkfGDLEH4jppRovKUEtYI9LoKKxunmdFFp4=; b=YuJx8f4PO4KHawMFpwrQqQLb43VmEusfoO3IafxTEPGnpMxFeiVJ98Go9vVpVWoIhT+CQE g3lpxsaldOxQUfskm1w7TfejSstPlHynR3FmwxBzghPsW0728Pflc7TbhwMYiNd6zTz0Ys d4V2PVOJ1OcysqyuTCqmv1uiXJz41astHUzrFZNMTH/N71Qqygeipn0nSTTI0f7ZRWVwHC XU3mr1NOo50kkeEVjfI767/zqbCN16pMxqZ+Lsr/uRCZgMMd64+OszrtazcCzuM1+69dkb ubMdqjp5MImiONVDyXMQSowN1mxnTNDJTrC+BZ/L6qaetplCbdlmQKCgRbHe3A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1636117821; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=TPWC8jQewkfGDLEH4jppRovKUEtYI9LoKKxunmdFFp4=; b=RbjR10L46Uuairuw6Z0qnsDknHuc3Xevd+A33nbWZ0r1InJE3s9L9RrqrKoC0X/fRCN9CC t+sW/RB7ZqrTtfBA== To: 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 In-Reply-To: <00000000000013aebd05cff8e064@google.com> References: <00000000000013aebd05cff8e064@google.com> Date: Fri, 05 Nov 2021 14:10:21 +0100 Message-ID: <87lf224uki.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 04 2021 at 09:18, syzbot wrote: > syzbot found the following issue on: > > HEAD commit: dcd68326d29b Merge tag 'devicetree-for-5.16' of git://git... > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=14a3576ab00000 > kernel config: https://syzkaller.appspot.com/x/.config?x=a89cd86e20989871 > dashboard link: https://syzkaller.appspot.com/bug?extid=43fd005b5a1b4d10781e > compiler: Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2 > > Unfortunately, I don't have any reproducer for this issue yet. No need to look for an reproducer. The wreckage is entirely clear. > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+43fd005b5a1b4d10781e@syzkaller.appspotmail.com > > ====================================================== > WARNING: possible circular locking dependency detected > 5.15.0-syzkaller #0 Not tainted > ------------------------------------------------------ > syz-executor.4/14877 is trying to acquire lock: > ffffffff8cb30008 (tk_core.seq.seqcount){----}-{0:0}, at: ktime_get_coarse_ts64+0x25/0x110 kernel/time/timekeeping.c:2255 > > but task is already holding lock: > ffffffff90dbf200 (&obj_hash[i].lock){-.-.}-{2:2}, at: debug_object_deactivate+0x61/0x400 lib/debugobjects.c:735 > > which lock already depends on the new lock. Actually it does not matter at all which lock is held. The wreckage is more fundamental. > the existing dependency chain (in reverse order) is: > > -> #1 (&obj_hash[i].lock){-.-.}-{2:2}: > lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5625 > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] > _raw_spin_lock_irqsave+0xd1/0x120 kernel/locking/spinlock.c:162 > __debug_object_init+0xd9/0x1860 lib/debugobjects.c:569 > debug_hrtimer_init kernel/time/hrtimer.c:414 [inline] > debug_init kernel/time/hrtimer.c:468 [inline] > hrtimer_init+0x20/0x40 kernel/time/hrtimer.c:1592 > ntp_init_cmos_sync kernel/time/ntp.c:676 [inline] > ntp_init+0xa1/0xad kernel/time/ntp.c:1095 > timekeeping_init+0x512/0x6bf kernel/time/timekeeping.c:1639 > start_kernel+0x267/0x56e init/main.c:1030 > secondary_startup_64_no_verify+0xb1/0xbb > > -> #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() 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. Thanks, tglx