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=1793221029; b=SvnbMzkIPVJtTcqKadTpfx9NafqYC5lYBAT6PneTIPpCAeG78fLiW+KNTCRntzmiPLav E3jUwYmwD2yE4Z5LKo+PFvbgtnayUGNxEiaktFI0Bw6QbGHVSOoY2CUUMfjWzscNCXdwI t+JGSNwD6ejnP8+Ue4lC8WACqj2Y6v40Zr0RuIp6hTGiKwbYmXqr1ek9J8CsQgtyYgj9n +uG0n6nFk8t2lC+EpyXI6+laRNYhNksk/qUeDxu4zJwdGn8HrtMFNqf2o1St3yc8x2MyC A5gkr1U+/XIV0FWWgU9C+4cnEhAf7IGZZ8w6pGHcVHzhqRgluQ76lEGYFkh3vYO0e+w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793221029; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=VBRXJGFXK0qCkmji9XuilGdSC6PWUqjPX0mT1B8+Dew=; b=CQPqI6AT/BuiRazp1myyc9Ae1zAuRlqSazuzLPp/5M2e3/x6iywOHPUPTYlDViahmDi1 YGDFzwb/Efwx7sbJfTqyidmyIO4Fc970ZcHmeRPG04MtIMKsH1wrwprxTdfAJ5ovXqYzR i7qS4KFJUpl3XHhL6g+2zOqquWMbcL+J50TOlxpdF/vz/td/5oZrDQHy77XMIF13vXN4S ZLUVI+DLvLFMeTYSfvzddH4enMwZZMweZmVPpRoLkKNYWRyxjuRngnRYfjWejHzhJEUhU /5SSpYSZxFVi3UedOR2L6gK/L3rhs4I2wv/k1E8ZAiZ/uPquIIYiycTmK5Q6bUN57vg== 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=d6++6R92; 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 44309606A322; Wed, 28 Oct 2026 20:57:09 +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=d6++6R92 Received: by smtp.kernel.org (Postfix) with ESMTPSA id C08141F01825; Wed, 28 Oct 2026 20:56:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793221028; bh=VBRXJGFXK0qCkmji9XuilGdSC6PWUqjPX0mT1B8+Dew=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=d6++6R92Y9pW/L7qdwwXGd0u/fINnIlp1NYiXwaft8WuvM2tnh59aB+MIfDwM3CYs 7OBmLdZ2yf/hpA8zpc7z5GdDAf3CTGmZVsA0hpoyhtF6kc1L6FM9QY6FPQzJGgCNiM 9Gle+WZku0sAgiTcOS5G2JnLcI+qrDvkcNMlVF6RCTWmoNWW7uHd+G1PGIIff8zlHa fPM56Qjn7U5XHgFTGxseW76jmouqIFti8WxpybzmVtUdGoYf7HNRmalUpxMtAY3Qao mgALZ2krEDvrdX6MlU+nCOicB8+IQASXlEKAHYsbgLpoWmWmdQnVWuDP0TEVs7UF1Z xjngcVGllnCNA== Message-ID: Date: Wed, 28 Oct 2026 21:56:42 +0100 X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 08/46] mm/filemap: finish fault cleanup before dropping the fault lock To: Thadeu Lima de Souza Cascardo Cc: 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 , 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, stable@vger.kernel.org, Chris Mason References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> <20261027-fixes_core-v1-8-6f74bec9a5bb@kernel.org> From: "David Hildenbrand (Arm)" 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/28/26 20:26, Thadeu Lima de Souza Cascardo wrote: > On Tue, Oct 27, 2026 at 12:17:28AM +0100, David Hildenbrand (Arm) wrote: >> On a retried fault, a fatal signal interrupting the folio lock wait >> makes lock_folio_maybe_drop_mmap() drop the fault lock without pinning >> the file. However, filemap_fault() may still need to release >> mapping->invalidate_lock. A concurrent munmap() can release the last >> file reference and free the mapping before that unlock. >> >> Defer dropping the fault lock to filemap_fault()'s retry cleanup, after >> releasing invalidate_lock. If the fault lock was already dropped for >> I/O, release the existing file reference instead. Keep the fault lock >> held for FAULT_FLAG_RETRY_NOWAIT as before. >> >> Fixes: 730633f0b7f9 ("mm: Protect operations adding pages to page cache with invalidate_lock") >> Cc: stable@vger.kernel.org >> Reported-by: Chris Mason >> Signed-off-by: David Hildenbrand (Arm) >> --- >> mm/filemap.c | 37 +++++++++++++------------------------ >> 1 file changed, 13 insertions(+), 24 deletions(-) >> >> diff --git a/mm/filemap.c b/mm/filemap.c >> index 6b5e1d866a9e0..b04be64a5069f 