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 321A0C433FE for ; Tue, 29 Nov 2022 17:23:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236605AbiK2RX3 (ORCPT ); Tue, 29 Nov 2022 12:23:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55814 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236598AbiK2RX0 (ORCPT ); Tue, 29 Nov 2022 12:23:26 -0500 Received: from mail-qk1-x730.google.com (mail-qk1-x730.google.com [IPv6:2607:f8b0:4864:20::730]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B10468C5A; Tue, 29 Nov 2022 09:23:25 -0800 (PST) Received: by mail-qk1-x730.google.com with SMTP id c2so10299079qko.1; Tue, 29 Nov 2022 09:23:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :feedback-id:from:to:cc:subject:date:message-id:reply-to; bh=7jlcVHL9xXutHyudxpWgmNyuiG9QsSh1Xo0dK9zsWjA=; b=Nov5hLqCze7EZR8kEb6NBupeNB9jWyAdl6Dw9hSGGMGGm5OPqU/mgPXzGOvCl/88ut mD5GIuQXdKYrHvtkj18slwPS+RDLfkmA38senKJMfjzBQr0bZBDvIR46UycvRsPFmamo 5qthavMLzepH+BTZs+rMYsZbXMnIUtGejX3VhvI8OPqDFXBLqRkBc9vinLUOs8Z9oB0r Ivi0rX3sH0dzyG5W57V/AgCsjz0+NSir1qvXuoX96SzyzfJYpD0z2iwNkUXxa6d9rXpN te5em0/EpPWv1qS/JuArwp/lwzl+f7iPEN2T0JxnrWc089nCVhW1hH1XKt/dHlH8myN/ 9dvA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :feedback-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=7jlcVHL9xXutHyudxpWgmNyuiG9QsSh1Xo0dK9zsWjA=; b=cD7lJj05Bv18AauPFM88JR2s0j7oQqCzxKxb5yv6iUIzn2ERqct72jpDUbbkxDkB7F ksJDsNr1x5Jf0Zc/fIpMQbjrHYkc5MevozqpzRIICMU07kdlDIQgHytAbRA++l27x00f idsVnM+Qz22iEktEANNbkFl+tdoop5bl+vPoTAttqxUW4u4Pw3ap1HTR9OsGZIyR6Dk5 UCtJi2BcGhlPksmmFFx9MQfznfLmuP9Z2+AU9E7vHLSk/bpUlJJKnAksmd9BLdpbo2Tj anqgYDWaxMbUBrCmW/Tf5eHLa5eSwqOO/vP/RkM/5Q9zx9jVbhEfkXVGBipDpd4PdVR3 pvYg== X-Gm-Message-State: ANoB5pn5usH0W/izC8ZzhJw3sN4Rc4BVnj6mQzHyq8PL8wy3xxzYfVsT /qORriHKKBR2wuILeGxE9Xk= X-Google-Smtp-Source: AA0mqf6IDL2RWE/H33qWuzB+/OwKdtxvd/iJIOwpxmlKGEm/zYT9LD2OYB9TH2WQWzdbh2CSWom+dA== X-Received: by 2002:a37:f516:0:b0:6fa:32ca:4944 with SMTP id l22-20020a37f516000000b006fa32ca4944mr52045610qkk.738.1669742604409; Tue, 29 Nov 2022 09:23:24 -0800 (PST) Received: from auth1-smtp.messagingengine.com (auth1-smtp.messagingengine.com. [66.111.4.227]) by smtp.gmail.com with ESMTPSA id t20-20020a05620a451400b006fba0a389a4sm11185702qkp.88.2022.11.29.09.23.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Nov 2022 09:23:23 -0800 (PST) Received: from compute4.internal (compute4.nyi.internal [10.202.2.44]) by mailauth.nyi.internal (Postfix) with ESMTP id 224C727C0054; Tue, 29 Nov 2022 12:23:22 -0500 (EST) Received: from mailfrontend1 ([10.202.2.162]) by compute4.internal (MEProxy); Tue, 29 Nov 2022 12:23:23 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvhedrtddtgdejudcutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpeffhffvvefukfhfgggtugfgjgesthekredttddtudenucfhrhhomhepuehoqhhu nhcuhfgvnhhguceosghoqhhunhdrfhgvnhhgsehgmhgrihhlrdgtohhmqeenucggtffrrg htthgvrhhnpeevuedtteetledvhfdtudekfffggeelhfejlefhgffgfedviefhgeeifeel vddtgeenucffohhmrghinheplhhkmhhlrdhorhhgpdhqvghmuhdrohhrghenucevlhhush htvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpegsohhquhhnodhmvghs mhhtphgruhhthhhpvghrshhonhgrlhhithihqdeiledvgeehtdeigedqudejjeekheehhe dvqdgsohhquhhnrdhfvghngheppehgmhgrihhlrdgtohhmsehfihigmhgvrdhnrghmvg X-ME-Proxy: Feedback-ID: iad51458e:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Tue, 29 Nov 2022 12:23:21 -0500 (EST) Date: Tue, 29 Nov 2022 09:23:18 -0800 From: Boqun Feng To: Waiman Long Cc: Hou Tao , Tonghao Zhang , Peter Zijlstra , Ingo Molnar , Will Deacon , netdev@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Jiri Olsa , bpf , Hao Luo , "houtao1@huawei.com" , LKML Subject: Re: [net-next] bpf: avoid hashtab deadlock with try_lock Message-ID: References: <9278cf3f-dfb6-78eb-8862-553545dac7ed@huawei.com> <41eda0ea-0ed4-1ffb-5520-06fda08e5d38@huawei.com> <07a7491e-f391-a9b2-047e-cab5f23decc5@huawei.com> <59fc54b7-c276-2918-6741-804634337881@huaweicloud.com> <541aa740-dcf3-35f5-9f9b-e411978eaa06@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <541aa740-dcf3-35f5-9f9b-e411978eaa06@redhat.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Nov 29, 2022 at 11:06:51AM -0500, Waiman Long wrote: > On 11/29/22 07:45, Hou Tao wrote: > > Hi, > > > > On 11/29/2022 2:06 PM, Tonghao Zhang wrote: > > > On Tue, Nov 29, 2022 at 12:32 PM Hou Tao wrote: > > > > Hi, > > > > > > > > On 11/29/2022 5:55 AM, Hao Luo wrote: > > > > > On Sun, Nov 27, 2022 at 7:15 PM Tonghao Zhang wrote: > > > > > Hi Tonghao, > > > > > > > > > > With a quick look at the htab_lock_bucket() and your problem > > > > > statement, I agree with Hou Tao that using hash & > > > > > min(HASHTAB_MAP_LOCK_MASK, n_bucket - 1) to index in map_locked seems > > > > > to fix the potential deadlock. Can you actually send your changes as > > > > > v2 so we can take a look and better help you? Also, can you explain > > > > > your solution in your commit message? Right now, your commit message > > > > > has only a problem statement and is not very clear. Please include > > > > > more details on what you do to fix the issue. > > > > > > > > > > Hao > > > > It would be better if the test case below can be rewritten as a bpf selftests. > > > > Please see comments below on how to improve it and reproduce the deadlock. > > > > > > Hi > > > > > > only a warning from lockdep. > > > > Thanks for your details instruction. I can reproduce the warning by using your > > > > setup. I am not a lockdep expert, it seems that fixing such warning needs to set > > > > different lockdep class to the different bucket. Because we use map_locked to > > > > protect the acquisition of bucket lock, so I think we can define lock_class_key > > > > array in bpf_htab (e.g., lockdep_key[HASHTAB_MAP_LOCK_COUNT]) and initialize the > > > > bucket lock accordingly. > > The proposed lockdep solution doesn't work. Still got lockdep warning after > > that, so cc +locking expert +lkml.org for lockdep help. > > > > Hi lockdep experts, > > > > We are trying to fix the following lockdep warning from bpf subsystem: > > > > [   36.092222] ================================ > > [   36.092230] WARNING: inconsistent lock state > > [   36.092234] 6.1.0-rc5+ #81 Tainted: G            E > > [   36.092236] -------------------------------- > > [   36.092237] inconsistent {INITIAL USE} -> {IN-NMI} usage. > > [   36.092238] perf/1515 [HC1[1]:SC0[0]:HE0:SE1] takes: > > [   36.092242] ffff888341acd1a0 (&htab->lockdep_key){....