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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 11124EEF30F for ; Thu, 5 Mar 2026 07:01:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5B7336B0088; Thu, 5 Mar 2026 02:01:56 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 58EE76B0089; Thu, 5 Mar 2026 02:01:56 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 491356B008A; Thu, 5 Mar 2026 02:01:56 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 373C66B0088 for ; Thu, 5 Mar 2026 02:01:56 -0500 (EST) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id CC4E513BC0B for ; Thu, 5 Mar 2026 07:01:55 +0000 (UTC) X-FDA: 84511114590.20.ED3A92B Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) by imf27.hostedemail.com (Postfix) with ESMTP id D21D040008 for ; Thu, 5 Mar 2026 07:01:48 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; spf=pass (imf27.hostedemail.com: domain of chenridong@huaweicloud.com designates 45.249.212.56 as permitted sender) smtp.mailfrom=chenridong@huaweicloud.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1772694114; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=baI6LYxj5wn1XSeNwcLBlxFC0lZboab4d9n05IAF6uA=; b=gmnm9K/CcP5lncZt6NEUv3B8c2tV6ugjFXB7jrJeDg6YKG6wuHvvV67uHhOJQg1GSUP6sF Ck7MsMEL1SGxPY/UyxCmq+UHI6ajGJWHSoUcsErjqKLjySEXami/rJ3Yrx7XMYstlgmhW1 0fhXSMl/YrECwctQ7Vxc/fkOCemE11c= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772694114; a=rsa-sha256; cv=none; b=vNlZ8XEL46xGWNX1lNeQ+h5ZkyUYGmYNAQD6ir8sLqITFJFubXPdvxVUWPKfQBwnwY+woc 7VRmUsRVbJsTI2e5/RizdjfroYCfws30n9UE1wAJqQFcFh8GP+Tdn8kZyZxcVqBNbfM7xx J3pTQ2+EKiJ1dnOiUIxN7OJC9Ec/+yE= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf27.hostedemail.com: domain of chenridong@huaweicloud.com designates 45.249.212.56 as permitted sender) smtp.mailfrom=chenridong@huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.163.198]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4fRL750wplzKHMTt for ; Thu, 5 Mar 2026 15:01:37 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 3BC3C40539 for ; Thu, 5 Mar 2026 15:01:44 +0800 (CST) Received: from [10.67.111.176] (unknown [10.67.111.176]) by APP4 (Coremail) with SMTP id gCh0CgCXQ_RWKqlpLaSPJg--.31504S2; Thu, 05 Mar 2026 15:01:44 +0800 (CST) Message-ID: <7018d437-a132-4a26-9c46-e61c96775fb4@huaweicloud.com> Date: Thu, 5 Mar 2026 15:01:42 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/3] cgroup: add lockless fast-path checks to cgroup_file_notify() To: Shakeel Butt Cc: Tejun Heo , Johannes Weiner , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Roman Gushchin , Kuniyuki Iwashima , Daniel Sedlak , Meta kernel team , linux-mm@kvack.org, netdev@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Jakub Kicinski References: <20260228142018.3178529-1-shakeel.butt@linux.dev> <20260228142018.3178529-3-shakeel.butt@linux.dev> <40c77bba-0862-4422-b23e-2a10cd01c728@huaweicloud.com> <372e0d67-ab3f-427f-970d-5d1c7cb68c92@huaweicloud.com> Content-Language: en-US From: Chen Ridong In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CM-TRANSID:gCh0CgCXQ_RWKqlpLaSPJg--.31504S2 X-Coremail-Antispam: 1UD129KBjvJXoW7uw1rXr43tw48Gw17WFW8Xrb_yoW8Gry5pa yqy3Zaka1qgrWYgr109as0q3sY934xtF47ZFW0vryktrZrZFyftF47AF1UuF47ArZ7G3yx Zr1Yqr9xC398Aa7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUv0b4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7MxkF7I0En4kS 14v26r1q6r43MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I 8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8 ZwCIc40Y0x0EwIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x 0267AKxVW8JVWxJwCI42IY6xAIw20EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_ Jr0_Gr1lIxAIcVC2z280aVCY1x0267AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7IU1 7KsUUUUUU== X-CM-SenderInfo: hfkh02xlgr0w46kxt4xhlfz01xgou0bp/ X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D21D040008 X-Stat-Signature: 13hh99dfund4iqofwmx5bj7n4q8ymmjf X-Rspam-User: X-HE-Tag: 1772694108-103297 X-HE-Meta: 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 Z2Qe7w02 +Oa7Eh/WqzXudn70oeNBquGqMH+G6bDRwmoXAG+r8vEYIIRgSQZfSK17xGH8+KpYzBOZH7E3R37sqzU+gqmfciHBRSAlVBJlabs13jN9LYOvQElxHk6Rdmgm0llk/XzjT9MUy02oD9jc1YryvoDEd0tsqklXn8ZueL6S24JXQGwS3ppo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/3/3 12:01, Shakeel Butt wrote: > On Tue, Mar 03, 2026 at 11:18:17AM +0800, Chen Ridong wrote: >> >> > [...] >>> @@ -4689,6 +4689,12 @@ void cgroup_file_notify(struct cgroup_file *cfile) >>> unsigned long flags; >>> struct kernfs_node *kn = NULL; >>> >>> + if (!READ_ONCE(cfile->kn)) >>> + return; >>> + >>> + if (timer_pending(&cfile->notify_timer)) >>> + return; >>> + >> >> The added timer_pending() check seems problematic. According to the function's >> comment, callers must ensure serialization with other timer operations. Here >> we're checking timer_pending() locklessly, which means we might: >> > > That comment seems outdated. Check the commit 90c018942c2ba ("timer: Use > hlist_unhashed_lockless() in timer_pending()"). > Maybe we should update the comment. >> 1. See an inconsistent state if another CPU is concurrently modifying the timer >> > > It will not see inconsistent state but it can see stale state which is totally > fine. At worst we will take the lock and recheck but we will never miss the > notifications. > You are right. Thank you for explanation. >> 2. Race with del_timer() or mod_timer() from other contexts >> >>> spin_lock_irqsave(&cgroup_file_kn_lock, flags); >>> if (cfile->kn) { >>> unsigned long last = cfile->notified_at; >> >> -- >> Best regards, >> Ridong >> -- Best regards, Ridong