From nobody Mon Dec 15 23:00:43 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D180819BCC for ; Wed, 3 Jan 2024 09:16:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="du7VdgO4" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704273392; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dkbsR+hObgkKanb0hWK1+Xo39A1xL8364xJAXCv3uQU=; b=du7VdgO4cxnkmxRWxbfQ1qq5y/m7KFtTHooajSvIdqWs4PL53aO4HuDgOJnsj/wXWQYfEc iPTHK9VOOxXN1ugLPw0RtIHGNSRvnbxnfij7aanlWwtyi+gU6britB/c/FD2UWVPmpDJym mXFRAfMTYQuE3lEg/2LVbTrSxRRiYhE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-611-7CEiuF6PMvSSKuTScRXfJw-1; Wed, 03 Jan 2024 04:16:28 -0500 X-MC-Unique: 7CEiuF6PMvSSKuTScRXfJw-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 8EF2A185A780; Wed, 3 Jan 2024 09:16:27 +0000 (UTC) Received: from x1n.redhat.com (unknown [10.72.116.69]) by smtp.corp.redhat.com (Postfix) with ESMTP id 33861492BE6; Wed, 3 Jan 2024 09:16:15 +0000 (UTC) From: peterx@redhat.com To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: James Houghton , David Hildenbrand , "Kirill A . Shutemov" , Yang Shi , peterx@redhat.com, linux-riscv@lists.infradead.org, Andrew Morton , "Aneesh Kumar K . V" , Rik van Riel , Andrea Arcangeli , Axel Rasmussen , Mike Rapoport , John Hubbard , Vlastimil Babka , Michael Ellerman , Christophe Leroy , Andrew Jones , linuxppc-dev@lists.ozlabs.org, Mike Kravetz , Muchun Song , linux-arm-kernel@lists.infradead.org, Jason Gunthorpe , Christoph Hellwig , Lorenzo Stoakes , Matthew Wilcox Subject: [PATCH v2 09/13] mm/gup: Cache *pudp in follow_pud_mask() Date: Wed, 3 Jan 2024 17:14:19 +0800 Message-ID: <20240103091423.400294-10-peterx@redhat.com> In-Reply-To: <20240103091423.400294-1-peterx@redhat.com> References: <20240103091423.400294-1-peterx@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.10 Content-Type: text/plain; charset="utf-8" From: Peter Xu Introduce "pud_t pud" in the function, so the code won't dereference *pudp multiple time. Not only because that looks less straightforward, but also because if the dereference really happened, it's not clear whether there can be race to see different *pudp values if it's being modified at the same time. Acked-by: James Houghton Signed-off-by: Peter Xu Reviewed-by: Jason Gunthorpe --- mm/gup.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index b8a80e2bfe08..63845b3ec44f 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -753,26 +753,27 @@ static struct page *follow_pud_mask(struct vm_area_st= ruct *vma, unsigned int flags, struct follow_page_context *ctx) { - pud_t *pud; + pud_t *pudp, pud; spinlock_t *ptl; struct page *page; struct mm_struct *mm =3D vma->vm_mm; =20 - pud =3D pud_offset(p4dp, address); - if (pud_none(*pud)) + pudp =3D pud_offset(p4dp, address); + pud =3D READ_ONCE(*pudp); + if (pud_none(pud)) return no_page_table(vma, flags, address); - if (pud_devmap(*pud)) { - ptl =3D pud_lock(mm, pud); - page =3D follow_devmap_pud(vma, address, pud, flags, &ctx->pgmap); + if (pud_devmap(pud)) { + ptl =3D pud_lock(mm, pudp); + page =3D follow_devmap_pud(vma, address, pudp, flags, &ctx->pgmap); spin_unlock(ptl); if (page) return page; return no_page_table(vma, flags, address); } - if (unlikely(pud_bad(*pud))) + if (unlikely(pud_bad(pud))) return no_page_table(vma, flags, address); =20 - return follow_pmd_mask(vma, address, pud, flags, ctx); + return follow_pmd_mask(vma, address, pudp, flags, ctx); } =20 static struct page *follow_p4d_mask(struct vm_area_struct *vma, --=20 2.41.0