From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-lj1-f173.google.com (mail-lj1-f173.google.com [209.85.208.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 152A32AF1E; Tue, 25 Feb 2025 17:41:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.208.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740505288; cv=none; b=EON2J1jIlTVD6Ygbvi+wBmRgfm1lKhJsmIr751TbDeZzavO89pwBwVqMa6z/IN6bxeimlfbopgu2uDUKiWk2nxwIB+zrm+TYHh6ALGMc1tatEUyoCuVTUyKmWfdtQZAYMmWDL8bNTV86G8qfUO9tjpuJJNpliR2eGKuSgQiBLL0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740505288; c=relaxed/simple; bh=zwNwtLOGPEbKxEDJG3ir/jA0Zv73WpvXFOn5sEteQQU=; h=From:Date:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=SP8m1orOtSIytI5yHdlkpsc3A1SXseIhzWjoDR3qzboaU8tsVwd+l/okV0yuPUD/fI+PTd2Mmk6DThlzXMb6333agfVlm+p32UJgCdlGgj6bsYv/LgEEnoE+s0RdbPemVoQ/expCDjCmxR3UXFJS4O2xH6wVp+OoohleLkTQPtc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=acv71CTl; arc=none smtp.client-ip=209.85.208.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="acv71CTl" Received: by mail-lj1-f173.google.com with SMTP id 38308e7fff4ca-30738a717ffso46151831fa.0; Tue, 25 Feb 2025 09:41:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1740505284; x=1741110084; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:from:to:cc:subject:date:message-id:reply-to; bh=o5I0Gh7oHoYbf3JrUTgHAlRAt4Em/lhq6oj6z2kkeWE=; b=acv71CTlK7DXHfP/BmY+AfX3QtO5JizDDmrxjPU2zV5/cjnZ5j/MEs0c0s/qlpYeEF dO+62+wLoBT6o9RZkR3QJC4gXQ6L0iqnI0TJ4HM5TZaxexMAGxDom7oiZ9ubT1IA8L5B T7igGnQr8RCG8g1Yygcp5nbAzjmjoZqG2t+5uRu8V2z0lbqaxvC71Cat3Xp43K97fKFV +8T0F5sPCr6WI5QUX7xrX5K3zvgNl/J2ZtOpgFDpWGQEaw977Zedn8mKBA5K3pirezGi 5kq0byV/W4wUR3vlXfW8ZfxBNRTijuXFNvYzFo+jWDIMjLK4GXQlaXS9AyQiLRNZBoh/ PwjQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740505284; x=1741110084; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:date:from:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=o5I0Gh7oHoYbf3JrUTgHAlRAt4Em/lhq6oj6z2kkeWE=; b=P72EZSwpp247qsmupRifmTiFoA+rdgt4EUZEYpfxZvyb9zriejklxd85UqmFy9p3sQ Ae6WkyRb03I7w5IKU/rBWllnYhk3SgRWu99WaIws0lBaQ8nUFcj2romdt2WaODqDIeCv vFBdKoGJaCPKtrGEyBjXMYwj8sY7wjuPb60pHtZNOVcYH9veZXwQR92ujS1uLHNHq2Pt lqw+Fruo4uerUXX6+RYsyhn2qUYPBrq95ZYy2byQbTuqScKkO/77NmnNc4iAM5zLvYIQ j3HnoH+dOQ0LHNbEl8ne5eNsRZ+t9DD6+wge4cmAAzp4YNJKKhDde9qcOjv5MI934POi 34fA== X-Forwarded-Encrypted: i=1; AJvYcCW5Kc7x/0nPXwWo1/43+SiAsxubkDQYV2pSxJJl9FVK6IKeg+znnfJzbqNaNEq3x8XyJ2iUixSrYi+qtoo=@vger.kernel.org, AJvYcCXHIAZfg1enouuoJPbNN6fuE6h5IUyQnRUiOFMF2InRX2+P8tt4ySUyJDQpIGgTXrBEFAst@vger.kernel.org X-Gm-Message-State: AOJu0YyGFxHHXf+QYm2TpKHQ8LQ57eYj2M0duXGIZ2Z4lW47b5gbsVDq gHjJQ93jhZ6E1pFtr6HXIWv9Z+b2Hsk6MsojdJzfHwAiIm6dnPZQsoM2xH/B X-Gm-Gg: ASbGnctZjNwY7FgbNPj5JaQ8+kYPfdNNvT+Xj0LedfXObtsHcy5jQyuiEC3Xf1tRapB 1NmIICifjFD8b35kbFXXikdG0bxZKg/5xrCAIYWUBKYKNW7skoraTqCPLEt2kD06xTam/bpq7B4 mz0/3AF2fCoSjdDrjv3SZbrNUWIKSHzLaCi4XpdcNeC4M2iZoXzHX45ZVNwK1Net50fBbt5p5K/ LSlTwiRTPbth6jJCgBm5sjKHvFOB8ZIQz5MXA/hkpGTuC73c36WGSbD+beodA1SVbDYy28gBfs/ JSpXK3B8RcHU3Uypg4q0ZJ+4WMRvXzggMJiA4PnTtBJTmdbC X-Google-Smtp-Source: AGHT+IERP4ZmgyXaES6UzO4zr1+NRzgRjYLzr48ZZE9JhLwNo3qlzKZThk4M0ZROHzByK2v+768Rzg== X-Received: by 2002:a2e:8642:0:b0:307:e302:a34 with SMTP id 38308e7fff4ca-30a598f6edemr66652541fa.20.1740505283628; Tue, 25 Feb 2025 09:41:23 -0800 (PST) Received: from pc636 (host-95-203-6-24.mobileonline.telia.com. [95.203.6.24]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-30a819f5e4asm2812131fa.63.2025.02.25.09.41.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Feb 2025 09:41:22 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 25 Feb 2025 18:41:19 +0100 To: Keith Busch , Vlastimil Babka Cc: Vlastimil Babka , Uladzislau Rezki , "Paul E. McKenney" , Joel Fernandes , Josh Triplett , Boqun Feng , Christoph Lameter , David Rientjes , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Julia Lawall , Jakub Kicinski , "Jason A. Donenfeld" , Andrew Morton , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, Alexander Potapenko , Marco Elver , Dmitry Vyukov , kasan-dev@googlegroups.com, Jann Horn , Mateusz Guzik , linux-nvme@lists.infradead.org, leitao@debian.org Subject: Re: [PATCH v2 6/7] mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy() Message-ID: References: <20240807-b4-slab-kfree_rcu-destroy-v2-0-ea79102f428c@suse.cz> <20240807-b4-slab-kfree_rcu-destroy-v2-6-ea79102f428c@suse.cz> <2811463a-751f-4443-9125-02628dc315d9@suse.cz> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Feb 25, 2025 at 10:05:37AM -0700, Keith Busch wrote: > On Tue, Feb 25, 2025 at 09:03:38AM -0700, Keith Busch wrote: > > On Tue, Feb 25, 2025 at 10:57:38AM +0100, Vlastimil Babka wrote: > > > I tried to create a kunit test for it, but it doesn't trigger anything. Maybe > > > it's too simple, or racy, and thus we are not flushing any of the queues from > > > kvfree_rcu_barrier()? > > > > Thanks, your test readily triggers it for me, but only if I load > > rcutorture at the same time. > > Oops, I sent the wrong kernel messages. This is the relevant part: > > [ 142.371052] workqueue: WQ_MEM_RECLAIM > test_kfree_rcu_destroy_wq:cache_destroy_workfn [slub_kunit] is > flushing !WQ_MEM_RECLAIM events_unbound:kfree_rcu_work > [ 142.371072] WARNING: CPU: 11 PID: 186 at kernel/workqueue.c:3715 > check_flush_dependency.part.0+0xad/0x100 > [ 142.375748] Modules linked in: slub_kunit(E) rcutorture(E) > torture(E) kunit(E) iTCO_wdt(E) iTCO_vendor_support(E) > intel_uncore_frequency_common(E) skx_edac_common(E) nfit(E) > libnvdimm(E) kvm_intel(E) kvm(E) evdev(E) bochs(E) serio_raw(E) > drm_kms_helper(E) i2c_i801(E) e1000e(E) i2c_smbus(E) intel_agp(E) > intel_gtt(E) lpc_ich(E) agpgart(E) mfd_core(E) drm_shm] > [ 142.384553] CPU: 11 UID: 0 PID: 186 Comm: kworker/u64:11 Tainted: G > E N 6.13.0-04839-g5e7b40f0ddce-dirty #831 > [ 142.386755] Tainted: [E]=UNSIGNED_MODULE, [N]=TEST > [ 142.387849] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), > BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 > [ 142.390236] Workqueue: test_kfree_rcu_destroy_wq > cache_destroy_workfn [slub_kunit] > [ 142.391863] RIP: 0010:check_flush_dependency.part.0+0xad/0x100 > [ 142.393183] Code: 75 dc 48 8b 55 18 49 8d 8d 78 01 00 00 4d 89 f0 > 48 81 c6 78 01 00 00 48 c7 c7 00 e1 9a 82 c6 05 4f 39 c5 02 01 e8 53 > bd fd ff <0f> 0b 5b 5d 41 5c 41 5d 41 5e c3 80 3d 39 39 c5 02 00 75 83 > 41 8b > [ 142.396981] RSP: 0018:ffffc900007cfc90 EFLAGS: 00010092 > [ 142.398124] RAX: 000000000000008f RBX: ffff88803e9b10a0 RCX: 0000000000000027 > [ 142.399605] RDX: ffff88803eba0d08 RSI: 0000000000000001 RDI: ffff88803eba0d00 > [ 142.401092] RBP: ffff888007d9a480 R08: ffffffff83b8c808 R09: 0000000000000003 > [ 142.402548] R10: ffffffff8348c820 R11: ffffffff83a11d58 R12: ffff888007150000 > [ 142.404098] R13: ffff888005961400 R14: ffffffff813221a0 R15: ffff888005961400 > [ 142.405561] FS: 0000000000000000(0000) GS:ffff88803eb80000(0000) > knlGS:0000000000000000 > [ 142.407297] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 142.408658] CR2: 00007f826bd1a000 CR3: 00000000069db002 CR4: 0000000000772ef0 > [ 142.410259] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 142.411871] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 142.413341] PKRU: 55555554 > [ 142.414038] Call Trace: > [ 142.414658] > [ 142.415249] ? __warn+0x8d/0x180 > [ 142.416035] ? check_flush_dependency.part.0+0xad/0x100 > [ 142.417182] ? report_bug+0x160/0x170 > [ 142.418041] ? handle_bug+0x4f/0x90 > [ 142.418861] ? exc_invalid_op+0x14/0x70 > [ 142.419853] ? asm_exc_invalid_op+0x16/0x20 > [ 142.420877] ? kfree_rcu_shrink_scan+0x120/0x120 > [ 142.422029] ? check_flush_dependency.part.0+0xad/0x100 > [ 142.423244] __flush_work+0x38a/0x4a0 > [ 142.424157] ? find_held_lock+0x2b/0x80 > [ 142.425070] ? flush_rcu_work+0x26/0x40 > [ 142.425953] ? lock_release+0xb3/0x250 > [ 142.426785] ? __mutex_unlock_slowpath+0x2c/0x270 > [ 142.427906] flush_rcu_work+0x30/0x40 > [ 142.428756] kvfree_rcu_barrier+0xe9/0x130 > [ 142.429649] kmem_cache_destroy+0x2b/0x1f0 > [ 142.430578] cache_destroy_workfn+0x20/0x40 [slub_kunit] > [ 142.431729] process_one_work+0x1cd/0x560 > [ 142.432620] worker_thread+0x183/0x310 > [ 142.433487] ? rescuer_thread+0x330/0x330 > [ 142.434428] kthread+0xd8/0x1d0 > [ 142.435248] ? ret_from_fork+0x17/0x50 > [ 142.436165] ? lock_release+0xb3/0x250 > [ 142.437106] ? kthreads_online_cpu+0xf0/0xf0 > [ 142.438133] ret_from_fork+0x2d/0x50 > [ 142.439045] ? kthreads_online_cpu+0xf0/0xf0 > [ 142.440428] ret_from_fork_asm+0x11/0x20 > [ 142.441476] > [ 142.442152] irq event stamp: 22858 > [ 142.443002] hardirqs last enabled at (22857): [] > _raw_spin_unlock_irq+0x24/0x30 > [ 142.445032] hardirqs last disabled at (22858): [] > _raw_spin_lock_irq+0x43/0x50 > [ 142.451450] softirqs last enabled at (22714): [] > __irq_exit_rcu+0xac/0xd0 > [ 142.453345] softirqs last disabled at (22709): [] > __irq_exit_rcu+0xac/0xd0 > [ 142.455305] ---[ end trace 0000000000000000 ]--- Thanks! I can trigger this also: [ 21.712856] KTAP version 1 [ 21.712862] 1..1 [ 21.714486] KTAP version 1 [ 