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 6369DCA1017 for ; Thu, 4 Sep 2025 06:47:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BB0F48E0012; Thu, 4 Sep 2025 02:47:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B87108E0002; Thu, 4 Sep 2025 02:47:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A9CE48E0012; Thu, 4 Sep 2025 02:47:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 97D578E0002 for ; Thu, 4 Sep 2025 02:47:07 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 42A0C11ACE9 for ; Thu, 4 Sep 2025 06:47:07 +0000 (UTC) X-FDA: 83850635694.12.B4DF85E Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) by imf22.hostedemail.com (Postfix) with ESMTP id 9010BC000B for ; Thu, 4 Sep 2025 06:47:05 +0000 (UTC) Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=WzA82SHo ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1756968425; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=efyhR8wHhw8uesblYSnLgPQBPUNCW7rCVpcxJ83V5M0=; b=QCTfblU+i0gAa1Ix4B02lMc0PdpmL2cI+l99YY0NWmjhjbse2t0nrrtw6390XJjcvigmMR 1OJSPMMswCfHQNKR2zb63fSO/Xt0zUa8WqvNmyUY+8m88UKMVbkT6KTDzVDF+xxYuVGDt8 1ueJkaGuWMDk8okbx42MYHPul4b9E/c= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1756968425; a=rsa-sha256; cv=none; b=arx3uMrfuACQ16/SDMWboj0b1PxQOfwGPkuAPZF5TMJNUOLD5CDJ3Hxxxmqs6LFzAI8L6s zgAQPYd55Ts1JGjJBUPxqHM7333mOhRRfL64ur1VIn/2RTsyK7oRbt1lFHGT2C/NI0E9Cu 0VPjSFCMHNg43x3lko/sxSifnhZCf0I= ARC-Authentication-Results: i=1; imf22.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=WzA82SHo; spf=none (imf22.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=efyhR8wHhw8uesblYSnLgPQBPUNCW7rCVpcxJ83V5M0=; b=WzA82SHoMRi9yVKB7fE7LAuc1c jsspskezLL1ajqArYYKzI6cX4WAwNcIkBBMtuGNUrV7io6kKfesya8FJMYYysXDzhT5ImjOLY6LFV 248MTKZQHUNmlfu2GDFS/rdAZg0ZwzLMpkBnhkCCu548qhVx0yqSkFrCciRhTe05ZA4D36cQAIgAF uSGincVkuMSsYe6AEzciEecgQynn8iCwaWTJrIk4o8qLMnj04bDec49lcxdEb4sUGgOY8xHaRUya2 SrO/LvCDU13jdZ3xoZf3iSRb8Uw1HdzRWYccGJKRwrny/suwG+mF2+B1WfIwU77Mz+0C+q3L0/MR+ dw+7hO0w==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uu3kK-00000004IX4-0HP9; Thu, 04 Sep 2025 06:47:00 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 91B3F3002BF; Thu, 04 Sep 2025 08:46:59 +0200 (CEST) Date: Thu, 4 Sep 2025 08:46:59 +0200 From: Peter Zijlstra To: Jinchao Wang Cc: Andrew Morton , Masami Hiramatsu , "Naveen N . Rao" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , "Liang, Kan" , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-perf-users@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 07/18] mm/ksw: add atomic watch on/off operations Message-ID: <20250904064659.GV4067720@noisy.programming.kicks-ass.net> References: <20250904002126.1514566-1-wangjinchao600@gmail.com> <20250904002126.1514566-8-wangjinchao600@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250904002126.1514566-8-wangjinchao600@gmail.com> X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 9010BC000B X-Stat-Signature: fsxku78ha44qjo8pxuumrqztsaq31njz X-Rspam-User: X-HE-Tag: 1756968425-10770 X-HE-Meta: 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 uman4xOK 3gdnAW+mvHv8RWudiOAqqtKcqkIiLvTMJQT7XcgUnm09/40SxbaBFPSSp2CL25vMpuVqoSARfJqcI2xUfpVMvaCDbSPFHi1Hx9pVYDoNz2aYjgtJ5S0pjGN4v9pkmDSPsdiCVhIaXnEne3ao= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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 Thu, Sep 04, 2025 at 08:21:04AM +0800, Jinchao Wang wrote: > +static DEFINE_PER_CPU(call_single_data_t, > + watch_csd) = CSD_INIT(ksw_watch_on_local_cpu, > + &watch_info); > + > +int ksw_watch_on(u64 watch_addr, u64 watch_len) > +{ > + unsigned long flags; > + int cpu; > + > + if (!watch_addr) { > + pr_err("KSW: watch with invalid address\n"); > + return -EINVAL; > + } > + > + spin_lock_irqsave(&watch_lock, flags); > + > + /* > + * check if already watched > + */ > + if (watch_info.addr != 0 && // not uninit > + watch_info.addr != (unsigned long)&watch_holder && // installed > + watch_addr != (unsigned long)&watch_holder) { //not restore > + spin_unlock_irqrestore(&watch_lock, flags); > + return -EBUSY; > + } > + > + watch_info.addr = watch_addr; > + watch_info.len = watch_len; > + > + spin_unlock_irqrestore(&watch_lock, flags); > + > + if (watch_addr == (unsigned long)&watch_holder) > + pr_debug("KSW: watch off starting\n"); > + else > + pr_debug("KSW: watch on starting\n"); > + > + for_each_online_cpu(cpu) { > + if (cpu == raw_smp_processor_id()) { > + ksw_watch_on_local_cpu(&watch_info); > + } else { > + call_single_data_t *csd = &per_cpu(watch_csd, cpu); > + > + smp_call_function_single_async(cpu, csd); > + } > + } > + > + return 0; > +} What do you think happens when two ksw_watch_on() instances run concurrently? What happens if a CPU comes online/offline concurrently with ksw_watch_on()?