From patchwork Thu Aug 1 01:01:29 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Thomas Gleixner X-Patchwork-Id: 11069863 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D676D13A4 for ; Thu, 1 Aug 2019 01:16:47 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C933527F98 for ; Thu, 1 Aug 2019 01:16:47 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id BC87528173; Thu, 1 Aug 2019 01:16:47 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A574127F98 for ; Thu, 1 Aug 2019 01:16:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729437AbfHABQj (ORCPT ); Wed, 31 Jul 2019 21:16:39 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:33544 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729398AbfHABQh (ORCPT ); Wed, 31 Jul 2019 21:16:37 -0400 Received: from localhost ([127.0.0.1] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1hszhH-0002IA-Ks; Thu, 01 Aug 2019 03:15:59 +0200 Message-Id: <20190801010944.174039805@linutronix.de> User-Agent: quilt/0.65 Date: Thu, 01 Aug 2019 03:01:29 +0200 From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Ingo Molnar , Sebastian Siewior , Anna-Maria Gleixner , Steven Rostedt , Julia Cartwright , Jan Kara , "Theodore Tso" , Alexander Viro , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Jan Kara , Mark Fasheh , Joseph Qi , Joel Becker Subject: [patch V2 3/7] fs/buffer: Substitute BH_Uptodate_Lock for RT and bit spinlock debugging References: <20190801010126.245731659@linutronix.de> MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Bit spinlocks are problematic if PREEMPT_RT is enabled. They disable preemption, which is undesired for latency reasons and breaks when regular spinlocks are taken within the bit_spinlock locked region because regular spinlocks are converted to 'sleeping spinlocks' on RT. Substitute the BH_Uptodate_Lock bit spinlock with a regular spinlock for PREEMPT_RT enabled kernels. Bit spinlocks are also not covered by lock debugging, e.g. lockdep. With the spinlock substitution in place, they can be exposed via CONFIG_DEBUG_BIT_SPINLOCKS. Signed-off-by: Thomas Gleixner Reviewed-by: Jan Kara Cc: "Theodore Ts'o" Cc: Alexander Viro Cc: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org --- V2: Collected Reviewed-by tag --- fs/buffer.c | 1 + include/linux/buffer_head.h | 31 +++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) --- a/fs/buffer.c +++ b/fs/buffer.c @@ -3360,6 +3360,7 @@ struct buffer_head *alloc_buffer_head(gf struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags); if (ret) { INIT_LIST_HEAD(&ret->b_assoc_buffers); + buffer_head_init_locks(ret); preempt_disable(); __this_cpu_inc(bh_accounting.nr); recalc_bh_state(); --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -76,8 +76,35 @@ struct buffer_head { struct address_space *b_assoc_map; /* mapping this buffer is associated with */ atomic_t b_count; /* users using this buffer_head */ + +#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_DEBUG_BIT_SPINLOCKS) + spinlock_t b_uptodate_lock; +#endif }; +#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_DEBUG_BIT_SPINLOCKS) + +static inline unsigned long bh_uptodate_lock_irqsave(struct buffer_head *bh) +{ + unsigned long flags; + + spin_lock_irqsave(&bh->b_uptodate_lock, flags); + return flags; +} + +static inline void +bh_uptodate_unlock_irqrestore(struct buffer_head *bh, unsigned long flags) +{ + spin_unlock_irqrestore(&bh->b_uptodate_lock, flags); +} + +static inline void buffer_head_init_locks(struct buffer_head *bh) +{ + spin_lock_init(&bh->b_uptodate_lock); +} + +#else /* PREEMPT_RT || DEBUG_BIT_SPINLOCKS */ + static inline unsigned long bh_uptodate_lock_irqsave(struct buffer_head *bh) { unsigned long flags; @@ -94,6 +121,10 @@ bh_uptodate_unlock_irqrestore(struct buf local_irq_restore(flags); } +static inline void buffer_head_init_locks(struct buffer_head *bh) { } + +#endif /* !PREEMPT_RT && !DEBUG_BIT_SPINLOCKS */ + /* * macro tricks to expand the set_buffer_foo(), clear_buffer_foo() * and buffer_foo() functions.