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sea.source.kernel.org (Postfix) with ESMTP id 6033543A6E; Mon, 12 Jan 2026 13:34:42 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2B799C16AAE; Mon, 12 Jan 2026 13:34:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768224882; bh=2IWjz6hy9QWDfK8PS9oJROunKPChMHL7qfV31VPVLc4=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=Eub6fteqKg51fUIyfYVPjfhq/dGe6jfgS3PHv2l7MuA2WDBxKZKxgFa5iRUXrerE4 NCDfR5WTUYhS8J67WAWAmkd7wi8z2WBr/unFGD/j9A3HRlgZuYFxhDYeqpg/Y1bU6/ SVT4kUxc50g2D5vpTAtyIVlTS+as0gFRzWLZ02UbzUZeSu6J5eEbhGiEYd3lon2fp0 KkfaggLwX518zDD6XsrnqOlVeAdN0tJub+uJ3Abtv1Ckas/zTj5F1B2IkOKkCZ6Z03 RX8UGZkCCS9waUpnYfWVYwZWgUGVolplz9DFfjeEDAvXKx21pciDOX3tlhE3yfdLJM xsxcPK1mHfrww== Message-ID: Subject: Re: [PATCH 00/24] vfs: require filesystems to explicitly opt-in to lease support From: Jeff Layton To: Amir Goldstein , Christian Brauner , Chuck Lever Cc: Jan Kara , Luis de Bethencourt , Salah Triki , Nicolas Pitre , Christoph Hellwig , Anders Larsen , Alexander Viro , David Sterba , Chris Mason , Gao Xiang , Chao Yu , Yue Hu , Jeffle Xu , Sandeep Dhavale , Hongbo Li , Chunhai Guo , Jan Kara , Theodore Ts'o , Andreas Dilger , Jaegeuk Kim , OGAWA Hirofumi , David Woodhouse , Richard Weinberger , Dave Kleikamp , Ryusuke Konishi , Viacheslav Dubeyko , Konstantin Komarov , Mark Fasheh , Joel Becker , Joseph Qi , Mike Marshall , Martin Brandenburg , Miklos Szeredi , Phillip Lougher , Carlos Maiolino , Hugh Dickins , Baolin Wang , Andrew Morton , Namjae Jeon , Sungjong Seo , Yuezhang Mo , Chuck Lever , Alexander Aring , Andreas Gruenbacher , Jonathan Corbet , "Matthew Wilcox (Oracle)" , Eric Van Hensbergen , Latchesar Ionkov , Dominique Martinet , Christian Schoenebeck , Xiubo Li , Ilya Dryomov , Trond Myklebust , Anna Schumaker , Steve French , Paulo Alcantara , Ronnie Sahlberg , Shyam Prasad N , Tom Talpey , Bharath SM , Hans de Goede , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, jfs-discussion@lists.sourceforge.net, linux-nilfs@vger.kernel.org, ntfs3@lists.linux.dev, ocfs2-devel@lists.linux.dev, devel@lists.orangefs.org, linux-unionfs@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, gfs2@lists.linux.dev, linux-doc@vger.kernel.org, v9fs@lists.linux.dev, ceph-devel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, samba-technical@lists.samba.org Date: Mon, 12 Jan 2026 08:34:33 -0500 In-Reply-To: References: <20260108-setlease-6-20-v1-0-ea4dec9b67fa@kernel.org> <8af369636c32b868f83669c49aea708ca3b894ac.camel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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X-Rspamd-Queue-Id: AF20A1C000B X-Stat-Signature: n4b7xe7si7wcputii151g53i1xkmnyuw X-Rspam-User: X-HE-Tag: 1768224883-197595 X-HE-Meta: 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E/x2a+Y0uE7ONj4Z6RURkq+irtBM59Sy2ljajYdRqAL5cn5/M5B0ryWv3Uj3/Bu5DvCxfAkFgOUT+AZ4WRHZ9NiM6j//NwImevbtlrSQlC9+PlbzYoIsEzrd63lACWsVkZMdsCqkNrYfx8tw6Y610U3Mk+1nANb7eNxkUgZnScuqUuz4WUR23+ZF8ZtkVWA4dMKzol6TERlF9NWn3QBLWcZsLFJRnQAlVgE2AUTEb5jUn+63NBhXRpjOWHXXSSbvfP0kas1XlW80L3HxcASlJe7Ejscf4yanBE4enatkOCy7tt7kaVSNo48rSNg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 2026-01-09 at 19:52 +0100, Amir Goldstein wrote: > On Thu, Jan 8, 2026 at 7:57=E2=80=AFPM Jeff Layton w= rote: > >=20 > > On Thu, 2026-01-08 at 18:40 +0100, Jan Kara wrote: > > > On Thu 08-01-26 12:12:55, Jeff Layton wrote: > > > > Yesterday, I sent patches to fix how directory delegation support i= s > > > > handled on filesystems where the should be disabled [1]. That set i= s > > > > appropriate for v6.19. For v7.0, I want to make lease support be mo= re > > > > opt-in, rather than opt-out: > > > >=20 > > > > For historical reasons, when ->setlease() file_operation