From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7DA8825776 for ; Wed, 8 Apr 2026 23:52:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775692364; cv=none; b=a75mwoHoKFV7k5vgtQTR5ZwewpF+ihpcfI3dJneIqRDbxx/XHdCp/51rS08ADKaC3xP4w0UHFhjLXK/cjZqves02WYXyJpNANn7CEqAa78Ad0W1WA2k8wMgU/e8tFu0vsAbeao7lsy8FIUQ49lXmpUh0r/WxOoR3Y7LCb3qTV/0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775692364; c=relaxed/simple; bh=NoXTCDZdFrEUxD6kvr1g80kAzOx+axNA5Wxx5KjLhms=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=bCQJLt6St/QAyDVv72sGwtRDpiO1JhaX/pVr9CynviQmDt1BYLOBfTTzdex9PPRg3ReJwtpBexTvhKUQTVQh7toluK04hAAPtESfg+/N4kvvQZ40MkNVJa2wwZMddpQqEb9jm41dLpk2SMFCbdYnsvXWmpmDqmihH0fffq33/+U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=CvHUGpMI; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="CvHUGpMI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9BA50C19421; Wed, 8 Apr 2026 23:52:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1775692364; bh=NoXTCDZdFrEUxD6kvr1g80kAzOx+axNA5Wxx5KjLhms=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=CvHUGpMI8iV7a3qdD67rMlMQHJwIimrGieGk/w1PMg8Hj+buOG1fSH0hb3ppNkZM0 Y91A9xAB9FDcvJhqGNMDoTX1877jXPFf/w2DTEFWbZmySvnagFP0eVwy89t4JfR53r I89zcnym4lP3mR8G6REEGzbqHKREANmsHwjl5wu4= Date: Wed, 8 Apr 2026 16:52:42 -0700 From: Andrew Morton To: syzbot Cc: hannes@cmpxchg.org, jackmanb@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, surenb@google.com, syzkaller-bugs@googlegroups.com, vbabka@kernel.org, ziy@nvidia.com, Dmitry Vyukov , Andrey Konovalov , kasan-dev@googlegroups.com Subject: Re: [syzbot] [mm?] INFO: rcu detected stall in kcov_ioctl (3) Message-Id: <20260408165242.3cc507e32217426be2686a8e@linux-foundation.org> In-Reply-To: <69d6e54f.a00a0220.468cb.0012.GAE@google.com> References: <69d6e54f.a00a0220.468cb.0012.GAE@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit On Wed, 08 Apr 2026 16:31:27 -0700 syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 7ca6d1cfec80 Merge tag 'powerpc-7.0-4' of git://git.kernel.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=133b4dda580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=64e78d99d9bf8b4c > dashboard link: https://syzkaller.appspot.com/bug?extid=8a59070fc852219166ab > compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 > > Unfortunately, I don't have any reproducer for this issue yet. Thanks. I added a few kcov names from MAINTAINERS. > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/ace9641c44ac/disk-7ca6d1cf.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/6e66f8b9476e/vmlinux-7ca6d1cf.xz > kernel image: https://storage.googleapis.com/syzbot-assets/d679c066df56/bzImage-7ca6d1cf.