From nobody Sat Dec 27 15:11:27 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 413501429A for ; Tue, 19 Dec 2023 07:57:47 +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="Y5b7wywr" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1702972666; 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=7UtlH+qJqHqzo7Y62yc3egVvRJlUYI/8xtDdmttQSUc=; b=Y5b7wywrl16gpY3+tzbsVsuvPxD5fZXreYpvcGhI4HODV4jgYBqgD2MDW6GhvWJiEOdbc3 flgTQM1SNdI+rbNOjOc9rCpkh0EsCijIMtev+gG9mcLn2HnW+NZ4w1SSYyaR5XJfadxxHE KRe6IX2k5lPo69getGFoq8tln6Qpocg= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-197-HHPXr_gTMGKJxc1F8Y3Vvw-1; Tue, 19 Dec 2023 02:57:42 -0500 X-MC-Unique: HHPXr_gTMGKJxc1F8Y3Vvw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (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 13EAF1C0513F; Tue, 19 Dec 2023 07:57:41 +0000 (UTC) Received: from x1n.redhat.com (unknown [10.72.116.117]) by smtp.corp.redhat.com (Postfix) with ESMTP id D699F2026D66; Tue, 19 Dec 2023 07:57:28 +0000 (UTC) From: peterx@redhat.com To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Matthew Wilcox , Christophe Leroy , Lorenzo Stoakes , David Hildenbrand , Vlastimil Babka , Mike Kravetz , Mike Rapoport , Christoph Hellwig , John Hubbard , Andrew Jones , linux-arm-kernel@lists.infradead.org, Michael Ellerman , "Kirill A . Shutemov" , linuxppc-dev@lists.ozlabs.org, Rik van Riel , linux-riscv@lists.infradead.org, Yang Shi , James Houghton , "Aneesh Kumar K . V" , Andrew Morton , Jason Gunthorpe , Andrea Arcangeli , peterx@redhat.com, Axel Rasmussen Subject: [PATCH 09/13] mm/gup: Cache *pudp in follow_pud_mask() Date: Tue, 19 Dec 2023 15:55:34 +0800 Message-ID: <20231219075538.414708-10-peterx@redhat.com> In-Reply-To: <20231219075538.414708-1-peterx@redhat.com> References: <20231219075538.414708-1-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 10.11.54.4 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. Signed-off-by: Peter Xu Acked-by: James Houghton --- mm/gup.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 6c0d82fa8cc7..97e87b7a15c3 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 *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