21.714490] # Subtest: slub_test [ 21.714492] # module: slub_kunit [ 21.714495] 1..10 [ 21.750359] ok 1 test_clobber_zone [ 21.750955] ok 2 test_next_pointer [ 21.751532] ok 3 test_first_word [ 21.751991] ok 4 test_clobber_50th_byte [ 21.752493] ok 5 test_clobber_redzone_free [ 21.753004] stackdepot: allocating hash table of 1048576 entries via kvcalloc [ 21.756176] ok 6 test_kmalloc_redzone_access [ 21.806549] ok 7 test_kfree_rcu [ 22.058010] ------------[ cut here ]------------ [ 22.058015] workqueue: WQ_MEM_RECLAIM test_kfree_rcu_destroy_wq:cache_destroy_workfn [slub_kunit] is flushing !WQ_MEM_RECLAIM events_unbound:kfree_rcu_work [ 22.058039] WARNING: CPU: 19 PID: 474 at kernel/workqueue.c:3715 check_flush_dependency.part.0+0xbe/0x130 [ 22.058047] Modules linked in: slub_kunit(E) kunit(E) binfmt_misc(E) bochs(E) drm_client_lib(E) drm_shmem_helper(E) ppdev(E) drm_kms_helper(E) snd_pcm(E) sg(E) snd_timer(E) evdev(E) snd(E) joydev(E) parport_pc(E) parport(E) soundcore(E) serio_raw(E) button(E) pcspkr(E) drm(E) fuse(E) dm_mod(E) efi_pstore(E) configfs(E) loop(E) qemu_fw_cfg(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) sr_mod(E) sd_mod(E) cdrom(E) ata_generic(E) ata_piix(E) libata(E) scsi_mod(E) i2c_piix4(E) psmouse(E) e1000(E) i2c_smbus(E) scsi_common(E) floppy(E) [ 22.058091] CPU: 19 UID: 0 PID: 474 Comm: kworker/u257:0 Kdump: loaded Tainted: G E N 6.14.0-rc1+ #286 [ 22.058096] Tainted: [E]=UNSIGNED_MODULE, [N]=TEST [ 22.058097] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 [ 22.058099] Workqueue: test_kfree_rcu_destroy_wq cache_destroy_workfn [slub_kunit] [ 22.058103] RIP: 0010:check_flush_dependency.part.0+0xbe/0x130 [ 22.058106] Code: 75 d0 48 8b 55 18 49 8d 8d c0 00 00 00 4d 89 f0 48 81 c6 c0 00 00 00 48 c7 c7 b0 7d c8 bd c6 05 6c 78 53 01 01 e8 a2 ae fd ff <0f> 0b 5b 5d 41 5c 41 5d 41 5e c3 cc cc cc cc f6 c4 08 74 94 31 ed [ 22.058108] RSP: 0018:ffff95e5c123fd50 EFLAGS: 00010086 [ 22.058111] RAX: 0000000000000000 RBX: ffff89a4ff22d5a0 RCX: 0000000000000000 [ 22.058113] RDX: 0000000000000003 RSI: ffffffffbdce1697 RDI: 00000000ffffffff [ 22.058114] RBP: ffff89961043a780 R08: 0000000000000000 R09: 0000000000000003 [ 22.058116] R10: ffff95e5c123fbe8 R11: ffff89a53fefefa8 R12: ffff89960cb6b080 [ 22.058117] R13: ffff899600051400 R14: ffffffffbcf2ba80 R15: ffff89960005a800 [ 22.058120] FS: 0000000000000000(0000) GS:ffff89a4ff2c0000(0000) knlGS:0000000000000000 [ 22.058122] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 22.058124] CR2: 000055bf2cbc6038 CR3: 000000010dc1e000 CR4: 00000000000006f0 [ 22.058128] Call Trace: [ 22.058130] [ 22.058133] ? __warn+0x85/0x130 [ 22.058137] ? check_flush_dependency.part.0+0xbe/0x130 [ 22.058139] ? report_bug+0x18d/0x1c0 [ 22.058142] ? prb_read_valid+0x17/0x20 [ 22.058147] ? handle_bug+0x58/0x90 [ 22.058151] ? exc_invalid_op+0x13/0x60 [ 22.058154] ? asm_exc_invalid_op+0x16/0x20 [ 22.058158] ? __pfx_kfree_rcu_work+0x10/0x10 [ 22.058162] ? check_flush_dependency.part.0+0xbe/0x130 [ 22.058165] __flush_work+0xd6/0x320 [ 22.058168] flush_rcu_work+0x39/0x50 [ 22.058171] kvfree_rcu_barrier+0xe9/0x130 [ 22.058174] kmem_cache_destroy+0x18/0x140 [ 22.058177] process_one_work+0x184/0x3a0 [ 22.058180] worker_thread+0x24d/0x360 [ 22.058183] ? __pfx_worker_thread+0x10/0x10 [ 22.058185] kthread+0xfc/0x230 [ 22.058189] ? finish_task_switch.isra.0+0x85/0x2a0 [ 22.058192] ? __pfx_kthread+0x10/0x10 [ 22.058195] ret_from_fork+0x30/0x50 [ 22.058199] ? __pfx_kthread+0x10/0x10 [ 22.058202] ret_from_fork_asm+0x1a/0x30 [ 22.058206] [ 22.058207] ---[ end trace 0000000000000000 ]--- [ 23.123507] ok 8 test_kfree_rcu_wq_destroy [ 23.151033] ok 9 test_leak_destroy [ 23.151612] ok 10 test_krealloc_redzone_zeroing [ 23.151617] # slub_test: pass:10 fail:0 skip:0 total:10 [ 23.151619] # Totals: pass:10 fail:0 skip:0 total:10 [ 23.151620] ok 1 slub_test urezki@pc638:~$ but i had to adapt slightly the Vlastimil's test: diff --git a/lib/slub_kunit.c b/lib/slub_kunit.c index f11691315c2f..222f6d204b0d 100644 --- a/lib/slub_kunit.c +++ b/lib/slub_kunit.c @@ -6,6 +6,7 @@ #include #include #include +#include #include "../mm/slab.h" static struct kunit_resource resource; @@ -181,6 +182,63 @@ static void test_kfree_rcu(struct kunit *test) KUNIT_EXPECT_EQ(test, 0, slab_errors); } +struct cache_destroy_work { + struct work_struct work; + struct kmem_cache *s; +}; + +static void cache_destroy_workfn(struct work_struct *w) +{ + struct cache_destroy_work *cdw; + + cdw = container_of(w, struct cache_destroy_work, work); + kmem_cache_destroy(cdw->s); +} + +#define KMEM_CACHE_DESTROY_NR 10 + +static void test_kfree_rcu_wq_destroy(struct kunit *test) +{ + struct test_kfree_rcu_struct *p; + struct cache_destroy_work cdw; + struct workqueue_struct *wq; + struct kmem_cache *s; + unsigned int rnd; + int i; + + if (IS_BUILTIN(CONFIG_SLUB_KUNIT_TEST)) + kunit_skip(test, "can't do kfree_rcu() when test is built-in"); + + INIT_WORK_ONSTACK(&cdw.work, cache_destroy_workfn); + wq = alloc_workqueue("test_kfree_rcu_destroy_wq", + WQ_HIGHPRI | WQ_UNBOUND | WQ_MEM_RECLAIM, 0); + + if (!wq) + kunit_skip(test, "failed to alloc wq"); + + for (i = 0; i < KMEM_CACHE_DESTROY_NR; i++) { + s = test_kmem_cache_create("TestSlub_kfree_rcu_wq_destroy", + sizeof(struct test_kfree_rcu_struct), + SLAB_NO_MERGE); + + if (!s) + kunit_skip(test, "failed to create cache"); + + rnd = get_random_u8() % 255; + p = kmem_cache_alloc(s, GFP_KERNEL); + kfree_rcu(p, rcu); + + cdw.s = s; + + msleep(rnd); + queue_work(wq, &cdw.work); + flush_work(&cdw.work); + } + + destroy_workqueue(wq); + KUNIT_EXPECT_EQ(test, 0, slab_errors); +} + static void test_leak_destroy(struct kunit *test) { struct kmem_cache *s = test_kmem_cache_create("TestSlub_leak_destroy", @@ -254,6 +312,7 @@ static struct kunit_case test_cases[] = { KUNIT_CASE(test_clobber_redzone_free), KUNIT_CASE(test_kmalloc_redzone_access), KUNIT_CASE(test_kfree_rcu), + KUNIT_CASE(test_kfree_rcu_wq_destroy), KUNIT_CASE(test_leak_destroy), KUNIT_CASE(test_krealloc_redzone_zeroing), {} -- Uladzislau Rezki