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 A2FDEC04A68 for ; Wed, 27 Jul 2022 16:22:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235256AbiG0QWd (ORCPT ); Wed, 27 Jul 2022 12:22:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234884AbiG0QWK (ORCPT ); Wed, 27 Jul 2022 12:22:10 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E45294B0DB; Wed, 27 Jul 2022 09:22:08 -0700 (PDT) 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 ams.source.kernel.org (Postfix) with ESMTPS id 7621BB821B9; Wed, 27 Jul 2022 16:22:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E6F6C433D6; Wed, 27 Jul 2022 16:22:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1658938926; bh=kFhuF2RVQuecvw5Ummki3VCBeoRSPFC+QkKqQkR6Egg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=IMnbXG15sMpSh5mqExUgfjWdF5Fj3wXlJnxaHzakbPPQMDt1JbJ8ctIq8kUfgadse +bqYUSEKpd81GoSqalFguYil1YZA/m270LuwZWnxYYyW2+4agG8veJ2CuV5XLyj9yl ti0q+4XIvdcNChdGsZCdqXnra1CiFNEC17ytNe5Y= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Sergey Senozhatsky , Qian Cai , Lech Perczak , Theodore Tso , Sasha Levin , Petr Mladek , John Ogness , kernel test robot , "Jason A. Donenfeld" Subject: [PATCH 4.9 17/26] Revert "Revert "char/random: silence a lockdep splat with printk()"" Date: Wed, 27 Jul 2022 18:10:46 +0200 Message-Id: <20220727160959.806070508@linuxfoundation.org> X-Mailer: git-send-email 2.37.1 In-Reply-To: <20220727160959.122591422@linuxfoundation.org> References: <20220727160959.122591422@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Jason A. Donenfeld" In 2019, Sergey fixed a lockdep splat with 15341b1dd409 ("char/random: silence a lockdep splat with printk()"), but that got reverted soon after from 4.19 because back then it apparently caused various problems. But the issue it was fixing is still there, and more generally, many patches turning printk() into printk_deferred() have landed since, making me suspect it's okay to try this out again. This should fix the following deadlock found by the kernel test robot: [ 18.287691] WARNING: possible circular locking dependency detected [ 18.287692] 4.19.248-00165-g3d1f971aa81f #1 Not tainted [ 18.287693] ------------------------------------------------------ [ 18.287712] stop/202 is trying to acquire lock: [ 18.287713] (ptrval) (console_owner){..-.}, at: console_unlock (??:?) [ 18.287717] [ 18.287718] but task is already holding lock: [ 18.287718] (ptrval) (&(&port->lock)->rlock){-...}, at: pty_write (pty.c:?) [ 18.287722] [ 18.287722] which lock already depends on the new lock. [ 18.287723] [ 18.287724] [ 18.287725] the existing dependency chain (in reverse order) is: [ 18.287725] [ 18.287726] -> #2 (&(&port->lock)->rlock){-...