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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 920F4C433F5 for ; Wed, 11 May 2022 06:50:51 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 00AFB6B0073; Wed, 11 May 2022 02:50:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EFCFA8D0001; Wed, 11 May 2022 02:50:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DC5356B0078; Wed, 11 May 2022 02:50:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id CDF316B0073 for ; Wed, 11 May 2022 02:50:50 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 9F9603289F for ; Wed, 11 May 2022 06:50:50 +0000 (UTC) X-FDA: 79452539460.14.6A3FDFB Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf01.hostedemail.com (Postfix) with ESMTP id 625BC40003 for ; Wed, 11 May 2022 06:50:38 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 515C8617FB; Wed, 11 May 2022 06:50:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 55530C385DB; Wed, 11 May 2022 06:50:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1652251848; bh=EPtahW9l/Zi0zg2ZV5hZKf+m/NZbM7cRdmVPxgPKIEM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=warw4ZV9i+HysSVjSdhNrjzEae4jlsW9+PDmVi2v5/q3+ZItWy8I/CE71a2exbAnd DJZIaKkmWhmUIBby4O+XH/Qp5Mv1y+s2NOiPu4bgqvkzUeiYcUoQQKHVhL/V0KweLW lNO/mBZIdbh+pB+8ucK6ZjSCuxAxlkoHlwCy3sa8= Date: Wed, 11 May 2022 08:50:45 +0200 From: Greg KH To: Qi Zheng Cc: akpm@linux-foundation.org, jirislaby@kernel.org, akinobu.mita@gmail.com, vbabka@suse.cz, rostedt@goodmis.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 2/2] tty: fix deadlock caused by calling printk() under tty_port->lock Message-ID: References: <20220511061951.1114-1-zhengqi.arch@bytedance.com> <20220511061951.1114-2-zhengqi.arch@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220511061951.1114-2-zhengqi.arch@bytedance.com> X-Rspamd-Queue-Id: 625BC40003 X-Stat-Signature: yrgdwgz56wr9zu64g54p8iossiswcnkb Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=linuxfoundation.org header.s=korg header.b=warw4ZV9; dmarc=pass (policy=none) header.from=linuxfoundation.org; spf=pass (imf01.hostedemail.com: domain of gregkh@linuxfoundation.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1652251838-214514 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 11, 2022 at 02:19:51PM +0800, Qi Zheng wrote: > The pty_write() invokes kmalloc() which may invoke a normal printk() to > print failure message. This can cause a deadlock in the scenario reported > by syz-bot below: > > CPU0 CPU1 CPU2 > ---- ---- ---- > lock(console_owner); > lock(&port_lock_key); > lock(&port->lock); > lock(&port_lock_key); > lock(&port->lock); > lock(console_owner); > > As commit dbdda842fe96 ("printk: Add console owner and waiter logic to > load balance console writes") said, such deadlock can be prevented by > using printk_deferred() in kmalloc() (which is invoked in the section > guarded by the port->lock). But there are too many printk() on the > kmalloc() path, and kmalloc() can be called from anywhere, so changing > printk() to printk_deferred() is too complicated and inelegant. > > Therefore, this patch chooses to specify __GFP_NOWARN to kmalloc(), so > that printk() will not be called, and this deadlock problem can be avoided. > > Syz-bot reported the following lockdep error: > > ====================================================== > WARNING: possible circular locking dependency detected > 5.4.143-00237-g08ccc19a-dirty #10 Not tainted > ------------------------------------------------------ > syz-executor.4/29420 is trying to acquire lock: > ffffffff8aedb2a0 (console_owner){....