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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DD8F110AB83C for ; Fri, 27 Mar 2026 02:15:47 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 532F36B00B9; Thu, 26 Mar 2026 22:15:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 50A246B00BB; Thu, 26 Mar 2026 22:15:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 447726B00BC; Thu, 26 Mar 2026 22:15:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 3545F6B00B9 for ; Thu, 26 Mar 2026 22:15:47 -0400 (EDT) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 01B8C13C2B7 for ; Fri, 27 Mar 2026 02:15:46 +0000 (UTC) X-FDA: 84590227134.03.1EE051D Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) by imf06.hostedemail.com (Postfix) with ESMTP id 5870F18000C for ; Fri, 27 Mar 2026 02:15:45 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=Hnot0p5K; spf=pass (imf06.hostedemail.com: domain of usama.arif@linux.dev designates 91.218.175.172 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1774577745; a=rsa-sha256; cv=none; b=tuvcj1mK36jMIyr3wI0N8yiGczRlqjeki4AP+titdu5iNxGNuS04MMH1YvdYTgbuTwGDx5 /rReg6ODqGd72pHGPi9bUgtNPN2nSB76n3kssnw4Bt980hjUU9wkKXO3pFYgAavyZ5RdKu zUeZf2CtmUNI/qEJbghRN05Me+IH5sk= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1774577745; 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-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=8tx/Qjve1iVx/sjsNymGDpKKmMZv1TUyDs/EfcYY5GE=; b=Rg302JzgrlplHou1tNHLCYrwRkHPdOMWBC3Zk/8fcwLTKNDJmQF4LgxovghA5KiVR/MeWw TUKjizYN3E30f4+aVr2+zR/wpSp8DcPwjb3fwKflRGrIf23hDGcbrOLCzO5cByRq+dwEM5 fTdWSD4OBhL+aAjDhbOViguy88txRTc= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=Hnot0p5K; spf=pass (imf06.hostedemail.com: domain of usama.arif@linux.dev designates 91.218.175.172 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev 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=1774577743; 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=8tx/Qjve1iVx/sjsNymGDpKKmMZv1TUyDs/EfcYY5GE=; b=Hnot0p5K89CAv1AQSFPCVNypjXRfAocNMIZyWJnznY4gpq+GWy2CVy+0V7yyIEu0F+HuLG VCDbIV/SqybnVZSHtV9JQkcdTWMzMp9IQ8Hs+qWemVt0yevh5Dk4OIgO/2Wqfo3fp+W2Sb aJvabR1V9LfLrBzcx+XgaoHKYXMXuJs= 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 15/24] fs/dax: handle split_huge_pmd failure in dax_iomap_pmd_fault Date: Thu, 26 Mar 2026 19:08:57 -0700 Message-ID: <20260327021403.214713-16-usama.arif@linux.dev> In-Reply-To: <20260327021403.214713-1-usama.arif@linux.dev> References: <20260327021403.214713-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 5870F18000C X-Stat-Signature: jtzixah4ikmagqur9f8i5y365zjm8o4c X-HE-Tag: 1774577745-766645 X-HE-Meta: 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 nnMUg4Bf SEBDnnfl26th0hi+DinbnglZqXXmQUbZInjX02Svj3CA7eOFAnSg9kJxXKrHsx2NE2p/BGfp20Hyd33QSjL/eo5kQoevj5cdJ7tB65N8IOGcqO9/f4FpnWM4Dtl3mNgmkU1uWA9v8UnFv2hghs/DX9rzwFfGwcwhjpgUi6ZCFlXWIfzM0/q/n+E5AvkLYCYUYARcw3tObnUH8DFlHq5n80O/tVkPbJa23bPsK04oZDUjgLunnb2l7KQT0dQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: dax_iomap_pmd_fault() splits a huge PMD when the PMD fault falls back to PTE-level handling. The split is necessary so that the subsequent PTE fault does not misinterpret the huge PMD entry as a page table pointer. In practice this cannot fail today: DAX VMAs are always file-backed, and __split_huge_pmd() only allocates a PTE page table (the operation that can return -ENOMEM) for anonymous VMAs. For file-backed VMAs the split path simply zaps the PMD and returns 0. Use WARN_ON_ONCE to document this invariant and check the return value for __must_check compliance introduced in the next patch. Signed-off-by: Usama Arif --- fs/dax.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/fs/dax.c b/fs/dax.c index a5237169b4679..ed1859e8a916f 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -2039,7 +2039,14 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, unsigned long *pfnp, dax_unlock_entry(&xas, entry); fallback: if (ret == VM_FAULT_FALLBACK) { - split_huge_pmd(vmf->vma, vmf->pmd, vmf->address); + /* + * split_huge_pmd() cannot fail for file-backed (DAX) VMAs + * since splitting only zaps the PMD without allocating a + * PTE page table. + */ + if (WARN_ON_ONCE(split_huge_pmd(vmf->vma, vmf->pmd, + vmf->address))) + ret = VM_FAULT_OOM; count_vm_event(THP_FAULT_FALLBACK); } out: -- 2.52.0