100644 >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -3308,11 +3308,11 @@ loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start, >> * @folio - the folio to lock. >> * @fpin - the pointer to the file we may pin (or is already pinned). >> * >> - * This works similar to lock_folio_or_retry in that it can drop the >> - * mmap_lock. It differs in that it actually returns the folio locked >> - * if it returns 1 and 0 if it couldn't lock the folio. If we did have >> - * to drop the mmap_lock then fpin will point to the pinned file and >> - * needs to be fput()'ed at a later point. >> + * Returns 1 with the folio locked, or 0 if locking failed. >> + * >> + * On both entry and return, a non-NULL *fpin means the fault lock has >> + * already been dropped and the caller must eventually fput() the file. >> + * Otherwise the fault lock is still held, including on failure. >> */ >> static int lock_folio_maybe_drop_mmap(struct vm_fault *vmf, struct folio *folio, >> struct file **fpin) >> @@ -3329,21 +3329,9 @@ static int lock_folio_maybe_drop_mmap(struct vm_fault *vmf, struct folio *folio, >> return 0; >> >> *fpin = maybe_unlock_mmap_for_io(vmf, *fpin); >> - if (vmf->flags & FAULT_FLAG_KILLABLE) { >> - if (__folio_lock_killable(folio)) { >> - /* >> - * We didn't have the right flags to drop the >> - * fault lock, but all fault_handlers only check >> - * for fatal signals if we return VM_FAULT_RETRY, >> - * so we need to drop the fault lock here and >> - * return 0 if we don't have a fpin. >> - */ >> - if (*fpin == NULL) >> - release_fault_lock(vmf); >> - return 0; >> - } >> - } else >> - __folio_lock(folio); >> + if (vmf->flags & FAULT_FLAG_KILLABLE) >> + return !__folio_lock_killable(folio); >> + __folio_lock(folio); >> >> return 1; >> } >> @@ -3572,7 +3560,7 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf) >> * vma->vm_mm->mmap_lock must be held on entry. >> * >> * If our return value has VM_FAULT_RETRY set, it's because the mmap_lock >> - * may be dropped before doing I/O or by lock_folio_maybe_drop_mmap(). >> + * may be dropped before doing I/O or when aborting an interrupted wait. >> * >> * If our return value does not have VM_FAULT_RETRY set, the mmap_lock >> * has not been released. >> @@ -3728,9 +3716,8 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) >> >> out_retry: >> /* >> - * We dropped the mmap_lock, we need to return to the fault handler to >> - * re-find the vma and come back and find our hopefully still populated >> - * page. >> + * With fpin set, the fault lock was already dropped. Otherwise it is >> + * still held. Release invalidate_lock before dropping either protection. >> */ >> if (!IS_ERR(folio)) >> folio_put(folio); >> @@ -3738,6 +3725,8 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) >> filemap_invalidate_unlock_shared(mapping); >> if (fpin) >> fput(fpin); >> + else if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) >> + release_fault_lock(vmf); >> return ret | VM_FAULT_RETRY; >> } >> EXPORT_SYMBOL(filemap_fault); >> >> -- >> 2.43.0 >> >> > > If I understood this correctly, the invariant is that if fpin is set, then > the fault lock has been dropped. > > At first, I was confused that maybe_unlock_mmap_for_io drops the fault > lock, but in that case, it also gets a reference to the file, so fpin is > set and the invariant is kept. lock_folio_maybe_drop_mmap() and the other functions here are horrible, horrible stuff, really :( Thanks! -- Cheers, David