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 7D7E6606A331 for ; Mon, 9 Nov 2026 09:50:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=OvHIGFuz Received: by kanga.kvack.org (Postfix) id 8C4F46B05BE; Mon, 9 Nov 2026 04:50:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8759C6B05BF; Mon, 9 Nov 2026 04:50:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7648D6B05C0; Mon, 9 Nov 2026 04:50:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 472296B05BE for ; Mon, 9 Nov 2026 04:50:33 -0500 (EST) Received: from smtpin17.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 9CB184062D for ; Mon, 9 Nov 2026 09:50:32 +0000 (UTC) X-FDA: 85415110704.17.5DFF813 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf07.hostedemail.com (Postfix) with ESMTP id D99B040006 for ; Mon, 9 Nov 2026 09:50:30 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=OvHIGFuz; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 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=1794217831; 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=8jQST5+SfU/stcEn1VOV+s+O2grX/AjdmKJu3mY8h/o=; b=s0Ezv9XbBTW/ijiLxGy+O1m1myUfrCwjA0T3OC3qCJIqzzffijlPzHK0yVBC6te3V8CLUL rQjbpbzELnmgNRMT8c1qh7MrgD3lYlHWo+TYXfUmMheoUuOla7rOCj4xGixlqKD/RqfllJ 8dID9HsiYAUmGtJnr9gXzXeGm+dMyhE= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=OvHIGFuz; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf07.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1794217831; b=hDjgcdSRct5uw7hULY6J+UCyzAczVNCwqKr1Hm/hk04r2iSJ9OywuVAhlyaQ81AcOsmTDo 8fIIhJwRFfPzIllkUD9MuEXc3khc5tFxRLeFg/0/5xXMvSvoCxqRA00q5lEIknyPFcpZnL jfKsANRKlG83oKPzyBy9T3zQhdsWBh0= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 2800363048; Mon, 9 Nov 2026 09:50:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9AB921F0089F; Mon, 9 Nov 2026 09:50:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794217829; bh=8jQST5+SfU/stcEn1VOV+s+O2grX/AjdmKJu3mY8h/o=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=OvHIGFuzeTrht0qsWVugipKYTrQLZcnvB6H9AoSgt/BfQa9OPyUvWqvJ8MOIsDadM GanFXxKFurEMX1AJqRVtXq3aRWMU3f5+WrFTpo5wgIB//RmeuK1DCmhhBP23ms4Q1h OxpyKGhtol4qDQfjdGC5xXV4KMT4/NcBlPfpG7uNWKEuNcRlrmaMThNfOOIhb6iqsV 6bvrPZ4Od2X8Yz8iIIBCfsyQcB4XJmpr+4JPhTB/o49dc/swkETYACw1k9TwnUEdPS i/WrVh9yir+LZOUj1ItLVGLUb1Oim+AfBYVUIRuwBzAMFlgA47kPNAltSH3lzQo+Vl sFPz+2VdU0FGg== Message-ID: <43fc45ff-8636-4961-a80a-29844c15d7a1@kernel.org> Date: Mon, 9 Nov 2026 10:49:08 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/5] mm: limit pagecache folio refcount when splicing into pipes From: "David Hildenbrand (Arm)" To: "Jose A. Perez de Azpillaga" , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Matthew Wilcox (Oracle)" , Jan Kara , Andrew Morton , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Matthew Brost , Joshua Hahn , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Peter Xu , Johannes Weiner , Song Liu , Rik van Riel , Miklos Szeredi , Alexander Viro , Christian Brauner , Hugh Dickins , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Arnd Bergmann , Jason Gunthorpe , Kevin Tian , "Joerg Roedel (AMD)" , Robin Murphy , Steve Sistare , John Hubbard , Josef Bacik Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.linux.dev, linux-arch@vger.kernel.org, iommu@lists.linux.dev, stable@vger.kernel.org References: <20261107-refcount_overflow_stable-v2-0-c38f6809b106@kernel.org> <20261107-refcount_overflow_stable-v2-2-c38f6809b106@kernel.org> <8d23b1eb-72aa-479d-9486-dbfd86d8414c@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: D99B040006 X-Stat-Signature: ydpje6xik4ijhx9iw97kppphqhopc7gh X-Rspam-User: 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=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1794217830-840224 X-HE-Meta: U2FsdGVkX1+7ablGUi57PBC2cAgIzuHlnzXIpO0Q3tlh0sMCfCn3AGcAlST0AoQ2ld6qFxVFwlbc4BFA3xiSshi2eIyymiEZFsXwZhYE2sagZo1F73cIhqPoUtS3FpRMPhE3928SBSiUS0NJ7By0V06IDGPyw5DLWjVh85N/HX2sIG3ltmGvj/zPgcv01fP20Wfxeu7FRAodM3izr22l+/FLb8Mk0MM4YIT4wOaMNxtiCyT9anchZTPy4vbIk04Me3NZM0o7sL5xSkAVQ4BWFhaPW6hXWxBL5JFct1O2py2QQhe9A1cBk3jgaDPJ+RPn9sBhRC/bifqRmBqVYaKmrG+8Agy/PeeAWvy4mlAWsPspy8zSLyC5kKMfMWiqb2o+6ZJLAv1XrXP8PKXvd9/4GCKC9tNVVqj8EGFOT+oU2818ijfmDPSW8XOP65thufYwoMybXyXXGbjPL1WmdiVTx+Th2i7mlFZrglyJi/2zXUjhTw5sHF+f9jmx7OWC6yGpzm9uQrJySOxID+kh/j1AprFoQpGAjtOC9uBLVSSBqm/u1fOH/VhkqIENAPWTBABVPOx+ZJJChfbuUK1NniI2ePTozYipygmbzA8fquaO8C89tKh3iqVuaV/u1GqLROg+5tFvWUn/6wEENzFBDFyotBshR2KkHm9YpIEras3PfZKKh8oPfolf6RrZ7dWkIvBrwt4FeS7hO93hvyzvucwbFbKt01beZe+mB5uaz5kvWk0UJr/aGQjJDObHCJM7qN0BjyN+pprtaYFM2GGtMAypYhyyfQKm3F1lFebJTZzpa5imMPl9clxFTb+WkCJPj4/oF+xCq1BPtXQXpjpkgup04+Hcl1EJuWjWWIMtaGnhFrzYIKivRcwf3j8ShtH9wGN26gFSR3gFHIO96mTdTYItdfjJCt1nAZNtTOaDBs+NcYh2V1kKxN1NtTZtWeFtOsezOzKjh833/CLlMPpb4rv TtaZtOqz NVeutXcfgZhig6z4R9+V9OPBK65o8Wb0mNsvvZSfOG/3yFVo7+mrNgFED1oOMpiTprRWn6ytR5oEKFutSvB3vWf5BmNHdL8OG2CwgIjR8umcp/nIB8ma9lqPglHXRrIlVDcLUWPBnOhm3sL7midMuWkTx0/1YXHk0oEpbJjeV09ZdEgFGtfPo9x84m49w2EFnrhT9zVVi9u5nlQOai/eCN/vPQ+iXvrVYI1r9q/ul0YyigQQEW7kzwThoQWVpxV9tuYvo3235ekWUeFyGgWJG+WVLMbXQuxCq3wmD9SCYk3noZxQ53LbOyxkmDDJfyzxEM+D/+6u8rlvvfoqqW50LK1+WzlAnSkQr4QE2bkmk4tl6rvs= 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 11/9/26 10:30, David Hildenbrand (Arm) wrote: > On 11/9/26 09:57, Jose A. Perez de Azpillaga wrote: >> On 11/7/26 11:23 PM, David Hildenbrand (Arm) wrote: >>> Similar to mapping pagecache folios into page tables, let's reject >>> additional references when splicing folios into a pipe if the refcount >>> is at its limit, similar to how we handle it during GUP. >>> >>> This will prevent more cases of possible folio refcount overflows with >>> large pagecache folios. >>> >>> Let's keep it simple and check in the two callers of >>> splice_folio_into_pipe(). Return -EOVERFLOW if the limit prevents any >>> progress, so do_splice_read() can fall back to copy_splice_read() when >>> read_iter is available. This keeps sendfile() and other splice users >>> working when ordinary reads would