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 4AFE035A95A for ; Fri, 9 Jan 2026 13:50:33 +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=1767966633; cv=none; b=NeNL1nLr0+9oySdkacRsRkIlbpeAdTgoJwbLxZ10foOYpajVkCbSLDXNgguegpUzWcLUl7JSh5b1sV57SJwMTmfe1qehvHx7J2mv1ERFGWOc1gK0tJPw9ODchKkqyTN5yslpjD8OBsWQKaRSJ7VWx3uI6Ix3yCFHK7PA9kvWkTY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767966633; c=relaxed/simple; bh=QRvCDtIt9FY0lIy6CkBLbcgCIbaVCMHdCdDA4vRtluk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=NjvX+KQcPpZVRNdnKlDDuAnN2SHKrehhDgn2Eb8Onr2+FzZ2XDCYcVTUpJsY6zUo7tDl/xxpmsRz0impvGpOTzxvKl66BbJAOgzgL+2Gduss0eDVSWUY5rQ528MrtY6CiAQ74E/1lLLY73LqZDI31yafBcuRjsfPFG90TlsZTwI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PhXFGafi; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PhXFGafi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 491ACC19423; Fri, 9 Jan 2026 13:50:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767966632; bh=QRvCDtIt9FY0lIy6CkBLbcgCIbaVCMHdCdDA4vRtluk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PhXFGafiwpuu6FCohCNJs5NTLwUgruXRPWdi1r+BOSag3o/2zjDcjir3tAqeIOQfY ZPlZc/WFppmbdrSYB7x0FNnZl8btpy9SdOrSllVm5VmOxrJDgKyvibOMiSEHbu4Uoa FKKL1bFxd5wXQJ1E89u9pI1umuSK1FtQEBIoAAfdfUCFydc02HaSLL2571Y8fmh/s4 EX/XAR1F8TmMj87g5aCelA2TV0DQsVXTTpq0Sh8L4Wbci3EY70def56ZIZnqY+PVcI vWFA3JXOIVvuep+7DHQYxpbBSgTTQ/2nPN2sHgdEZBKvaMb0txbyyGxYYVjfQLZ9v2 DfmbdTDG3o2jQ== Message-ID: <509ac447-e5a7-4cba-86b8-e9c0e72fc93c@kernel.org> Date: Fri, 9 Jan 2026 14:50:26 +0100 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] migrate: Correct lock ordering for hugetlb file folios To: "Matthew Wilcox (Oracle)" , Andrew Morton Cc: Zi Yan , Lorenzo Stoakes , Rik van Riel , "Liam R. Howlett" , Vlastimil Babka , Harry Yoo , Jann Horn , linux-mm@kvack.org, syzbot+2d9c96466c978346b55f@syzkaller.appspotmail.com, Lance Yang , stable@vger.kernel.org References: <20260109041345.3863089-1-willy@infradead.org> <20260109041345.3863089-2-willy@infradead.org> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAa2VybmVsLm9yZz7CwY0EEwEIADcWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaKYhwAIbAwUJJlgIpAILCQQVCgkIAhYCAh4FAheAAAoJEE3eEPcA/4Naa5EP/3a1 9sgS9m7oiR0uenlj+C6kkIKlpWKRfGH/WvtFaHr/y06TKnWn6cMOZzJQ+8S39GOteyCCGADh 6ceBx1KPf6/AvMktnGETDTqZ0N9roR4/aEPSMt8kHu/GKR3gtPwzfosX2NgqXNmA7ErU4puf zica1DAmTvx44LOYjvBV24JQG99bZ5Bm2gTDjGXV15/X159CpS6Tc2e3KvYfnfRvezD+alhF XIym8OvvGMeo97BCHpX88pHVIfBg2g2JogR6f0PAJtHGYz6M/9YMxyUShJfo0Df1SOMAbU1Q Op0Ij4PlFCC64rovjH38ly0xfRZH37DZs6kP0jOj4QdExdaXcTILKJFIB3wWXWsqLbtJVgjR YhOrPokd6mDA3gAque7481KkpKM4JraOEELg8pF6eRb3KcAwPRekvf/nYVIbOVyT9lXD5mJn IZUY0LwZsFN0YhGhQJ8xronZy0A59faGBMuVnVb3oy2S0fO1y/r53IeUDTF1wCYF+fM5zo14 5L8mE1GsDJ7FNLj5eSDu/qdZIKqzfY0/l0SAUAAt5yYYejKuii4kfTyLDF/j4LyYZD1QzxLC MjQl36IEcmDTMznLf0/JvCHlxTYZsF0OjWWj1ATRMk41/Q+PX07XQlRCRcE13a8neEz3F6we 08oWh2DnC4AXKbP+kuD9ZP6+5+x1H1zEzsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCgh Cj/CA/lc/LMthqQ773gauB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseB fDXHA6m4B3mUTWo13nid0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts 6TZ+IrPOwT1hfB4WNC+X2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiu Qmt3yqrmN63V9wzaPhC+xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKB Tccu2AXJXWAE1Xjh6GOC8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvF FFyAS0Nk1q/7EChPcbRbhJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh 2YmnmLRTro6eZ/qYwWkCu8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRk F3TwgucpyPtcpmQtTkWSgDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0L LH63+BrrHasfJzxKXzqgrW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4v q7oFCPsOgwARAQABwsF8BBgBCAAmAhsMFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmic2qsF