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=-9.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 16E2FC5B578 for ; Mon, 1 Jul 2019 06:20:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C0FB52146E for ; Mon, 1 Jul 2019 06:20:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="gSbk2W6E" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C0FB52146E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 907C38E0007; Mon, 1 Jul 2019 02:20:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 892516B000C; Mon, 1 Jul 2019 02:20:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6E3C68E0007; Mon, 1 Jul 2019 02:20:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-pl1-f208.google.com (mail-pl1-f208.google.com [209.85.214.208]) by kanga.kvack.org (Postfix) with ESMTP id 1DB676B0008 for ; Mon, 1 Jul 2019 02:20:47 -0400 (EDT) Received: by mail-pl1-f208.google.com with SMTP id u10so6739188plq.21 for ; Sun, 30 Jun 2019 23:20:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:dkim-signature:from:to:cc:subject:date :message-id:in-reply-to:references:mime-version :content-transfer-encoding; bh=APKBQWkk9iHwyQHEt2C0MEBOgtO6KbM8T5bZXthkZZI=; b=ZaoL+buQGrZ/Q9DjMqwd1TI/6MPpgrMVHI1Lb31Cbx3XobM2Oiw76AgrmHdk8qH2Gn aQWbRptWavdOnIcrtqiTmJPgDE9Mo9kveoXAVe0htC57Uj85ZRI0p9MYlurKI/vpA8qH HzNh1kodYmggBUMRw0W/mYZiUfonrr+XkQV+02HOpNJxMUpQr4NR/+/BTpXcDJfwDiVn +lfEK+2p0wa7wiFTrO+7ow0HN5LYeeGNhqyuPfqJyb3gRQLyHoMCHDklXvd5mU1HHKCM vbPgsKKyEkaG7oC/GVfPs8LjCoCJy5qrVOTUY4NWdFf1CSyWTXKmJ7WyYoYvRh6We6Zk 3Pbg== X-Gm-Message-State: APjAAAVAhRGm0ne3I6KPKC8DMlcbBTkELhs2jW+ukzAWYJqtebH4nEE5 jjk1TH+y7klkFxu5WP+ETCgicpozlcXGPzVVTKuZrTIVY+0TPeLj1GhANTkqcAzTPN1OxFMyDcQ gy6cscZI/OstzzVu2nhOOlvikDFNSyy9a5NqLPIxlNF8Nwx7jyucnXazJHN/21R4= X-Received: by 2002:a65:43cd:: with SMTP id n13mr23783214pgp.208.1561962046615; Sun, 30 Jun 2019 23:20:46 -0700 (PDT) X-Google-Smtp-Source: APXvYqyUY5uuQWc8z+K8+kTs/nbafTmOr6qFDb4bGgBY39wNSIZ/40pP8VJUn7IaWt6AKyN0dG5b X-Received: by 2002:a65:43cd:: with SMTP id n13mr23783155pgp.208.1561962045731; Sun, 30 Jun 2019 23:20:45 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1561962045; cv=none; d=google.com; s=arc-20160816; b=NUbDcQ2VVb+8ty/2VFNWBskgaSALho+8ZRy3WXFwKS1utLVifkw9VUSMsyj6+SBkAF SGO0Z2GzzggAK8QVSeC0HYtgiYfEI5eDfjtgrc0aoaCgz9xy25KSa5GGBMM99dry/bAT OJC2xPzfF1n/Ce9vhBN9iIXZoFkolazEYNzv8SrafSZvY1eSANaAc0cMMUn2E95F6sit dilrAOgY3xsxl+Y/e2bziWnNVrKbSL6Hj7MYRM3Hydld7+jl0caGYsaAr3R3Km49OOlZ DnpPUscXL7NhFtFEZvqu24FgUgQOVruBYoGrharCMS1ATGAeVxaCCXopQF2D6Ym3TelP 5pZw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:dkim-signature; bh=APKBQWkk9iHwyQHEt2C0MEBOgtO6KbM8T5bZXthkZZI=; b=0RJEE67zHyw5/0lYKgMbONXNFfryUtBBXlbMrPIf12o+JW+478Er/0TjmcH/UupEUr kFKkA/qytkIwsLMUrmm6hbNhExub0TBwSwdeltz7KMaNQ7DW7biRLkPVYhnIqK2hqTES uWByccEG5hOSkvIXEFkmXG0OX8zCVarJJotsTAZ4XM+b6V9E5oQjFaU+BYBR8hv2pIeR ebezzmjIzO7v/ESE/T42Me6tMz0G6yLTuUXZuTZ0WsGPk1ySaYnj1GXzKlcR1f1KSmNs X+5hgPqN7fg0xB+4q3I89SAI5GYihzF/B0qI8U5X6X5tuBIRLcfx/9qTGE2lv3Q6HUNd lLvw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=gSbk2W6E; spf=pass (google.com: best guess record for domain of batv+bb02ddf78a79a38d855c+5790+infradead.org+hch@bombadil.srs.infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=BATV+bb02ddf78a79a38d855c+5790+infradead.org+hch@bombadil.srs.infradead.org Received: from bombadil.infradead.org (bombadil.infradead.org. [2607:7c80:54:e::133]) by mx.google.com with ESMTPS id c7si5400871pjo.88.2019.06.30.23.20.45 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sun, 30 Jun 2019 23:20:45 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of batv+bb02ddf78a79a38d855c+5790+infradead.org+hch@bombadil.srs.infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=gSbk2W6E; spf=pass (google.com: best guess record for domain of batv+bb02ddf78a79a38d855c+5790+infradead.org+hch@bombadil.srs.infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=BATV+bb02ddf78a79a38d855c+5790+infradead.org+hch@bombadil.srs.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender :Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From :Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=APKBQWkk9iHwyQHEt2C0MEBOgtO6KbM8T5bZXthkZZI=; b=gSbk2W6E84lf5FtDNmA7UbJzV8 /YpjENtceLBi7lcdSkKI3hddigiEEfPq448QumXbzCmOvF+HQ4eGiOVwzgEgTxo59mprNYGLlbRal pFad60P91vtTjcQCJM33sMokpMT0eR115j8oJP1AFdexcCZJzIE+KPqTW59nqSqC58f1njztm+KLt nDzWjqQ54DQdSWM+FGXGX7f9sA7DlL6G91SyOHzqRMJtGs2Vw3Ec9RA8nXlpy5RPimyAnOMxTBWv8 scgz4P+mEmSq7QkjP1YKS3IDhkGZzrRmUCpak5IqWHEFnT7ZLMR6eXSwhpA9HpzzWOMtkhjLVW6wl FwufaIVQ==; Received: from [46.140.178.35] (helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hhpgA-0002y7-L6; Mon, 01 Jul 2019 06:20:43 +0000 From: Christoph Hellwig To: Dan Williams , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Jason Gunthorpe , Ben Skeggs Cc: Ira Weiny , linux-mm@kvack.org, nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-nvdimm@lists.01.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, John Hubbard , Ralph Campbell , Philip Yang Subject: [PATCH 09/22] mm/hmm: Simplify hmm_get_or_create and make it reliable Date: Mon, 1 Jul 2019 08:20:07 +0200 Message-Id: <20190701062020.19239-10-hch@lst.de> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190701062020.19239-1-hch@lst.de> References: <20190701062020.19239-1-hch@lst.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html 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: From: Jason Gunthorpe As coded this function can false-fail in various racy situations. Make it reliable and simpler by running under the write side of the mmap_sem and avoiding the false-failing compare/exchange pattern. Due to the mmap_sem this no longer has to avoid racing with a 2nd parallel hmm_get_or_create(). Unfortunately this still has to use the page_table_lock as the non-sleeping lock protecting mm->hmm, since the contexts where we free the hmm are incompatible with mmap_sem. Signed-off-by: Jason Gunthorpe Reviewed-by: John Hubbard Reviewed-by: Ralph Campbell Reviewed-by: Ira Weiny Reviewed-by: Christoph Hellwig Tested-by: Philip Yang --- mm/hmm.c | 