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 4540EC43458 for ; Wed, 1 Jul 2026 14:07:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1BC8C6B00AF; Wed, 1 Jul 2026 10:07:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 16D026B00BA; Wed, 1 Jul 2026 10:07:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 035B96B00BB; Wed, 1 Jul 2026 10:07:22 -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 C86AF6B00AF for ; Wed, 1 Jul 2026 10:07:22 -0400 (EDT) Received: from smtpin24.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 527431669A3 for ; Wed, 1 Jul 2026 14:07:22 +0000 (UTC) X-FDA: 84940385124.24.9ADC39B Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) by imf26.hostedemail.com (Postfix) with ESMTP id DB59E14000C for ; Wed, 1 Jul 2026 14:07:18 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=VSR20mxP; spf=pass (imf26.hostedemail.com: domain of usama.arif@linux.dev designates 95.215.58.178 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1782914840; b=d7wmhnfBzODd6bB3VYt3jvdscTJ5p4PeDahrQMMlo+XvBCOE46p8/Fdawtw/eTTu8RGxr8 ZvByUIQV3V5GKHaFvwlJZUd3fPxVjGC7h399zcue8SJA3uJycreHXyQJEzdu9skNv1DqcN B1gCWCwLQO+HzqgYWAUJPDKEptULebg= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782914840; 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:references:dkim-signature; bh=+oTWLw7UwF38UExEYP9OuHXWaad05pihfyj+4u0Flgs=; b=xK0X0+vmgbI9ZWPUmwnR02bZg1CskxVBxX3fPNdZm09o/HomcEi1vFXHXHKY2UtRKfeF/2 auSc7BmGijUTDbyUZKBMYjwh3yBlfUrI44PHPeMMQGOlrOuap2+8zGcRsXfeOnGOIA3Gs6 vcBA36029+LxM4unAu4qOq2agC3HqR8= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=VSR20mxP; spf=pass (imf26.hostedemail.com: domain of usama.arif@linux.dev designates 95.215.58.178 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=1782914835; 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; bh=+oTWLw7UwF38UExEYP9OuHXWaad05pihfyj+4u0Flgs=; b=VSR20mxPyhfE0mj0ljIXKzkdvtBwXGGCPBjDGG+X1r+9yhEDmiO2Fwnpg2YmCdZjA3qFiU ARmhEWvOwGwgRez4vWCQFGNS4X3L4b2g1ymqpkvattNgyMjIcu5sWHw37VAB/vSPP8BF9r OIb7mGsX+u6jnJ1swL63SSYXMKCw4/Y= From: Usama Arif To: Andrew Morton , apopple@nvidia.com, byungchul@sk.com, david@kernel.org, gourry@gourry.net, joshua.hahnjy@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, matthew.brost@intel.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, ziy@nvidia.com Cc: shakeel.butt@linux.dev, hannes@cmpxchg.org, kernel-team@meta.com, Usama Arif , sashiko-bot Subject: [PATCH] mm/migrate_device: pin large folios before splitting Date: Wed, 1 Jul 2026 07:06:38 -0700 Message-ID: <20260701140638.840773-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: hhzzsbms4yjx4tyx3ywx687cz54eenbe X-Rspamd-Queue-Id: DB59E14000C X-Rspamd-Server: rspam06 X-HE-Tag: 1782914838-236551 X-HE-Meta: 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 6q76RqHZ DMDPEkf0+c2e5yEssM9syBDvsRZPqVEVIccI/cSbKicOazLXWRkI9x7p0S7IOl5FSKtTGCua3U2fjXVW73u2yMQ+hGYQJd9HLyEENBT67JUaVvuBvk5XNK7rQF7RF73SdM4ejEQOLt/WQ6wR6WEPYZMv6vnTXjla++QRSESsbSDIuI6pgc1MYf7B9QGYFbRRe1ddRY9lWE08cCpAUm8ulVI36GpDchcNiW5+ELFwnE3nwlOAi7q+LkPmrxZxXMwcPod9d6W+toWVQCfmwxAC/p8NVH4Pr/VU41IZRFtxcmJpCzmg3z1sFNWHYgiABEFWXJK+3rEtTdAgV3ZvL8WZu2iF9lixj3wV28y58kcedIe/qolvRBNAxJs5AgzyLQ7wHblovAf7IxejeWoYJVyY5dbjlAQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: migrate_vma_collect_pmd() can detect a large folio while holding the PTE lock, then drop the PTE lock before calling migrate_vma_split_folio(). The split helper took its own reference, but only after the lock had already been dropped. One way to hit this is device migration over a range that contains a large folio. The walker reads the PTE while holding the PTE lock and derives the folio either from a present PTE via vm_normal_page(), or from a non-present PTE that encodes a device-private softleaf entry. It then has to drop the PTE lock because split_folio() can block. Before migrate_vma_split_folio() gets a folio reference, concurrent reclaim, migration, or truncation can replace or clear the entry and drop the last reference to the folio. The split helper would then take a reference and lock on a stale folio pointer. Take a temporary reference before dropping the PTE lock and pass that reference into migrate_vma_split_folio(). The helper consumes the reference, so split_folio() still sees only the expected caller pin instead of an extra pin that could make the split fail. Reported-by: sashiko-bot Link: https://sashiko.dev/#/patchset/20260630164143.1595669-1-usama.arif%40linux.dev Fixes: 022a12deda53 ("mm/migrate_device: handle partially mapped folios during collection") Signed-off-by: Usama Arif --- mm/migrate_device.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 2f8b646302c2..f5a5f699e98e 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -77,6 +77,9 @@ static int migrate_vma_collect_hole(unsigned long start, * @folio: the folio to split * @fault_page: struct page associated with the fault if any * + * If @folio is not the folio containing @fault_page, the caller must hold a + * reference on @folio. The helper consumes that reference. + * * Returns 0 on success */ static int migrate_vma_split_folio(struct folio *folio, @@ -86,10 +89,8 @@ static int migrate_vma_split_folio(struct folio *folio, struct folio *fault_folio = fault_page ? page_folio(fault_page) : NULL; struct folio *new_fault_folio = NULL; - if (folio != fault_folio) { - folio_get(folio); + if (folio != fault_folio) folio_lock(folio); - } ret = split_folio(folio); if (ret) { @@ -310,6 +311,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, if (folio_test_large(folio)) { int ret; + /* + * Keep the folio stable after dropping the PTE + * lock. migrate_vma_split_folio() consumes this + * reference. + */ + if (folio != fault_folio) + folio_get(folio); lazy_mmu_mode_disable(); pte_unmap_unlock(ptep, ptl); ret = migrate_vma_split_folio(folio, @@ -353,6 +361,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, if (folio && folio_test_large(folio)) { int ret; + /* + * Keep the folio stable after dropping the + * PTE lock. migrate_vma_split_folio() consumes + * this reference. + */ + if (folio != fault_folio) + folio_get(folio); lazy_mmu_mode_disable(); pte_unmap_unlock(ptep, ptl); ret = migrate_vma_split_folio(folio, -- 2.53.0-Meta