From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 B972A27A907; Fri, 7 Aug 2026 06:45:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786085154; cv=none; b=Cz0U4MpIVS2BIumDGAPET95Uxo9UPE2Dal6CIjxnpnsmudmyC0pF7QvbrxiNGpjNjuaq03RA9pxDkc0OUbOVDixdUyC/gIapLyMsDiPehAvw5zWdZAXTlGKiK7bE/mlQzdjXbHQn4JG9QJMsNOYbWy4SBgsKbR/TzpoAxGcl01c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786085154; c=relaxed/simple; bh=84cyBJf8fSQ/v8PtTSYSpvHiZ8RN0Zd04fYbHTpxMhc=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=h/9n5Hx0bh68KIxzf1uwzTzo/z3dkDhdJu1PkCf7JYX2iZLFdHWOB7D4AmvMAAC3RqJnJHwsguaJeBllAB6zHkS+xyB/NoAERRQc3PHuVouKe+Na1ygMWw1jB2sqDi7UMUAXl5nRa2WNORil8GVcmL2fURQ4B2BJVO0K66V+A8E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=buRjjZUy; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="buRjjZUy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BBFD1F00A3A; Fri, 7 Aug 2026 06:45:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786085153; bh=GFp8IxywBCbWdweVabG/3grrD1nmpDk9rfvKiuf1E1w=; h=Date:Subject:To:References:From:In-Reply-To; b=buRjjZUy7afMVbBZcMrlhehQh27leSBNcFS0tCp80PVPqNW02H3WFLUQyrRD9i+3V qcIsBQecHufSvhjDpPuHO7v/rREhdsOzfBoJ+BpLMIzUYY/uMSr5kOM3BGYLymNbuu F6FKZufjXPHP0LFM5/UONMciIf57w1VZ3ITcQA709M8+RGmPU1BGYRWHOSUMRcuVjY 7H2EtiUqvaOq9V7TIZYBRiTkhb74np7M7w4+Iv6tWJNONouFV0dV0VkS/1T2Gl88eE NMrJmwZa41U04eiNKTJsvXXlSdCcFMlL6cTU7xQwX9jvsUtThTj53yk0t1h4Pcj0xG 6VFJuSLV5z/FA== Message-ID: Date: Fri, 7 Aug 2026 08:45:50 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [syzbot] [serial?] WARNING in register_console To: syzbot , gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, syzkaller-bugs@googlegroups.com References: <6a7411dd.9c11d2ce.289b96.0094.GAE@google.com> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06. 08. 26, 6:47, syzbot wrote: > syzbot has found a reproducer for the following issue on: > > HEAD commit: 0d8395707651 Merge tag 'soc-fixes-7.2-2' of git://git.kern.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=10883c99580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=cb17729fb04b1e3a > dashboard link: https://syzkaller.appspot.com/bug?extid=1ebbc20f223b99446034 > compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15b1bbb9580000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/14b35ca281d5/disk-0d839570.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/68c2ac2fdce0/vmlinux-0d839570.xz > kernel image: https://storage.googleapis.com/syzbot-assets/29bdd737b48f/bzImage-0d839570.xz > mounted in repro: https://storage.googleapis.com/syzbot-assets/cce97dbb2265/mount_0.gz > fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=11da8e49580000) > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+1ebbc20f223b99446034@syzkaller.appspotmail.com > > printk: legacy console [ttyS0] enabled > ------------[ cut here ]------------ > IS_ERR(kt) Well, the creation of "pr/legacy" thread failed. Would be nice to see what is actual PTR_ERR(kt). > WARNING: kernel/printk/printk.c:3728 at legacy_kthread_create kernel/printk/printk.c:3728 [inline], CPU#0: syz.4.49/6392 > WARNING: kernel/printk/printk.c:3728 at printk_kthreads_check_locked+0x2a7/0x3f0 kernel/printk/printk.c:3802, CPU#0: syz.4.49/6392 > Modules linked in: > CPU: 0 UID: 0 PID: 6392 Comm: syz.4.49 Not tainted syzkaller #0 PREEMPT_{RT,(full)} > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026 > RIP: 0010:legacy_kthread_create kernel/printk/printk.c:3728 [inline] > RIP: 0010:printk_kthreads_check_locked+0x2a7/0x3f0 kernel/printk/printk.c:3802 > Code: fe c1 38 c1 7c 9a 4c 89 f7 e8 c5 85 8a 00 eb 90 e8 7e 12 21 00 eb 05 e8 77 12 21 00 b0 01 88 05 2f a4 08 18 e9 e2 00 00 00 90 <0f> 0b 90 48 c7 c7 80 bd 6d 8b e8 1a 9f 82 ff 48 8b 1d 93 9e 04 18 > RSP: 0018:ffffc9000509fa70 EFLAGS: 00010206 > RAX: fffffffffffffffc RBX: 0000000000000001 RCX: 10959546c0351c00 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 > RBP: ffffc9000509fb70 R08: ffff888032eb2daf R09: 1ffff110065d65b5 > R10: dffffc0000000000 R11: ffffed10065d65b6 R12: 0000000000000000 > R13: dffffc0000000000 R14: 1ffff92000a13f5c R15: dffffc0000000000 > FS: 00007f7f4a99d6c0(0000) GS:ffff888125c3e000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fd99747f000 CR3: 000000003dd70000 CR4: 00000000003526f0 > Call Trace: > > register_console+0xc19/0xfc0 kernel/printk/printk.c:4221 > console_store+0x359/0x4f0 drivers/tty/serial/serial_core.c:2999 console_store() is serialized by a mutex. So this should not be a race. I cannot reproduce using: while :; do echo 0 >/sys/class/tty/ttyS0/console echo 1 > /sys/class/tty/ttyS0/console done That's what the reproducer suggests is the cause. thanks, -- js suse labs