From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793439802; b=UiWCDSBMoIMEoGjyNdM/JUKhIEFw9KQSMyO0LA4dzef51bVCmCFfNYoPjlour30Bg8pM 1HPqwAITsxhhjTnkFEsqWYRYeboHuigNOnq53BXeuSjPOZ8MhxnU7dzGlUg23CViP1TYY eCoLsKsDPUKcc+8xyRILO4b2H1r1QJXCiovtLy/MFkZZIemLzcCI0H4ieF84NOd0gjGSx E9TrFc0Fv+G97c12OF/h946PAR3DEAlYWNHIBDNj3sZvud10dwQVCYLKEGLHCt66amvCd eWXx2aGXqhF6Lm8OSTQ7SAwllG4wRyD/qVCKleR3Au9zUApjqwuWBkPL8xKuiSnqwqA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793439802; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=GgO1WtfTPr95CMg999FmZUV6ZtgV/+NdH4f6NGhd5j0=; b=RvfbIYxi1j3Wu/S71VItxjsZDlkrUpXf0Kgc7OvT8aehGgKFGk8VDQLn3b1ThRl3xb4Y 0PKVu7ag+sRMyxWZbA4fWKGRw3/9dnKRAAiwOGsK6vmmUUyH/7DpfjOD69gTzgAmeGsR3 LTt31+Xsd7icAzLZjUlEDprSlS5ORAHKY6LVsssOzx89KoHEjHaMUaxxCeasFnJhXCcrj A/9QkFkDWddRXi/YOl2wULfHJP1sUGNOCWSMph3NM2PI9WCMMrwQ7TnKak5auLwQv/8S+ K0Ql2IE2pkQs3Op4miN9RT1dEmW1Ojx6zWPfFNSRdjZkN57F0cg7FRNY3np2aTrL9gw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=CxsFcgDy; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6374E606A31A; Sat, 31 Oct 2026 09:43:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=CxsFcgDy Received: by smtp.kernel.org (Postfix) with ESMTPSA id 160C51F00919; Sat, 31 Oct 2026 09:43:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793439802; bh=GgO1WtfTPr95CMg999FmZUV6ZtgV/+NdH4f6NGhd5j0=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=CxsFcgDyR62puXwpfrdBVjYlxXqi56LRd0wVMMbXZa5WFwuvsy+6B5cy3b5Iwa7MG 8sBreHtjQSLv2LeLQKpzyJ9OA/zafCF1rZfSEe71N8/KoTuH72Iv5RrwCIu6BR776N rit21O2a2/iegjkgJJmtCXLN/B5tjBc0jHK5yfrE3y3//41Tqx3IWR5oe4TS+os+n6 ptEh7dACU7b2BPKFq38dpUCDEsrJ22Xstg+i7L5YBJ9fCPw4qlIKnuDlvaG8jeKsdk BkK2l2ir4IGtFTyrtwd8Hn8khr+C9Zv5YUX+w0Yu3RfTm9WrN67lUNWU9CeYw8a5vf ObyYSDr/u9RcA== From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:39:41 +0100 Subject: [PATCH v3 12/47] mm/huge_memory: fix livelock on device private folio X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261031-fixes_core-v3-12-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> In-Reply-To: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> To: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Josef Bacik , Muhammad Usama Anjum , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2310; i=david@kernel.org; h=from:subject:message-id; bh=rOFEKHXFU3ik6VWKIWSfoeHTdwlufJwdJhailtQlKpY=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLKebk/za/NTTZLZMb9d0VIwTeN1JKe3lyNXr2ZuQ2vQL Sd5S7uOUhYGMQ4GWTFFlqDg+wYvX66rrXbjY4aZw8oEMoSBi1MAJjK1geF/tMmjs8UW6zzCmsKP 8PM9FLOuXFwt+GBBhUqxj81F95jVjAxT18xRsTObx+3OeGvHkv7eWddSHXf02q6afunNbalWsQ+ 8AA== X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A From: Josef Bacik If do_huge_pmd_device_private() cannot lock the folio, it simply returns to try again on the next fault. Just like we did in commit b570f37a2ce4 ("mm: Fix a hmm_range_fault() livelock / starvation problem"), let's wait for the softleaf entry, which will drop the PTL and wait until the folio was unlocked. This is precisely what we do in do_swap_page() with device-private folios. This avoids possibly livelocking. Update softleaf_entry_wait_on_locked() documentation to clarify that device-private entries wait until the folio is unlocked. There seems to be no compelling reason to backport this to stable kernels unless we actually see problems there. Fix generated by an LLM and sent by Josef Bacik in private. Fixes: 4964099163d0 ("mm/memory/fault: add THP fault handling for zone device private pages") Signed-off-by: Josef Bacik [ david: simplify patch description, fixup softleaf_entry_wait_on_locked description] Reviewed-by: Zi Yan Reviewed-by: Lance Yang Tested-by: Muhammad Usama Anjum Signed-off-by: David Hildenbrand (Arm) --- mm/filemap.c | 4 ++-- mm/huge_memory.c | 2 +- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index b04be64a5069f..e85a4114d2ecc 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1395,8 +1395,8 @@ static inline int folio_wait_bit_common(struct folio *folio, int bit_nr, #ifdef CONFIG_MIGRATION /** - * softleaf_entry_wait_on_locked - Wait for a migration entry or - * device_private entry to be removed. + * softleaf_entry_wait_on_locked - Wait for a migration entry to be removed + * or a device-private folio in a device-private entry to get unlocked. * @entry: migration or device_private swap entry. * @ptl: already locked ptl. This function will drop the lock. * diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 283c4bc8b927c..2b31a425c7a32 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1500,7 +1500,7 @@ vm_fault_t do_huge_pmd_device_private(struct vm_fault *vmf) folio_unlock(folio); folio_put(folio); } else { - spin_unlock(ptl); + softleaf_entry_wait_on_locked(entry, ptl); } return ret; -- 2.43.0