77 ++++++++++++++++++++++---------------------------------- 1 file changed, 30 insertions(+), 47 deletions(-) diff --git a/mm/hmm.c b/mm/hmm.c index 080b17a2e87e..0423f4ca3a7e 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -31,16 +31,6 @@ #if IS_ENABLED(CONFIG_HMM_MIRROR) static const struct mmu_notifier_ops hmm_mmu_notifier_ops; -static inline struct hmm *mm_get_hmm(struct mm_struct *mm) -{ - struct hmm *hmm = READ_ONCE(mm->hmm); - - if (hmm && kref_get_unless_zero(&hmm->kref)) - return hmm; - - return NULL; -} - /** * hmm_get_or_create - register HMM against an mm (HMM internal) * @@ -55,11 +45,16 @@ static inline struct hmm *mm_get_hmm(struct mm_struct *mm) */ static struct hmm *hmm_get_or_create(struct mm_struct *mm) { - struct hmm *hmm = mm_get_hmm(mm); - bool cleanup = false; + struct hmm *hmm; + + lockdep_assert_held_exclusive(&mm->mmap_sem); - if (hmm) - return hmm; + /* Abuse the page_table_lock to also protect mm->hmm. */ + spin_lock(&mm->page_table_lock); + hmm = mm->hmm; + if (mm->hmm && kref_get_unless_zero(&mm->hmm->kref)) + goto out_unlock; + spin_unlock(&mm->page_table_lock); hmm = kmalloc(sizeof(*hmm), GFP_KERNEL); if (!hmm) @@ -74,57 +69,45 @@ static struct hmm *hmm_get_or_create(struct mm_struct *mm) hmm->notifiers = 0; hmm->dead = false; hmm->mm = mm; - mmgrab(hmm->mm); - spin_lock(&mm->page_table_lock); - if (!mm->hmm) - mm->hmm = hmm; - else - cleanup = true; - spin_unlock(&mm->page_table_lock); + hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops; + if (__mmu_notifier_register(&hmm->mmu_notifier, mm)) { + kfree(hmm); + return NULL; + } - if (cleanup) - goto error; + mmgrab(hmm->mm); /* - * We should only get here if hold the mmap_sem in write mode ie on - * registration of first mirror through hmm_mirror_register() + * We hold the exclusive mmap_sem here so we know that mm->hmm is + * still NULL or 0 kref, and is safe to update. */ - hmm->mmu_notifier.ops = &hmm_mmu_notifier_ops; - if (__mmu_notifier_register(&hmm->mmu_notifier, mm)) - goto error_mm; - - return hmm; - -error_mm: spin_lock(&mm->page_table_lock); - if (mm->hmm == hmm) - mm->hmm = NULL; + mm->hmm = hmm; + +out_unlock: spin_unlock(&mm->page_table_lock); -error: - mmdrop(hmm->mm); - kfree(hmm); - return NULL; + return hmm; } static void hmm_free_rcu(struct rcu_head *rcu) { - kfree(container_of(rcu, struct hmm, rcu)); + struct hmm *hmm = container_of(rcu, struct hmm, rcu); + + mmdrop(hmm->mm); + kfree(hmm); } static void hmm_free(struct kref *kref) { struct hmm *hmm = container_of(kref, struct hmm, kref); - struct mm_struct *mm = hmm->mm; - mmu_notifier_unregister_no_release(&hmm->mmu_notifier, mm); + spin_lock(&hmm->mm->page_table_lock); + if (hmm->mm->hmm == hmm) + hmm->mm->hmm = NULL; + spin_unlock(&hmm->mm->page_table_lock); - spin_lock(&mm->page_table_lock); - if (mm->hmm == hmm) - mm->hmm = NULL; - spin_unlock(&mm->page_table_lock); - - mmdrop(hmm->mm); + mmu_notifier_unregister_no_release(&hmm->mmu_notifier, hmm->mm); mmu_notifier_call_srcu(&hmm->rcu, hmm_free_rcu); } -- 2.20.1