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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B338CEB64DC for ; Tue, 11 Jul 2023 23:38:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=lists.ozlabs.org; s=201707; t=1689118723; bh=VlZMY7B4OQtHfVwCl2fGa87UX0dm/HNDQvgsMerbs4E=; h=Date:Subject:To:List-Id:List-Unsubscribe:List-Archive:List-Post: List-Help:List-Subscribe:From:Reply-To:Cc:From; b=il+yohW5LmxiO0a0+OXe3a02tNaJpb/Vbq8RNJKDo1XhBHlx3U15w5aACL3LARDVq 6RUV9VXAOiqZb5IT5YiB0IMBjbt6A/W/rttEpPaA3PVn8vt3fiT+dicz0fnxNNv5nk jT0axT57hXdh/YHI00+dgqUc4EvjCjI5FmWQUZZ7kkpsM66qqMYg2H7t73NQfYz/H3 WmtwDtDyaw29juR3sj7+upmgs3fL2vWQCdvyE5dlfthkCsVkIY4korcwo6i0Wft5hx ZENnPL0fqRPxZ+x3Lm8qJQO9eEpSPFI1MokrdVaCArNwA/sU4aYM038tbAVuEZWkj9 +Ymxobt1Z6ClQ== Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4R0y4M6nvFz3bwg for ; Wed, 12 Jul 2023 09:38:43 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20221208 header.b=6Ki0rULe; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=flex--dhavale.bounces.google.com (client-ip=2607:f8b0:4864:20::549; helo=mail-pg1-x549.google.com; envelope-from=39-etzackc6onrkfkvoqyyqvo.mywvsxeh-obypcvscdc.yjvklc.ybq@flex--dhavale.bounces.google.com; receiver=lists.ozlabs.org) Received: from mail-pg1-x549.google.com (mail-pg1-x549.google.com [IPv6:2607:f8b0:4864:20::549]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4R0y4G3CWgz30PJ for ; Wed, 12 Jul 2023 09:38:36 +1000 (AEST) Received: by mail-pg1-x549.google.com with SMTP id 41be03b00d2f7-53450fa3a18so8770824a12.0 for ; Tue, 11 Jul 2023 16:38:36 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689118711; x=1691710711; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=VlZMY7B4OQtHfVwCl2fGa87UX0dm/HNDQvgsMerbs4E=; b=F6XuiTQdXq8RLmiuq+pupDRXkLZVCFpFluSU5upUN4JVjyeufKX348hNwgjfXl/IAo g5Ds9uMRXHoDYLzIbQBAJ0ZGBaY/ks74nwH/LW2rxgp3XarYhhiRDIlUyV3C+GDnSxyl Ph4JqvmHCghsr4xSv+8s/oL3cax2hTOJ2Qkz7snwsQgt9hopQAQ/A6TpepqR1WMkV460 m6CZKC/waOuejy6P/CNn9oI1N81t/9CWF+aHTe5zPfwUz5ULRAtdvSTQa5T5WyPY96RG XPaA1ODSH/dC5ujxVOJj8pJnB1UB/COgMCn96psp8uCaqXbnRzevU/NdHBHH+0PmB8xy JSBg== X-Gm-Message-State: ABy/qLYF8SVy1WyJfFPYWJDsikE57Ph4TU00/l+IV9PgykZJ07olemSn 4Y10yyefTqrzFQo6rrzv8HHZvBbhA7hM X-Google-Smtp-Source: APBJJlEh1KFYgX73qa7oSh36gSCXi/QGqv/5l19pZiBs2u+PQkzFrZtGOa0EdwtmAe2WF+om3uaJkkHyZ7t9 X-Received: from dhavale-ctop.c.googlers.com ([fda3:e722:ac3:cc00:24:72f4:c0a8:5e39]) (user=dhavale job=sendgmr) by 2002:a63:9511:0:b0:55c:2f9f:e427 with SMTP id p17-20020a639511000000b0055c2f9fe427mr4581555pgd.5.1689118711049; Tue, 11 Jul 2023 16:38:31 -0700 (PDT) Date: Tue, 11 Jul 2023 16:38:15 -0700 Mime-Version: 1.0 X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog Message-ID: <20230711233816.2187577-1-dhavale@google.com> Subject: [PATCH v1] rcu: Fix and improve RCU read lock checks when !CONFIG_DEBUG_LOCK_ALLOC To: "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Matthias Brugger , AngeloGioacchino Del Regno Content-Type: text/plain; charset="UTF-8" X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Sandeep Dhavale via Linux-erofs Reply-To: Sandeep Dhavale Cc: Will Shiu , linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-mediatek@lists.infradead.org, kernel-team@android.com, linux-arm-kernel@lists.infradead.