}-{0:0}, at: console_trylock_spinning kernel/printk/printk.c:1752 [inline] > ffffffff8aedb2a0 (console_owner){....}-{0:0}, at: vprintk_emit+0x2ca/0x470 kernel/printk/printk.c:2023 > > but task is already holding lock: > ffff8880119c9158 (&port->lock){-.-.}-{2:2}, at: pty_write+0xf4/0x1f0 drivers/tty/pty.c:120 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #2 (&port->lock){-.-.}-{2:2}: > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] > _raw_spin_lock_irqsave+0x35/0x50 kernel/locking/spinlock.c:159 > tty_port_tty_get drivers/tty/tty_port.c:288 [inline] <-- lock(&port->lock); > tty_port_default_wakeup+0x1d/0xb0 drivers/tty/tty_port.c:47 > serial8250_tx_chars+0x530/0xa80 drivers/tty/serial/8250/8250_port.c:1767 > serial8250_handle_irq.part.0+0x31f/0x3d0 drivers/tty/serial/8250/8250_port.c:1854 > serial8250_handle_irq drivers/tty/serial/8250/8250_port.c:1827 [inline] <-- lock(&port_lock_key); > serial8250_default_handle_irq+0xb2/0x220 drivers/tty/serial/8250/8250_port.c:1870 > serial8250_interrupt+0xfd/0x200 drivers/tty/serial/8250/8250_core.c:126 > __handle_irq_event_percpu+0x109/0xa50 kernel/irq/handle.c:156 > [...] > > -> #1 (&port_lock_key){-.-.}-{2:2}: > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] > _raw_spin_lock_irqsave+0x35/0x50 kernel/locking/spinlock.c:159 > serial8250_console_write+0x184/0xa40 drivers/tty/serial/8250/8250_port.c:3198 > <-- lock(&port_lock_key); > call_console_drivers kernel/printk/printk.c:1819 [inline] > console_unlock+0x8cb/0xd00 kernel/printk/printk.c:2504 > vprintk_emit+0x1b5/0x470 kernel/printk/printk.c:2024 <-- lock(console_owner); > vprintk_func+0x8d/0x250 kernel/printk/printk_safe.c:394 > printk+0xba/0xed kernel/printk/printk.c:2084 > register_console+0x8b3/0xc10 kernel/printk/printk.c:2829 > univ8250_console_init+0x3a/0x46 drivers/tty/serial/8250/8250_core.c:681 > console_init+0x49d/0x6d3 kernel/printk/printk.c:2915 > start_kernel+0x5e9/0x879 init/main.c:713 > secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241 > > -> #0 (console_owner){....}-{0:0}: > [...] > lock_acquire+0x127/0x340 kernel/locking/lockdep.c:4734 > console_trylock_spinning kernel/printk/printk.c:1773 [inline] <-- lock(console_owner); > vprintk_emit+0x307/0x470 kernel/printk/printk.c:2023 > vprintk_func+0x8d/0x250 kernel/printk/printk_safe.c:394 > printk+0xba/0xed kernel/printk/printk.c:2084 > fail_dump lib/fault-inject.c:45 [inline] > should_fail+0x67b/0x7c0 lib/fault-inject.c:144 > __should_failslab+0x152/0x1c0 mm/failslab.c:33 > should_failslab+0x5/0x10 mm/slab_common.c:1224 > slab_pre_alloc_hook mm/slab.h:468 [inline] > slab_alloc_node mm/slub.c:2723 [inline] > slab_alloc mm/slub.c:2807 [inline] > __kmalloc+0x72/0x300 mm/slub.c:3871 > kmalloc include/linux/slab.h:582 [inline] > tty_buffer_alloc+0x23f/0x2a0 drivers/tty/tty_buffer.c:175 > __tty_buffer_request_room+0x156/0x2a0 drivers/tty/tty_buffer.c:273 > tty_insert_flip_string_fixed_flag+0x93/0x250 drivers/tty/tty_buffer.c:318 > tty_insert_flip_string include/linux/tty_flip.h:37 [inline] > pty_write+0x126/0x1f0 drivers/tty/pty.c:122 <-- lock(&port->lock); > n_tty_write+0xa7a/0xfc0 drivers/tty/n_tty.c:2356 > do_tty_write drivers/tty/tty_io.c:961 [inline] > tty_write+0x512/0x930 drivers/tty/tty_io.c:1045 > __vfs_write+0x76/0x100 fs/read_write.c:494 > [...] > > other info that might help us debug this: > > Chain exists of: > console_owner --> &port_lock_key --> &port->lock > > Fixes: b6da31b2c07c ("tty: Fix data race in tty_insert_flip_string_fixed_flag") > Signed-off-by: Qi Zheng > Acked-by: Jiri Slaby Acked-by: Greg Kroah-Hartman