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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 14D0AC0650F for ; Tue, 30 Jul 2019 12:07:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E7EF92087F for ; Tue, 30 Jul 2019 12:07:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729612AbfG3MH4 (ORCPT ); Tue, 30 Jul 2019 08:07:56 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:56557 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729191AbfG3MHx (ORCPT ); Tue, 30 Jul 2019 08:07:53 -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 1hsQuM-0006QL-Op; Tue, 30 Jul 2019 14:07:10 +0200 Message-Id: <20190730120321.393759046@linutronix.de> User-Agent: quilt/0.65 Date: Tue, 30 Jul 2019 13:24:55 +0200 From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Ingo Molnar , Sebastian Siewior , Anna-Maria Gleixner , Steven Rostedt , Julia Cartwright , "Theodore Tso" , Alexander Viro , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Jan Kara Subject: [patch 3/4] fs/buffer: Substitute BH_Uptodate_Lock for RT and bit spinlock debugging References: <20190730112452.871257694@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: "Theodore Ts'o" Cc: Alexander Viro Cc: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org --- 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.