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" Currently if CONFIG_DEBUG_LOCK_ALLOC is not set - rcu_read_lock_held() always returns 1 - rcu_read_lock_any_held() may return 0 with CONFIG_PREEMPT_RCU This is inconsistent and it was discovered when trying a fix for problem reported [1] with CONFIG_DEBUG_LOCK_ALLOC is not set and CONFIG_PREEMPT_RCU is enabled. Gist of the problem is that EROFS wants to detect atomic context so it can do inline decompression whenever possible, this is important performance optimization. It turns out that z_erofs_decompressqueue_endio() can be called from blk_mq_flush_plug_list() with rcu lock held and hence fix uses rcu_read_lock_any_held() to decide to use sync/inline decompression vs async decompression. As per documentation, we should return lock is held if we aren't certain. But it seems we can improve the checks for if the lock is held even if CONFIG_DEBUG_LOCK_ALLOC is not set instead of hardcoding to always return true. * rcu_read_lock_held() - For CONFIG_PREEMPT_RCU using rcu_preempt_depth() - using preemptible() (indirectly preempt_count()) * rcu_read_lock_bh_held() - For CONFIG_PREEMPT_RT Using in_softirq() (indirectly softirq_cont()) - using preemptible() (indirectly preempt_count()) Lastly to fix the inconsistency, rcu_read_lock_any_held() is updated to use other rcu_read_lock_*_held() checks. Two of the improved checks are moved to kernel/rcu/update.c because rcupdate.h is included from the very low level headers which do not know what current (task_struct) is so the macro rcu_preempt_depth() cannot be expanded in the rcupdate.h. See the original comment for rcu_preempt_depth() in patch at [2] for more information. [1] https://lore.kernel.org/all/20230621220848.3379029-1-dhavale@google.com/ [2] https://lore.kernel.org/all/1281392111-25060-8-git-send-email-paulmck@linux.vnet.ibm.com/ Reported-by: Will Shiu Signed-off-by: Sandeep Dhavale --- include/linux/rcupdate.h | 12 +++--------- kernel/rcu/update.c | 21 ++++++++++++++++++++- 2 files changed, 23 insertions(+), 10 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 5e5f920ade90..0d1d1d8c2360 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -319,14 +319,11 @@ int rcu_read_lock_any_held(void); # define rcu_lock_acquire(a) do { } while (0) # define rcu_lock_release(a) do { } while (0) -static inline int rcu_read_lock_held(void) -{ - return 1; -} +int rcu_read_lock_held(void); static inline int rcu_read_lock_bh_held(void) { - return 1; + return !preemptible() || in_softirq(); } static inline int rcu_read_lock_sched_held(void) @@ -334,10 +331,7 @@ static inline int rcu_read_lock_sched_held(void) return !preemptible(); } -static inline int rcu_read_lock_any_held(void) -{ - return !preemptible(); -} +int rcu_read_lock_any_held(void); static inline int debug_lockdep_rcu_enabled(void) { diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 19bf6fa3ee6a..b34fc5bb96cf 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -390,8 +390,27 @@ int rcu_read_lock_any_held(void) } EXPORT_SYMBOL_GPL(rcu_read_lock_any_held); -#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ +#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ +int rcu_read_lock_held(void) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RCU)) + return rcu_preempt_depth(); + return !preemptible(); +} +EXPORT_SYMBOL_GPL(rcu_read_lock_held); + +int rcu_read_lock_any_held(void) +{ + if (rcu_read_lock_held() || + rcu_read_lock_bh_held() || + rcu_read_lock_sched_held()) + return 1; + return !preemptible(); +} +EXPORT_SYMBOL_GPL(rcu_read_lock_any_held); + +#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ /** * wakeme_after_rcu() - Callback function to awaken a task after grace period * @head: Pointer to rcu_head member within rcu_synchronize structure -- 2.41.0.255.g8b1d071c50-goog