From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4C488364EBA; Wed, 1 Apr 2026 23:20:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775085600; cv=none; b=FV79Rv8LhhXhFcFyJye7oMIglSO7dmNvvKranxHdpXNU0BANktEAo/2hS6m8Ra82bz6ovYP/OJQHSAXIBC2lKGG+lAcOLte3Yzwhyh31Ux2C4wcKrvswvLZsOwfOUjjN7PiOItxXNZYUX3P7vgIlwLbxKdV7fslohlzGLd+KvX0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775085600; c=relaxed/simple; bh=tE1I6QqGm0tUZMScDuiyoHJK4m2GtY03FdDFEhbLMBY=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=G7ymlKqh0PxbxrCD6Bbc8JGDbpH7ol0tQE3Kl7AI46z63cSEY3WqoCHxDikNY1UtV5ZGj2CMehM6n2DX+VYue8bFAHwKpQ9PZCQtFfzXdFWrZ0rvlV2TCfDDBS6l4Xn/OKTwbPyNhkm6up6kZ+S1q3YMw4FPOUr7qIY6Unmo5+s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=TMkszWqQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="TMkszWqQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 26513C4CEF7; Wed, 1 Apr 2026 23:19:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1775085599; bh=tE1I6QqGm0tUZMScDuiyoHJK4m2GtY03FdDFEhbLMBY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=TMkszWqQ7EaxmW4yhB5tGTUs1Tu1rc9aZVXZf/+1lHc2CQMdR/Sj2aa5QxfsWKMek q8cphQkovBOxKE2l+OpHWdUv4ypVBEJazmcOs28A8oWpZiCKQZuo+CP9I48bHJr5// FuuUX/5PKBn69LPTQbyXt1dHX7yLJXElk7f72hws= Date: Wed, 1 Apr 2026 16:19:58 -0700 From: Andrew Morton To: Zi Yan Cc: Lance Yang , david@kernel.org, ljs@kernel.org, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, richard.weiyang@gmail.com, usama.arif@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kartikey406@gmail.com, syzbot+a7067a757858ac8eb085@syzkaller.appspotmail.com, stable@vger.kernel.org Subject: Re: [PATCH mm-unstable 1/1] mm: fix deferred split queue races during migration Message-Id: <20260401161958.38ab50f44e7629e6475d3eca@linux-foundation.org> In-Reply-To: References: <20260401131032.13011-1-lance.yang@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 01 Apr 2026 18:55:48 -0400 Zi Yan wrote: > Can you apply the fixup below to move the comment? Lance told me he > would be away for a while, so he could not send a fixup to move > the comment. Thanks. I folded that into Lance's base patch so here's the whole thing: From: Lance Yang Subject: mm: fix deferred split queue races during migration Date: Wed, 1 Apr 2026 21:10:32 +0800 migrate_folio_move() records the deferred split queue state from src and replays it on dst. Replaying it after remove_migration_ptes(src, dst, 0) makes dst visible before it is requeued, so a concurrent rmap-removal path can mark dst partially mapped and trip the WARN in deferred_split_folio(). Move the requeue before remove_migration_ptes() so dst is back on the deferred split queue before it becomes visible again. Because migration still holds dst locked at that point, teach deferred_split_scan() to requeue a folio when folio_trylock() fails. Otherwise a fully mapped underused folio can be dequeued by the shrinker and silently lost from split_queue. [ziy@nvidia.com: move the comment] Link: https://lkml.kernel.org/r/FB71A764-0F10-4E5A-B4A0-BA4C7F138408@nvidia.com Link: https://syzkaller.appspot.com/bug?extid=a7067a757858ac8eb085 Link: https://lkml.kernel.org/r/20260401131032.13011-1-lance.yang@linux.dev Fixes: 8a8ca142a488 ("mm: migrate: requeue destination folio on deferred split queue") Signed-off-by: Lance Yang Signed-off-by: Zi Yan Reported-by: syzbot+a7067a757858ac8eb085@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-mm/69ccb65b.050a0220.183828.003a.GAE@google.com/ Suggested-by: David Hildenbrand (Arm) Acked-by: David Hildenbrand (Arm) Acked-by: Zi Yan Cc: Alistair Popple Cc: Baolin Wang Cc: Barry Song Cc: Byungchul Park Cc: David Hildenbrand Cc: Deepanshu Kartikey Cc: Dev Jain Cc: Gregory Price Cc: "Huang, Ying" Cc: Joshua Hahn Cc: Lance Yang Cc: Liam Howlett Cc: Lorenzo Stoakes (Oracle) Cc: Matthew Brost Cc: Nico Pache Cc: Rakie Kim Cc: Ryan Roberts Cc: Wei Yang Cc: Ying Huang Cc: Usama Arif Cc: Signed-off-by: Andrew Morton --- mm/huge_memory.c | 15 ++++++++++----- mm/migrate.c | 18 +++++++++--------- 2 files changed, 19 insertions(+), 14 deletions(-) --- a/mm/huge_memory.c~mm-fix-deferred-split-queue-races-during-migration +++ a/mm/huge_memory.c @@ -4542,7 +4542,7 @@ retry: goto next; } if (!folio_trylock(folio)) - goto next; + goto requeue; if (!split_folio(folio)) { did_split = true; if (underused) @@ -4551,13 +4551,18 @@ retry: } folio_unlock(folio); next: + /* + * If thp_underused() returns false, or if split_folio() + * succeeds, or if split_folio() fails in the case it was + * underused, then consider it used and don't add it back to + * split_queue. + */ if (did_split || !folio_test_partially_mapped(folio)) continue; +requeue: /* - * Only add back to the queue if folio is partially mapped. - * If thp_underused returns false, or if split_folio fails - * in the case it was underused, then consider it used and - * don't add it back to split_queue. + * Add back partially mapped folios, or underused folios that + * we could not lock this round. */ fqueue = folio_split_queue_lock_irqsave(folio, &flags); if (list_empty(&folio->_deferred_list)) { --- a/mm/migrate.c~mm-fix-deferred-split-queue-races-during-migration +++ a/mm/migrate.c @@ -1384,6 +1384,15 @@ static int migrate_folio_move(free_folio goto out; /* + * Requeue the destination folio on the deferred split queue if + * the source was on the queue. The source is unqueued in + * __folio_migrate_mapping(), so we recorded the state from + * before move_to_new_folio(). + */ + if (src_deferred_split) + deferred_split_folio(dst, src_partially_mapped); + + /* * When successful, push dst to LRU immediately: so that if it * turns out to be an mlocked page, remove_migration_ptes() will * automatically build up the correct dst->mlock_count for it. @@ -1399,15 +1408,6 @@ static int migrate_folio_move(free_folio if (old_page_state & PAGE_WAS_MAPPED) remove_migration_ptes(src, dst, 0); - /* - * Requeue the destination folio on the deferred split queue if - * the source was on the queue. The source is unqueued in - * __folio_migrate_mapping(), so we recorded the state from - * before move_to_new_folio(). - */ - if (src_deferred_split) - deferred_split_folio(dst, src_partially_mapped); - out_unlock_both: folio_unlock(dst); folio_set_owner_migrate_reason(dst, reason); _