}-{2:2}, at: > > htab_lock_bucket+0x4d/0x58 > > [   36.092253] {INITIAL USE} state was registered at: > > [   36.092255]   mark_usage+0x1d/0x11d > > [   36.092262]   __lock_acquire+0x3c9/0x6ed > > [   36.092266]   lock_acquire+0x23d/0x29a > > [   36.092270]   _raw_spin_lock_irqsave+0x43/0x7f > > [   36.092274]   htab_lock_bucket+0x4d/0x58 > > [   36.092276]   htab_map_delete_elem+0x82/0xfb > > [   36.092278]   map_delete_elem+0x156/0x1ac > > [   36.092282]   __sys_bpf+0x138/0xb71 > > [   36.092285]   __do_sys_bpf+0xd/0x15 > > [   36.092288]   do_syscall_64+0x6d/0x84 > > [   36.092291]   entry_SYSCALL_64_after_hwframe+0x63/0xcd > > [   36.092295] irq event stamp: 120346 > > [   36.092296] hardirqs last  enabled at (120345): [] > > _raw_spin_unlock_irq+0x24/0x39 > > [   36.092299] hardirqs last disabled at (120346): [] > > generic_exec_single+0x40/0xb9 > > [   36.092303] softirqs last  enabled at (120268): [] > > __do_softirq+0x347/0x387 > > [   36.092307] softirqs last disabled at (120133): [] > > __irq_exit_rcu+0x67/0xc6 > > [   36.092311] > > [   36.092311] other info that might help us debug this: > > [   36.092312]  Possible unsafe locking scenario: > > [   36.092312] > > [   36.092313]        CPU0 > > [   36.092313]        ---- > > [   36.092314]   lock(&htab->lockdep_key); > > [   36.092315]   > > [   36.092316]     lock(&htab->lockdep_key); > > [   36.092318] > > [   36.092318]  *** DEADLOCK *** > > [   36.092318] > > [   36.092318] 3 locks held by perf/1515: > > [   36.092320]  #0: ffff8881b9805cc0 (&cpuctx_mutex){+.+.}-{4:4}, at: > > perf_event_ctx_lock_nested+0x8e/0xba > > [   36.092327]  #1: ffff8881075ecc20 (&event->child_mutex){+.+.}-{4:4}, at: > > perf_event_for_each_child+0x35/0x76 > > [   36.092332]  #2: ffff8881b9805c20 (&cpuctx_lock){-.-.}-{2:2}, at: > > perf_ctx_lock+0x12/0x27 > > [   36.092339] > > [   36.092339] stack backtrace: > > [   36.092341] CPU: 0 PID: 1515 Comm: perf Tainted: G            E > > 6.1.0-rc5+ #81 > > [   36.092344] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > > rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 > > [   36.092349] Call Trace: > > [   36.092351]  > > [   36.092354]  dump_stack_lvl+0x57/0x81 > > [   36.092359]  lock_acquire+0x1f4/0x29a > > [   36.092363]  ? handle_pmi_common+0x13f/0x1f0 > > [   36.092366]  ? htab_lock_bucket+0x4d/0x58 > > [   36.092371]  _raw_spin_lock_irqsave+0x43/0x7f > > [   36.092374]  ? htab_lock_bucket+0x4d/0x58 > > [   36.092377]  htab_lock_bucket+0x4d/0x58 > > [   36.092379]  htab_map_update_elem+0x11e/0x220 > > [   36.092386]  bpf_prog_f3a535ca81a8128a_bpf_prog2+0x3e/0x42 > > [   36.092392]  trace_call_bpf+0x177/0x215 > > [   36.092398]  perf_trace_run_bpf_submit+0x52/0xaa > > [   36.092403]  ? x86_pmu_stop+0x97/0x97 > > [   36.092407]  perf_trace_nmi_handler+0xb7/0xe0 > > [   36.092415]  nmi_handle+0x116/0x254 > > [   36.092418]  ? x86_pmu_stop+0x97/0x97 > > [   36.092423]  default_do_nmi+0x3d/0xf6 > > [   36.092428]  exc_nmi+0xa1/0x109 > > [   36.092432]  end_repeat_nmi+0x16/0x67 > > [   36.092436] RIP: 0010:wrmsrl+0xd/0x1b > > So the lock is really taken in a NMI context. In general, we advise again > using lock in a NMI context unless it is a lock that is used only in that > context. Otherwise, deadlock is certainly a possibility as there is no way > to mask off again NMI. > I think here they use a percpu counter as an "outer lock" to make the accesses to the real lock exclusive: preempt_disable(); a = __this_cpu_inc(->map_locked); if (a != 1) { __this_cpu_dec(->map_locked); preempt_enable(); return -EBUSY; } preempt_enable(); return -EBUSY; raw_spin_lock_irqsave(->raw_lock); and lockdep is not aware that ->map_locked acts as a lock. However, I feel this may be just a reinvented try_lock pattern, Hou Tao, could you see if this can be refactored with a try_lock? Otherwise, you may need to introduce a virtual lockclass for ->map_locked. Regards, Boqun > Cheers, > Longman >