From patchwork Wed Oct 19 14:55:22 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Ogness X-Patchwork-Id: 616578 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 D3552C43219 for ; Wed, 19 Oct 2022 15:03:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231814AbiJSPDA (ORCPT ); Wed, 19 Oct 2022 11:03:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231313AbiJSPCq (ORCPT ); Wed, 19 Oct 2022 11:02:46 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CA8F9161FD4; Wed, 19 Oct 2022 07:57:25 -0700 (PDT) From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1666191362; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=zkI+7kE11pEfvJZCSjIsOIHfnjIhjBs6goKb/AUL2D4=; b=YYO7v04TmKSkEL8SQfYf9FANh400BpV31ZQR/trpNhqYtbMsqHy7XZuAyWZcYguh+KTZKz uMkqVYF2Idk8ssJy6cSwkhJih5dltGrVFm3Z7MoL7Nhtw4GkmZEKblfArE1vVoKGDs5p81 WHY9OAlLqzr8G07YBDVNtY0AT4QClPosfQAXC7SCLUuMtHyHR5c2LCkNDByg36nTiuRcRN AVWPIk+/COT66KSdFzs7sxleUpL2onRYs8JoVdAMBeDCEkOf8Yvmkp92DVD8xjN57OewPI lAF6m3iPq5588431gmChW8+srrThoCLrEllt8f0GsYtka8ApK0mxiWi8JG1KQQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1666191362; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=zkI+7kE11pEfvJZCSjIsOIHfnjIhjBs6goKb/AUL2D4=; b=taXn8qnVlav1KthfUzD2BUf7770pohYL/ecGjx8VGuNp3NOcr/dyz4UXH5Ok4L9J1BRVse cqmXXqp/T3jlr9Bg== To: Petr Mladek Cc: Sergey Senozhatsky , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Jason Wessel , "Paul E. McKenney" , Daniel Thompson , Douglas Anderson , Greg Kroah-Hartman , Jiri Slaby , kgdb-bugreport@lists.sourceforge.net, linux-serial@vger.kernel.org, linux-fsdevel@vger.kernel.org, Miguel Ojeda , Geert Uytterhoeven , linux-m68k@lists.linux-m68k.org, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Ard Biesheuvel , linux-efi@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, Shile Zhang , Xianting Tian , linuxppc-dev@lists.ozlabs.org, Krzysztof Kozlowski , Alim Akhtar , linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, Michal Simek , Peter Zijlstra , Mike Rapoport , Mathias Nyman , Andrew Morton , linux-usb@vger.kernel.org, Luis Chamberlain , Aaron Tomlin , Helge Deller , Thomas Zimmermann , Javier Martinez Canillas , Boris Ostrovsky , Juergen Gross , Tom Rix , linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: [PATCH printk v2 00/38] reduce console_lock scope Date: Wed, 19 Oct 2022 17:01:22 +0206 Message-Id: <20221019145600.1282823-1-john.ogness@linutronix.de> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org This is v2 of a series to prepare for threaded/atomic printing. It is a rework of patches 6-12 of the v1 [0]. From the v1, patches 1-5 are already mainline and a rework of patches >12 will be posted in a later series. This series focuses on reducing the scope of the BKL console_lock. It achieves this by switching to SRCU and a dedicated mutex for console list iteration and modification, respectively. The console_lock will no longer offer this protection and is completely removed from (un)register_console() and console_stop/start() code. All users of the console_lock for list iteration have been modified. For the call sites where the console_lock is still needed (because of other reasons), I added comments to explain exactly why the console_lock was needed. The base commit for this series is from Paul McKenney's RCU tree and provides an NMI-safe SRCU implementation [1]. Without the NMI-safe SRCU implementation, this series is not less safe than mainline. But we will need the NMI-safe SRCU implementation for atomic consoles anyway, so we might as well get it in now. Especially since it _does_ increase the reliability for mainline in the panic path. Changes since v2: general: - introduce console_is_enabled() to document safe data race on console->flags - switch all "console->flags & CON_ENABLED" code sites to console_is_enabled() - add "for_each_console_srcu" to .clang-format - cleanup/clarify comments relating to console_lock coverage/usage um: - kmsg_dumper: use srcu instead of console_lock for list iteration kgdb/kdb: - configure_kgdboc: keep console_lock for console->device() synchronization, use srcu for list iteration - kgdboc_earlycon_pre_exp_handler: use srcu instead of documenting unsafety for list iteration - kgdboc_earlycon_init: use console_list_lock instead of console_lock to lock list - kdb_msg_write: use srcu instead of documenting unsafety for list iteration tty: - show_cons_active: