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 EC860EB64D7 for ; Fri, 23 Jun 2023 10:54:02 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 881808D0002; Fri, 23 Jun 2023 06:54:02 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 831B88D0001; Fri, 23 Jun 2023 06:54:02 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6F9778D0002; Fri, 23 Jun 2023 06:54:02 -0400 (EDT) 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 59EE38D0001 for ; Fri, 23 Jun 2023 06:54:02 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 1622B1C9376 for ; Fri, 23 Jun 2023 10:54:02 +0000 (UTC) X-FDA: 80933702724.23.F478E59 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf05.hostedemail.com (Postfix) with ESMTP id 1893E100011 for ; Fri, 23 Jun 2023 10:53:59 +0000 (UTC) Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=VaueObhM; spf=pass (imf05.hostedemail.com: domain of pmladek@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=pmladek@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1687517640; 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=BvyCNbBz5JrR/Syp0f3tWO61NEyonBUXQOe30F+oRQw=; b=ZlrMDLOLfXAvv/3VLtIuGMgkvwXYOKkKaANF3EpqNDII1mHST+R6xOGndpPlYzCY3DZSpk ue/nXDUcZgPI8lUlXs1ktEiBOv+LhGwpryy3joSNqWNiK/rX/nVcYHKbTHp03cKYh2c4Ux H07J7PYnr8mb1DqJr5R3fuz/GOZ7ae4= ARC-Authentication-Results: i=1; imf05.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=VaueObhM; spf=pass (imf05.hostedemail.com: domain of pmladek@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=pmladek@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1687517640; a=rsa-sha256; cv=none; b=zvz52vguUvlj3hQrmli1TgiN5WvOF42XgJyh1BFPP+X0dfAA8ne1hoEwtFpDuc9toCDGI0 2YOXDYPnSKHsRgpYCIIRkDF/mAYX3/TDwTTjkV7czdIW298rmHrUVQ0rULaNxP9gamBojb 2WYBjvD3soPys0L+7oc/5lzxRQmPYmc= Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 89B2F21B08; Fri, 23 Jun 2023 10:53:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1687517638; h=from:from:reply-to: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=BvyCNbBz5JrR/Syp0f3tWO61NEyonBUXQOe30F+oRQw=; b=VaueObhMHiaSTnv5F3cGLXiUaDd/IOKyCr3lQcb1Euu/Ks1nzmdAt9jDh3ZFKCAL+rHbTk BZOD5gu11ResoO8jZRE6Lsi8YpnywGbrQ4k7BwQmVscTmem/q8DVxyzkqLPR1oJgnT0fOM cmH3qF0GDMvcMMOPUTQBjFSeXjz54Bo= Received: from suse.cz (unknown [10.100.201.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 4D2D92C141; Fri, 23 Jun 2023 10:53:58 +0000 (UTC) Date: Fri, 23 Jun 2023 12:53:57 +0200 From: Petr Mladek To: Sebastian Andrzej Siewior Cc: Tetsuo Handa , linux-mm@kvack.org, "Luis Claudio R. Goncalves" , Andrew Morton , Mel Gorman , Michal Hocko , Thomas Gleixner Subject: Re: [PATCH] mm/page_alloc: Use write_seqlock_irqsave() instead write_seqlock() + local_irq_save(). Message-ID: References: <20230621143421.BgHjJklo@linutronix.de> <01031ffe-c81f-9cec-76fb-e70d548429cf@I-love.SAKURA.ne.jp> <8b6d3f39-c573-ca2b-957b-8c48c2fa68ad@I-love.SAKURA.ne.jp> <20230623094544.RcLNdg6H@linutronix.de> <20230623101111.7tuAg5p5@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230623101111.7tuAg5p5@linutronix.de> X-Rspamd-Queue-Id: 1893E100011 X-Rspam-User: X-Stat-Signature: rqc6nyhoq9ikyrgtckp7s3mcywwnpwxp X-Rspamd-Server: rspam01 X-HE-Tag: 1687517639-456410 X-HE-Meta: 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 iqZ31Cr7 Rn7PHBQQOMY5zYlONbNnC8o/PmiNK+DRe+rK6Aw6kyR6lND8TjD3somzmJqTn//+42JT/QHU9WOnqzmBxk46rMtYFz1t2dy/0NekoG8AgAEBdrXYJfRKXC3ySX9eDHc46ITLivJHnaCjhidqiHwnK2rDt4r+v0s3OzIfb8HIUu/nErMvlzpgyXARJS2niBIB9rIKF 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: On Fri 2023-06-23 12:11:11, Sebastian Andrzej Siewior wrote: > On 2023-06-23 18:51:24 [+0900], Tetsuo Handa wrote: > > My understanding is that zonelist_iter_begin() accesses only zonelist_update_seq.seqcount . > > From where is the zonelist_update_seq.lock accessed when zonelist_iter_begin() is called? > > zonelist_iter_begin() > -> read_seqbegin() > -> read_seqcount_begin() > -> raw_read_seqcount_begin() > -> __read_seqcount_begin() > > Now. The inner part looks like > while ((__seq = seqprop_sequence(s)) & 1) > cpu_relax(); > > but with RT enabled (in-tree, not out-of-tree, in-tree) seqprop_sequence() > goes from: BTW: I see a possible race in the below code. > | unsigned __seqprop_spinlock_sequence(const seqcount_spinlock_t *s) > | { > | unsigned seq = READ_ONCE(s->seqcount.sequence); > | > | if (unlikely(seq & 1)) { > | spin_lock(s->lock); > | spin_unlock(s->lock); This guarantees the reader waits for the writer. But does this guarantee that another writer could not bump the sequence before we read it below? > | seq = READ_ONCE(s->seqcount.sequence); IMHO, it should be: if (unlikely(seq & 1)) { spin_lock(s->lock); seq = READ_ONCE(s->seqcount.sequence); spin_unlock(s->lock); IMHO, only this would guarantee that returned seq couldn't be odd. Best Regards, Petr > | } > | return seq; > | }