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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7E386C02180 for ; Thu, 16 Jan 2025 10:52:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id ED0006B0085; Thu, 16 Jan 2025 05:52:57 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E80ED280001; Thu, 16 Jan 2025 05:52:57 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D6EBF6B0089; Thu, 16 Jan 2025 05:52:57 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id B91A76B0085 for ; Thu, 16 Jan 2025 05:52:57 -0500 (EST) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 4B32FC0A23 for ; Thu, 16 Jan 2025 10:52:57 +0000 (UTC) X-FDA: 83013002394.19.4524AF9 Received: from mail115-100.sinamail.sina.com.cn (mail115-100.sinamail.sina.com.cn [218.30.115.100]) by imf26.hostedemail.com (Postfix) with ESMTP id 9DB4D14000A for ; Thu, 16 Jan 2025 10:52:53 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf26.hostedemail.com: domain of hdanton@sina.com designates 218.30.115.100 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1737024775; a=rsa-sha256; cv=none; b=0RWIRZ6sPLpmz6fcLv7YZZQyjbEG7oCholGqjqZoLL5yxltR05tD+a8Ad/61I061UkTGZT W8IBzYLd3hoOc3COXvdkyx4Oev3CRkHmapG82qftBMvieXu0ltCJk1gJvFrGieVJFl92FN zIs+B9NMv1K5g5LOcyGWylYAF+xGkB4= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf26.hostedemail.com: domain of hdanton@sina.com designates 218.30.115.100 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1737024775; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=IoegOPUco33okZnaoDatxokPgBdbj9wF/snD0D8Njc8=; b=x+6TgQC9cCtwZlc04ULN9zsfHQq1qDarygQxNypZc4/8ConPLCQcsix7Z///ba7Oz3xKSw cnqvqLfcaTnwZMlNapKJj1PZNHYWRx55QerCA5q8jpNCh/xoiuUa13FveQQ4lWExrfsGgJ 49OqmK7QHp1bXP5M+3rvV9Itn+xS51w= X-SMAIL-HELO: localhost.localdomain Received: from unknown (HELO localhost.localdomain)([113.118.66.228]) by sina.com (10.185.250.23) with ESMTP id 6788E4FD00006B88; Thu, 16 Jan 2025 18:52:48 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 709908913235 X-SMAIL-UIID: 81EC6948B6094F3080A5292AD3ED5E7F-20250116-185248-1 From: Hillf Danton To: Peter Zijlstra Cc: Suren Baghdasaryan , akpm@linux-foundation.org, willy@infradead.org, hannes@cmpxchg.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v9 10/17] refcount: introduce __refcount_{add|inc}_not_zero_limited Date: Thu, 16 Jan 2025 18:52:35 +0800 Message-ID: <20250116105236.1916-1-hdanton@sina.com> In-Reply-To: <20250115093955.GW5388@noisy.programming.kicks-ass.net> References: <20250111042604.3230628-1-surenb@google.com> <20250111042604.3230628-11-surenb@google.com> <20250111063152.1638-1-hdanton@sina.com> <20250111121320.1656-1-hdanton@sina.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 9DB4D14000A X-Stat-Signature: cuxru59w8rktit794uq3e1caeeb5wdth X-HE-Tag: 1737024773-625565 X-HE-Meta: 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 lZKLByYl RuY1gHAFnJV6mA65OrqJ+Qrw7ca9UUi0JH6YZhWJv4lWTzBXn9+uYvB/HvDP1FASGxJcjGAV49nLkfcmaRhmAR5qqR6n0M0IAIXJ7cLmInkpRDnOEGChn5W71KErh6SWHREt8K8Iau7xxkxY2trNd72gJQ2v9JKfmCD/Dj/AAImXolpK3rWbBysqX42L6m4PmG1B9lYyDGEmgJJZYM2WczAFRG0gd2Jqh+sWn X-Bogosity: Ham, tests=bogofilter, spamicity=0.000010, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 15 Jan 2025 10:39:55 +0100 Peter Zijlstra > > Sigh; don't let hillf confuse you. *IF* you need an acquire it will be > in the part where you wait for readers to go away. But even there, think > about what you're serializing against. Readers don't typically modify > things. > > And modifications are fully serialized by mmap_sem^H^H^Hlock. > ^H^H^H - * Do note that inc_not_zero() provides a control dependency which will order - * future stores against the inc, this ensures we'll never modify the object - * if we did not in fact acquire a reference. + * Do note that inc_not_zero() does provide acquire order, which will order + * future load and stores against the inc, this ensures all subsequent accesses + * are from this object and not anything previously occupying this memory -- + * consider SLAB_TYPESAFE_BY_RCU. * * The decrements will provide release order, such that all the prior loads and * stores will be issued before, it also provides a control dependency, which @@ -144,7 +145,7 @@ bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp) do { if (!old) break; - } while (!atomic_try_cmpxchg_relaxed(&r->refs, &old, old + i)); + } while (!atomic_try_cmpxchg_acquire(&r->refs, &old, old + i));