From nobody Thu Apr 2 20:07:32 2026 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (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 D4D302F39D7 for ; Fri, 27 Mar 2026 02:15:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774577706; cv=none; b=JeScKIyTl0h0T5REu5xGQc6K9EHONMkz0ghwNKP+PhUUZKrLB5AlZRGZcDvmF4StK0Ois7F2MwJhmEk4OCz5zjSmrSIufmm7XspJyBh3EcAEwvT1EY4onP1gVLuccU4FJ3GfCxjiNz43G/1MGzr4n1bVxuq7YejzY2pAI3SI13w= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774577706; c=relaxed/simple; bh=s0WP9xhE1CTtNKRy6LtQcqflof/ya4sCmhE4hMDDEWI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=CI2YicaxrU25uNAJ6ay5jS4xj9xJS36FN8epKgqDq7CO6rP1C6C2lUYLbvg0HMZfhEWYW5nrv6y5SwIA3S7Q5GCxLapLLy6sBHTd8Xj7s0xWs4Sud87d6AH7UeRyXfY/CM4K09xAVJAZvESWz+TnpFG7OeyWgtovaKto+HSXB1U= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=c+UwEtgW; arc=none smtp.client-ip=91.218.175.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="c+UwEtgW" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1774577702; 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=giSfT9S4Y3Fs6MBCHHOkpgsjb4flU8mTLfNnlsB/wxU=; b=c+UwEtgWwyc5ExZqiso+pcfyt+iKbZ1QmoTTRB8NhGDZKpUwyzQzLx5Oi6hXFvtdq5ago3 ODRA0nas4eR1mjjEDHyY5MY9At3yhrqG1QJr6rpr5PRO3un578DMuu2R03YOspCxOxZ+jD EPix5NId6vnIBtCHcU6MJtVrfHvraLA= From: Usama Arif To: Andrew Morton , david@kernel.org, Lorenzo Stoakes , willy@infradead.org, linux-mm@kvack.org Cc: fvdl@google.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, npache@redhat.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, kernel-team@meta.com, maddy@linux.ibm.com, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, linux-s390@vger.kernel.org, Usama Arif Subject: [v3 08/24] mm: thp: handle split failure in follow_pmd_mask() Date: Thu, 26 Mar 2026 19:08:50 -0700 Message-ID: <20260327021403.214713-9-usama.arif@linux.dev> In-Reply-To: <20260327021403.214713-1-usama.arif@linux.dev> References: <20260327021403.214713-1-usama.arif@linux.dev> 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-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" follow_pmd_mask() splits a huge PMD when FOLL_SPLIT_PMD is set, so GUP can pin individual pages at PTE granularity. If the split fails, the PMD is still huge and follow_page_pte() cannot process it. Return ERR_PTR(-ENOMEM) on split failure, which causes the GUP caller to get -ENOMEM. -ENOMEM is already returned in follow_pmd_mask if pte_alloc_one fails (which is the reason why split_huge_pmd could fail), hence this is a safe change. Signed-off-by: Usama Arif --- mm/gup.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/gup.c b/mm/gup.c index ad9ded39609cb..07c6b0483c322 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -928,8 +928,16 @@ static struct page *follow_pmd_mask(struct vm_area_str= uct *vma, return follow_page_pte(vma, address, pmd, flags); } if (pmd_trans_huge(pmdval) && (flags & FOLL_SPLIT_PMD)) { + int ret; + spin_unlock(ptl); - split_huge_pmd(vma, pmd, address); + /* + * If split fails, the PMD is still huge and + * we cannot proceed to follow_page_pte. + */ + ret =3D split_huge_pmd(vma, pmd, address); + if (ret) + return ERR_PTR(ret); /* If pmd was left empty, stuff a page table in there quickly */ return pte_alloc(mm, pmd) ? ERR_PTR(-ENOMEM) : follow_page_pte(vma, address, pmd, flags); --=20 2.52.0