CSZYCKEACgkQTd4Q9wD/g1oq0xAAsAnw/OmsERdtdwRfAMpC74/++2wh9RvVQ0x8xXvoGJwZ rk0Jmck1ABIM//5sWDo7eDHk1uEcc95pbP9XGU6ZgeiQeh06+0vRYILwDk8Q/y06TrTb1n4n 7FRwyskKU1UWnNW86lvWUJuGPABXjrkfL41RJttSJHF3M1C0u2BnM5VnDuPFQKzhRRktBMK4 GkWBvXlsHFhn8Ev0xvPE/G99RAg9ufNAxyq2lSzbUIwrY918KHlziBKwNyLoPn9kgHD3hRBa Yakz87WKUZd17ZnPMZiXriCWZxwPx7zs6cSAqcfcVucmdPiIlyG1K/HIk2LX63T6oO2Libzz 7/0i4+oIpvpK2X6zZ2cu0k2uNcEYm2xAb+xGmqwnPnHX/ac8lJEyzH3lh+pt2slI4VcPNnz+ vzYeBAS1S+VJc1pcJr3l7PRSQ4bv5sObZvezRdqEFB4tUIfSbDdEBCCvvEMBgoisDB8ceYxO cFAM8nBWrEmNU2vvIGJzjJ/NVYYIY0TgOc5bS9wh6jKHL2+chrfDW5neLJjY2x3snF8q7U9G EIbBfNHDlOV8SyhEjtX0DyKxQKioTYPOHcW9gdV5fhSz5tEv+ipqt4kIgWqBgzK8ePtDTqRM qZq457g1/SXSoSQi4jN+gsneqvlTJdzaEu1bJP0iv6ViVf15+qHuY5iojCz8fa0= In-Reply-To: <20260109041345.3863089-2-willy@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/9/26 05:13, Matthew Wilcox (Oracle) wrote: > Syzbot has found a deadlock (analyzed by Lance Yang): > > 1) Task (5749): Holds folio_lock, then tries to acquire i_mmap_rwsem(read lock). > 2) Task (5754): Holds i_mmap_rwsem(write lock), then tries to acquire > folio_lock. > > migrate_pages() > -> migrate_hugetlbs() > -> unmap_and_move_huge_page() <- Takes folio_lock! > -> remove_migration_ptes() > -> __rmap_walk_file() > -> i_mmap_lock_read() <- Waits for i_mmap_rwsem(read lock)! > > hugetlbfs_fallocate() > -> hugetlbfs_punch_hole() <- Takes i_mmap_rwsem(write lock)! > -> hugetlbfs_zero_partial_page() > -> filemap_lock_hugetlb_folio() > -> filemap_lock_folio() > -> __filemap_get_folio <- Waits for folio_lock! As raised in the other patch I stumbled over first: We now handle file-backed folios correctly I think. Could we somehow also be in trouble for anon folios? Because there, we'd still take the rmap lock after grabbing the folio lock. > > The migration path is the one taking locks in the wrong order according > to the documentation at the top of mm/rmap.c. So expand the scope of the > existing i_mmap_lock to cover the calls to remove_migration_ptes() too. > > This is (mostly) how it used to be after commit c0d0381ade79. That was > removed by 336bf30eb765 for both file & anon hugetlb pages when it should > only have been removed for anon hugetlb pages. > > Fixes: 336bf30eb765 (hugetlbfs: fix anon huge page migration race) > Reported-by: syzbot+2d9c96466c978346b55f@syzkaller.appspotmail.com > Link: https://lore.kernel.org/all/68e9715a.050a0220.1186a4.000d.GAE@google.com > Debugged-by: Lance Yang > Signed-off-by: Matthew Wilcox (Oracle) > Cc: stable@vger.kernel.org > --- > mm/migrate.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 5169f9717f60..4688b9e38cd2 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1458,6 +1458,7 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio, > int page_was_mapped = 0; > struct anon_vma *anon_vma = NULL; > struct address_space *mapping = NULL; > + enum ttu_flags ttu = 0; > > if (folio_ref_count(src) == 1) { > /* page was freed from under us. So we are done. */ > @@ -1498,8 +1499,6 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio, > goto put_anon; > > if (folio_mapped(src)) { > - enum ttu_flags ttu = 0; > - > if (!folio_test_anon(src)) { > /* > * In shared mappings, try_to_unmap could potentially > @@ -1516,16 +1515,17 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio, > > try_to_migrate(src, ttu); > page_was_mapped = 1; > - > - if (ttu & TTU_RMAP_LOCKED) > - i_mmap_unlock_write(mapping); > } > > if (!folio_mapped(src)) > rc = move_to_new_folio(dst, src, mode); > > if (page_was_mapped) > - remove_migration_ptes(src, !rc ? dst : src, 0); > + remove_migration_ptes(src, !rc ? dst : src, > + ttu ? RMP_LOCKED : 0); (ttu & TTU_RMAP_LOCKED) ? RMP_LOCKED : 0) Would be cleaner, but I see how you clean that up in #2. :) Acked-by: David Hildenbrand (Red Hat) -- Cheers David