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+8a59070fc852219166ab@syzkaller.appspotmail.com > > bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0) > rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: > rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P23414/1:b..l P27649/1:b..l P27664/1:b..l > rcu: (detected by 0, t=10502 jiffies, g=200461, q=440 ncpus=2) > task:syz-executor state:R running task stack:25416 pid:27664 tgid:27664 ppid:5809 task_flags:0x400000 flags:0x00080000 > Call Trace: > > context_switch kernel/sched/core.c:5298 [inline] > __schedule+0xfee/0x6120 kernel/sched/core.c:6911 > preempt_schedule_irq+0x50/0x90 kernel/sched/core.c:7238 > irqentry_exit+0x17b/0x670 kernel/entry/common.c:239 > asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697 > RIP: 0010:__orc_find+0x49/0xf0 arch/x86/kernel/unwind_orc.c:101 > Code: 00 49 89 fe 48 89 f0 49 39 fc 72 7b 48 b9 00 00 00 00 00 fc ff df 49 89 ff 48 89 fd eb 0c 48 8d 6b 04 49 89 df 49 39 ec 72 4e <4c> 89 e2 48 29 ea 48 89 d6 48 c1 ea 3f 48 c1 fe 02 48 01 f2 48 d1 > RSP: 0018:ffffc9000d12f138 EFLAGS: 00000212 > RAX: ffffffff91777f46 RBX: ffffffff90f165c4 RCX: dffffc0000000000 > RDX: ffffffff81aecd9f RSI: 0000000000000000 RDI: ffffffff90f165b8 > RBP: ffffffff90f165b8 R08: ffffffff91777f70 R09: 0000000000000007 > R10: 0000000000000200 R11: 000000000000aecd R12: ffffffff90f165c0 > R13: ffffffff81aecd22 R14: ffffffff90f165b8 R15: ffffffff90f165b8 > orc_find arch/x86/kernel/unwind_orc.c:238 [inline] > unwind_next_frame+0x2ec/0x1ea0 arch/x86/kernel/unwind_orc.c:510 > __unwind_start+0x3d1/0x7f0 arch/x86/kernel/unwind_orc.c:773 > unwind_start arch/x86/include/asm/unwind.h:64 [inline] > arch_stack_walk+0x73/0xf0 arch/x86/kernel/stacktrace.c:24 > stack_trace_save+0x8e/0xc0 kernel/stacktrace.c:122 > save_stack+0x162/0x1e0 mm/page_owner.c:165 > __set_page_owner+0x8c/0x540 mm/page_owner.c:341 > set_page_owner include/linux/page_owner.h:32 [inline] > post_alloc_hook+0x153/0x170 mm/page_alloc.c:1889 > prep_new_page mm/page_alloc.c:1897 [inline] > get_page_from_freelist+0x111d/0x3140 mm/page_alloc.c:3962 > __alloc_frozen_pages_noprof+0x27c/0x2ba0 mm/page_alloc.c:5250 > __alloc_pages_noprof mm/page_alloc.c:5284 [inline] > alloc_pages_bulk_noprof+0x782/0x1490 mm/page_alloc.c:5204 > ___alloc_pages_bulk mm/kasan/shadow.c:345 [inline] > __kasan_populate_vmalloc_do mm/kasan/shadow.c:370 [inline] > __kasan_populate_vmalloc+0xf0/0x210 mm/kasan/shadow.c:424 > kasan_populate_vmalloc include/linux/kasan.h:580 [inline] > alloc_vmap_area+0x95d/0x2bd0 mm/vmalloc.c:2129 > __get_vm_area_node+0x1ca/0x330 mm/vmalloc.c:3232 > __vmalloc_node_range_noprof+0x213/0x1530 mm/vmalloc.c:4024 > vmalloc_user_noprof+0x9e/0xe0 mm/vmalloc.c:4218 > kcov_ioctl+0x4c/0x720 kernel/kcov.c:726 > vfs_ioctl fs/ioctl.c:51 [inline] I assume the fuzzer is asking kcov_ioctl() to allocate ludicrous amounts of memory. case KCOV_INIT_TRACE: /* * Enable kcov in trace mode and setup buffer size. * Must happen before anything else. * * First check the size argument - it must be at least 2 * to hold the current position and one PC. */ size = arg; if (size < 2 || size > INT_MAX / sizeof(unsigned long)) return -EINVAL; area = vmalloc_user(size * sizeof(unsigned long)); KCOV_REMOTE_MAX_HANDLES looks to be OK. /sys/debug/kcov is mode 0600 so this is no emergency. Maintainers, perhaps we can do something more ... restrained here?