From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 45B56606A31E for ; Wed, 28 Oct 2026 20:57:13 +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 kanga.kvack.org (Postfix) id 5A4D66B05B2; Wed, 28 Oct 2026 16:57:12 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5557F6B05B3; Wed, 28 Oct 2026 16:57:12 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3F7126B05B4; Wed, 28 Oct 2026 16:57:12 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 116126B05B2 for ; Wed, 28 Oct 2026 16:57:11 -0400 (EDT) Received: from smtpin20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 87000801E3 for ; Wed, 28 Oct 2026 20:57:11 +0000 (UTC) X-FDA: 85373245062.20.A711987 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf12.hostedemail.com (Postfix) with ESMTP id AE3544000A for ; Wed, 28 Oct 2026 20:57:09 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=d6++6R92; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf12.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793221029; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=VBRXJGFXK0qCkmji9XuilGdSC6PWUqjPX0mT1B8+Dew=; b=upBZkJ6J1iyH1W9aXO799GoZj1WCp+cxEMh8wt44jmFrBi7CSQZMJYqrKrX/a26fdZwU0G 3alfW+KbYmvPVw445sGzcOiEf2xz8syKIMg3tYXwDfh6cCEv/VM1gRwSje+qeIDKzSRdTl 3670rqyGuMrbKaZuwgwEU16F04MIXyE= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=d6++6R92; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf12.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793221029; b=2yJrW80kYvxn7MEos/bw/0ukojwIiOjQuBNKBuIUSdOmb+0fxJjRNZ3UxAQBe0k+drqDSM cHyu5gXwL6bCfCAwOjiRjeYzYWUu5yTeW33ydHz+RvS0uC6Cnk+kXpUZyC3H3Yo5uoYfW2 auEwwgtoYuF36HN8TmLVGmJtLvsTExk= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 06E3040435; Wed, 28 Oct 2026 20:57:09 +0000 (UTC) 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-Archived-By: 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; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: AE3544000A X-Stat-Signature: rcini1onm66rfu6xa14syj4tqworbh3c X-Spam-Status: No, score=-17.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793221029-523701 X-HE-Meta: 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 voXfOhPw 5eLzY3Yvvcns85ouuNk17/lbnganqrJhmw1wGSlnbVJ7982daAOBHeLFoErDHqyofj8ajF0Szr4vkXH1/r9ivpBUsAqM+PGa9cxqNqrUL4O7PHYzDI5eNVxwdaMwhBkYf2o20wudxLh1RTHev8f6MBY+eEe5cHoEPS09TulRhppZQfdqtS8nyTYKhU6SCowlBDupRoIJeSG5ArDbKOZbF/o/n5Ul+vHE9vjBqc/Yx5FhKjWEeq5ESYhDB65wYB37/Lqjn9+4ZA/vv7DazPQ6Xvu4UdSlVKnqMCKztFIf9u4RPjyhv5FzvGkz7fGKuXYgpj7BrfBDTi3vnXrMUflFKaaCjLa6+HCf0Uv7HwN289hn9Z+o= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 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