}: [ 18.287729] validate_chain+0x84a/0xe00 [ 18.287729] __lock_acquire (lockdep.c:?) [ 18.287730] lock_acquire (??:?) [ 18.287731] _raw_spin_lock_irqsave (??:?) [ 18.287732] tty_port_tty_get (??:?) [ 18.287733] tty_port_default_wakeup (tty_port.c:?) [ 18.287734] tty_port_tty_wakeup (??:?) [ 18.287734] uart_write_wakeup (??:?) [ 18.287735] serial8250_tx_chars (??:?) [ 18.287736] serial8250_handle_irq (??:?) [ 18.287737] serial8250_default_handle_irq (8250_port.c:?) [ 18.287738] serial8250_interrupt (8250_core.c:?) [ 18.287738] __handle_irq_event_percpu (??:?) [ 18.287739] handle_irq_event_percpu (??:?) [ 18.287740] handle_irq_event (??:?) [ 18.287741] handle_edge_irq (??:?) [ 18.287742] handle_irq (??:?) [ 18.287742] do_IRQ (??:?) [ 18.287743] common_interrupt (entry_32.o:?) [ 18.287744] _raw_spin_unlock_irqrestore (??:?) [ 18.287745] uart_write (serial_core.c:?) [ 18.287746] process_output_block (n_tty.c:?) [ 18.287747] n_tty_write (n_tty.c:?) [ 18.287747] tty_write (tty_io.c:?) [ 18.287748] __vfs_write (??:?) [ 18.287749] vfs_write (??:?) [ 18.287750] ksys_write (??:?) [ 18.287750] sys_write (??:?) [ 18.287751] do_fast_syscall_32 (??:?) [ 18.287752] entry_SYSENTER_32 (??:?) [ 18.287752] [ 18.287753] -> #1 (&port_lock_key){-.-.}: [ 18.287756] [ 18.287756] -> #0 (console_owner){..-.}: [ 18.287759] check_prevs_add (lockdep.c:?) [ 18.287760] validate_chain+0x84a/0xe00 [ 18.287761] __lock_acquire (lockdep.c:?) [ 18.287761] lock_acquire (??:?) [ 18.287762] console_unlock (??:?) [ 18.287763] vprintk_emit (??:?) [ 18.287764] vprintk_default (??:?) [ 18.287764] vprintk_func (??:?) [ 18.287765] printk (??:?) [ 18.287766] get_random_u32 (??:?) [ 18.287767] shuffle_freelist (slub.c:?) [ 18.287767] allocate_slab (slub.c:?) [ 18.287768] new_slab (slub.c:?) [ 18.287769] ___slab_alloc+0x6d0/0xb20 [ 18.287770] __slab_alloc+0xd6/0x2e0 [ 18.287770] __kmalloc (??:?) [ 18.287771] tty_buffer_alloc (tty_buffer.c:?) [ 18.287772] __tty_buffer_request_room (tty_buffer.c:?) [ 18.287773] tty_insert_flip_string_fixed_flag (??:?) [ 18.287774] pty_write (pty.c:?) [ 18.287775] process_output_block (n_tty.c:?) [ 18.287776] n_tty_write (n_tty.c:?) [ 18.287777] tty_write (tty_io.c:?) [ 18.287778] __vfs_write (??:?) [ 18.287779] vfs_write (??:?) [ 18.287780] ksys_write (??:?) [ 18.287780] sys_write (??:?) [ 18.287781] do_fast_syscall_32 (??:?) [ 18.287782] entry_SYSENTER_32 (??:?) [ 18.287783] [ 18.287783] other info that might help us debug this: [ 18.287784] [ 18.287785] Chain exists of: [ 18.287785] console_owner --> &port_lock_key --> &(&port->lock)->rlock [ 18.287789] [ 18.287790] Possible unsafe locking scenario: [ 18.287790] [ 18.287791] CPU0 CPU1 [ 18.287792] ---- ---- [ 18.287792] lock(&(&port->lock)->rlock); [ 18.287794] lock(&port_lock_key); [ 18.287814] lock(&(&port->lock)->rlock); [ 18.287815] lock(console_owner); [ 18.287817] [ 18.287818] *** DEADLOCK *** [ 18.287818] [ 18.287819] 6 locks held by stop/202: [ 18.287820] #0: (ptrval) (&tty->ldisc_sem){++++}, at: ldsem_down_read (??:?) [ 18.287823] #1: (ptrval) (&tty->atomic_write_lock){+.+.}, at: tty_write_lock (tty_io.c:?) [ 18.287826] #2: (ptrval) (&o_tty->termios_rwsem/1){++++}, at: n_tty_write (n_tty.c:?) [ 18.287830] #3: (ptrval) (&ldata->output_lock){+.