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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 B811AC4338F for ; Fri, 13 Aug 2021 17:27:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9AD6360F36 for ; Fri, 13 Aug 2021 17:27:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232392AbhHMR2I (ORCPT ); Fri, 13 Aug 2021 13:28:08 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:38046 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229554AbhHMR2G (ORCPT ); Fri, 13 Aug 2021 13:28:06 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1628875658; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hXTaSydLQd13Wt3GN8lQTythfyuBI5u6fx4bdjj3qSg=; b=VLTc/NGS01W+I7Tlg4jxZ/rgRXF32oKOJjtdocgDY+RPIkowZnl3vDNsWUcC4q4Yga2BMF 2wbW+YBdmz1PBFt+LXhB6OqnJ8DzTPNb8Sdg1yQsN7lG69N4Wc97lJxUrCmhyX1fu/rCD9 eUSK8XWfLmzJUCWEFSnWCrJ9gwcb/QoK4xQk6nS5go0yrbop8VoO8HIFKOix4VM8l2/qfW vuAtle7ZBCVS35jtLccUg8RbuPF9IuNWWJn/RNQwhV+abr5nkr42IAJbuI8YHr5J/XG2bO ONgm+C4Pt/KYIQ4wb4sJx3ESzwBz6d2wSKMFb8L1x7z+mthbGBJPCk9sH6To4w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1628875658; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hXTaSydLQd13Wt3GN8lQTythfyuBI5u6fx4bdjj3qSg=; b=+C58gskZdXfZhavBAInUT9TFk9MBa4c7jqWdWExTuhHBWCGEBVHtqq9BHpJftcWd409HWO bNhtQ37dB9iXedBQ== To: Waiman Long , Xiaoming Ni , linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com Cc: wangle6@huawei.com, xiaoqian9@huawei.com, shaolexi@huawei.com Subject: Re: [PATCH] semaphore: Add might_sleep() to down_*() family In-Reply-To: <48cddad4-0388-ae8b-f98b-1629b9ae590a@redhat.com> References: <20210809021215.19991-1-nixiaoming@huawei.com> <48cddad4-0388-ae8b-f98b-1629b9ae590a@redhat.com> Date: Fri, 13 Aug 2021 19:27:37 +0200 Message-ID: <877dgpp852.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Aug 08 2021 at 23:01, Waiman Long wrote: > On 8/8/21 10:12 PM, Xiaoming Ni wrote: >> Semaphore is sleeping lock. Add might_sleep() to down*() family >> (with exception of down_trylock()) to detect atomic context sleep. >> @@ -157,6 +160,7 @@ int down_timeout(struct semaphore *sem, long timeout) >> unsigned long flags; >> int result = 0; >> >> + might_sleep(); >> raw_spin_lock_irqsave(&sem->lock, flags); >> if (likely(sem->count > 0)) >> sem->count--; > > I think it is simpler to just put a "might_sleep()" in __down_common() > which is the function where sleep can actually happen. No. Putting it in __down_common() is wrong, because that covers only the contended case. But we want to cover the potential sleep, i.e. checking even in the non-contended case, which is what might_sleep() is about. Thanks, tglx