keep console_lock for console->device() synchronization fbdev: - xen-fbfront: xenfb_probe: use srcu instead of console_lock for list iteration, introduce console_force_preferred() to safely implement hack proc/consoles: - show_console_dev: keep console_lock for console->device() synchronization - c_next: use hlist_entry_safe() instead of hlist_for_each_entry_continue() printk: - remove console_lock from console_stop/start() and (un)register_console() - introduce console_srcu_read_(un)lock() to wrap scru read (un)lock - rename cons_first() macro to console_first() - for_each_console: add lockdep check instead of introducing new for_each_registered_console() - console_list_lock: add warning if in read-side critical section - release srcu read lock on handover - console_flush_all: use srcu instead of relying on console lock for list iteration - console_unblank: use srcu instead of relying on console_lock for list iteration - console_flush_on_panic: use srcu for list iteration and document console->seq race - device: keep console_lock for console->device() synchronization, usr srcu for list iteration - register_console: split list adding logic into the 3 distinct scenarios - register_console: set initial sequence number before adding to list - unregister_console: fix ENODEV return value if the console is not registered - console_stop: synchronize srcu - printk_late_init: use _safe variant of iteration - __pr_flush: use srcu instead of relying on console_lock for list iteration John Ogness [0] https://lore.kernel.org/r/20220924000454.3319186-1-john.ogness@linutronix.de [1] https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/log/?h=srcunmisafe.2022.10.18b John Ogness (37): printk: Convert console_drivers list to hlist printk: Prepare for SRCU console list protection printk: introduce console_is_enabled() wrapper printk: use console_is_enabled() tty: nfcon: use console_is_enabled() um: kmsg_dump: use console_is_enabled() efi: earlycon: use console_is_enabled() netconsole: use console_is_enabled() tty: hvc: use console_is_enabled() tty: serial: earlycon: use console_is_enabled() tty: serial: kgdboc: use console_is_enabled() tty: serial: pic32_uart: use console_is_enabled() tty: serial: samsung_tty: use console_is_enabled() tty: serial: serial_core: use console_is_enabled() tty: serial: xilinx_uartps: use console_is_enabled() tty: tty_io: use console_is_enabled() usb: early: xhci-dbc: use console_is_enabled() kdb: kdb_io: use console_is_enabled() um: kmsg_dumper: use srcu console list iterator serial: kgdboc: use srcu console list iterator serial: kgdboc: document console_lock usage tty: tty_io: document console_lock usage xen: fbfront: use srcu console list iterator proc: consoles: document console_lock usage kdb: use srcu console list iterator printk: console_flush_all: use srcu console list iterator printk: console_unblank: use srcu console list iterator printk: console_flush_on_panic: use srcu console list iterator printk: console_device: use srcu console list iterator printk: register_console: use srcu console list iterator printk: __pr_flush: use srcu console list iterator printk: introduce console_list_lock serial: kgdboc: use console_list_lock instead of console_lock tty: tty_io: use console_list_lock for list synchronization proc: consoles: use console_list_lock for list iteration printk: relieve console_lock of list synchronization duties printk, xen: fbfront: create/use safe function for forcing preferred Thomas Gleixner (1): serial: kgdboc: Lock console list in probe function .clang-format | 1 + arch/m68k/emu/nfcon.c | 4 +- arch/um/kernel/kmsg_dump.c | 15 +- drivers/firmware/efi/earlycon.c | 4 +- drivers/net/netconsole.c | 4 +- drivers/tty/hvc/hvc_console.c | 2 +- drivers/tty/serial/earlycon.c | 4 +- drivers/tty/serial/kgdboc.c | 37 ++- drivers/tty/serial/pic32_uart.c | 2 +- drivers/tty/serial/samsung_tty.c | 2 +- drivers/tty/serial/serial_core.c | 2 +- drivers/tty/serial/xilinx_uartps.c | 2 +- drivers/tty/tty_io.c | 18 +- drivers/usb/early/xhci-dbc.c | 2 +- drivers/video/fbdev/xen-fbfront.c | 16 +- fs/proc/consoles.c | 20 +- include/linux/console.h | 75 +++++- include/linux/serial_core.h | 2 +- kernel/debug/kdb/kdb_io.c | 7 +- kernel/printk/printk.c | 373 +++++++++++++++++++++-------- 20 files changed, 438 insertions(+), 154 deletions(-) base-commit: c2d158a284abd63d727dad7402a2eed650dd4233