+.}, at: process_output_block (n_tty.c:?) [ 18.287834] #4: (ptrval) (&(&port->lock)->rlock){-...}, at: pty_write (pty.c:?) [ 18.287838] #5: (ptrval) (console_lock){+.+.}, at: console_trylock_spinning (printk.c:?) [ 18.287841] [ 18.287842] stack backtrace: [ 18.287843] CPU: 0 PID: 202 Comm: stop Not tainted 4.19.248-00165-g3d1f971aa81f #1 [ 18.287843] Call Trace: [ 18.287844] dump_stack (??:?) [ 18.287845] print_circular_bug.cold+0x78/0x8b [ 18.287846] check_prev_add+0x66a/0xd20 [ 18.287847] check_prevs_add (lockdep.c:?) [ 18.287848] validate_chain+0x84a/0xe00 [ 18.287848] __lock_acquire (lockdep.c:?) [ 18.287849] lock_acquire (??:?) [ 18.287850] ? console_unlock (??:?) [ 18.287851] console_unlock (??:?) [ 18.287851] ? console_unlock (??:?) [ 18.287852] ? native_save_fl (??:?) [ 18.287853] vprintk_emit (??:?) [ 18.287854] vprintk_default (??:?) [ 18.287855] vprintk_func (??:?) [ 18.287855] printk (??:?) [ 18.287856] get_random_u32 (??:?) [ 18.287857] ? shuffle_freelist (slub.c:?) [ 18.287858] shuffle_freelist (slub.c:?) [ 18.287858] ? page_address (??:?) [ 18.287859] allocate_slab (slub.c:?) [ 18.287860] new_slab (slub.c:?) [ 18.287861] ? pvclock_clocksource_read (??:?) [ 18.287862] ___slab_alloc+0x6d0/0xb20 [ 18.287862] ? kvm_sched_clock_read (kvmclock.c:?) [ 18.287863] ? __slab_alloc+0xbc/0x2e0 [ 18.287864] ? native_wbinvd (paravirt.c:?) [ 18.287865] __slab_alloc+0xd6/0x2e0 [ 18.287865] __kmalloc (??:?) [ 18.287866] ? __lock_acquire (lockdep.c:?) [ 18.287867] ? tty_buffer_alloc (tty_buffer.c:?) [ 18.287868] tty_buffer_alloc (tty_buffer.c:?) [ 18.287869] __tty_buffer_request_room (tty_buffer.c:?) [ 18.287869] tty_insert_flip_string_fixed_flag (??:?) [ 18.287870] pty_write (pty.c:?) [ 18.287871] process_output_block (n_tty.c:?) [ 18.287872] n_tty_write (n_tty.c:?) [ 18.287873] ? print_dl_stats (??:?) [ 18.287874] ? n_tty_ioctl (n_tty.c:?) [ 18.287874] tty_write (tty_io.c:?) [ 18.287875] ? n_tty_ioctl (n_tty.c:?) [ 18.287876] ? tty_write_unlock (tty_io.c:?) [ 18.287877] __vfs_write (??:?) [ 18.287877] vfs_write (??:?) [ 18.287878] ? __fget_light (file.c:?) [ 18.287879] ksys_write (??:?) Cc: Sergey Senozhatsky Cc: Qian Cai Cc: Lech Perczak Cc: Greg Kroah-Hartman Cc: Theodore Ts'o Cc: Sasha Levin Cc: Petr Mladek Cc: John Ogness Reported-by: kernel test robot Link: https://lore.kernel.org/lkml/Ytz+lo4zRQYG3JUR@xsang-OptiPlex-9020 Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -184,8 +184,8 @@ static void __cold process_random_ready_ #define warn_unseeded_randomness() \ if (IS_ENABLED(CONFIG_WARN_ALL_UNSEEDED_RANDOM) && !crng_ready()) \ - pr_notice("%s called from %pS with crng_init=%d\n", \ - __func__, (void *)_RET_IP_, crng_init) + printk_deferred(KERN_NOTICE "random: %s called from %pS with crng_init=%d\n", \ + __func__, (void *)_RET_IP_, crng_init) /*********************************************************************