still succeed. >>> >>> Also fall back to copying in FUSE when taking another reference through >>> fuse_ref_folio() would exceed the limit. >>> >>> Also check in try_get_page() to cover pipe-buffer duplication by tee() >>> and partial pipe-to-pipe splicing. >>> >>> Fixes: 800d8c63b2e9 ("shmem: add huge pages support") >>> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") >>> Fixes: 793917d997df ("mm/readahead: Add large folio readahead") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: David Hildenbrand (Arm) >>> --- >>> fs/fuse/dev.c | 5 +++-- >>> fs/splice.c | 8 +++++++- >>> include/linux/mm.h | 9 ++++++--- >>> mm/filemap.c | 11 ++++++++--- >>> mm/shmem.c | 4 ++++ >>> 5 files changed, 28 insertions(+), 9 deletions(-) >>> >>> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c >>> index 3641abb90d6bb..4f6b7b42bfd3e 100644 >>> --- a/fs/fuse/dev.c >>> +++ b/fs/fuse/dev.c >>> @@ -1265,9 +1265,10 @@ int fuse_copy_folio(struct fuse_copy_state *cs, struct folio **foliop, >>> if (cs->write && cs->pipebufs && folio) { >>> /* >>> * Can't control lifetime of pipe buffers, so always >>> - * copy user pages. >>> + * copy user pages. Also copy folios at their refcount limit. >>> */ >>> - if (cs->req->args->user_pages) { >>> + if (cs->req->args->user_pages || >>> + unlikely(folio_ref_count_over_limit(folio))) { >>> err = fuse_copy_fill(cs); >>> if (err) >>> return err; >>> diff --git a/fs/splice.c b/fs/splice.c >>> index e6d43329ed3f0..df73a4e65118b 100644 >>> --- a/fs/splice.c >>> +++ b/fs/splice.c >>> @@ -956,6 +956,7 @@ static ssize_t do_splice_read(struct file *in, loff_t *ppos, >>> unsigned int flags) >>> { >>> unsigned int p_space; >>> + ssize_t ret; >>> >>> if (unlikely(!(in->f_mode & FMODE_READ))) >>> return -EBADF; >>> @@ -977,7 +978,12 @@ static ssize_t do_splice_read(struct file *in, loff_t *ppos, >>> */ >>> if ((in->f_flags & O_DIRECT) || IS_DAX(in->f_mapping->host)) >>> return copy_splice_read(in, ppos, pipe, len, flags); >>> - return in->f_op->splice_read(in, ppos, pipe, len, flags); >>> + ret = in->f_op->splice_read(in, ppos, pipe, len, flags); >>> + >>> + /* Fallback to copying when hitting folio refcount limits. */ >>> + if (unlikely(ret == -EOVERFLOW) && in->f_op->read_iter) >>> + ret = copy_splice_read(in, ppos, pipe, len, flags); >> >> here it can't tell where the -EOVERFLOW came from, if another file >> returns -EOVERFLOW (i.e. tty_fops uses copy_splice_read, and >> n_hdlc_tty_read() returns -EOVERFLOW after dropping the frame), it now >> gets a second read. > > > That's what claude told me during review, and when asked whether that actually > happened in practice it said no ;) > > So is that actually a problem? Double checked, claude managed to confuse itself. n_hdlc_tty_read() can indeed return -EOVERFLOW. I should just have let splice keep failing, dealing with copy fallback starts to get annoying. I guess switching to -ETOOMANYREFS should work (and might be a better fitting error) -- Cheers, David