is set to = NULL, > > > > the default is to use the kernel-internal lease implementation. Thi= s > > > > means that if you want to disable them, you need to explicitly set = the > > > > ->setlease() file_operation to simple_nosetlease() or the equivalen= t. > > > >=20 > > > > This has caused a number of problems over the years as some filesys= tems > > > > have inadvertantly allowed leases to be acquired simply by having l= eft > > > > it set to NULL. It would be better if filesystems had to opt-in to = lease > > > > support, particularly with the advent of directory delegations. > > > >=20 > > > > This series has sets the ->setlease() operation in a pile of existi= ng > > > > local filesystems to generic_setlease() and then changes > > > > kernel_setlease() to return -EINVAL when the setlease() operation i= s not > > > > set. > > > >=20 > > > > With this change, new filesystems will need to explicitly set the > > > > ->setlease() operations in order to provide lease and delegation > > > > support. > > > >=20 > > > > I mainly focused on filesystems that are NFS exportable, since NFS = and > > > > SMB are the main users of file leases, and they tend to end up expo= rting > > > > the same filesystem types. Let me know if I've missed any. > > >=20 > > > So, what about kernfs and fuse? They seem to be exportable and don't = have > > > .setlease set... > > >=20 > >=20 > > Yes, FUSE needs this too. I'll add a patch for that. > >=20 > > As far as kernfs goes: AIUI, that's basically what sysfs and resctrl > > are built on. Do we really expect people to set leases there? > >=20 > > I guess it's technically a regression since you could set them on those > > sorts of files earlier, but people don't usually export kernfs based > > filesystems via NFS or SMB, and that seems like something that could be > > used to make mischief. > >=20 > > AFAICT, kernfs_export_ops is mostly to support open_by_handle_at(). See > > commit aa8188253474 ("kernfs: add exportfs operations"). > >=20 > > One idea: we could add a wrapper around generic_setlease() for > > filesystems like this that will do a WARN_ONCE() and then call > > generic_setlease(). That would keep leases working on them but we might > > get some reports that would tell us who's setting leases on these files > > and why. >=20 > IMO, you are being too cautious, but whatever. >=20 > It is not accurate that kernfs filesystems are NFS exportable in general. > Only cgroupfs has KERNFS_ROOT_SUPPORT_EXPORTOP. >=20 > If any application is using leases on cgroup files, it must be some > very advanced runtime (i.e. systemd), so we should know about the > regression sooner rather than later. >=20 I think so too. For now, I think I'll not bother with the WARN_ONCE(). Let's just leave kernfs out of the set until someone presents a real use-case. > There are also the recently added nsfs and pidfs export_operations. >=20 > I have a recollection about wanting to be explicit about not allowing > those to be exportable to NFS (nsfs specifically), but I can't see where > and if that restriction was done. >=20 > Christian? Do you remember? >=20 (cc'ing Chuck) FWIW, you can currently export and mount /sys/fs/cgroup via NFS. The directory doesn't show up when you try to get to it via NFSv4, but you can mount it using v3 and READDIR works. The files are all empty when you try to read them. I didn't try to do any writes. Should we add a mechanism to prevent exporting these sorts of filesystems? Even better would be to make nfsd exporting explicitly opt-in. What if we were to add a EXPORT_OP_NFSD flag that explicitly allows filesystems to opt-in to NFS exporting, and check for that in __fh_verify()? We'd have to add it to a bunch of existing filesystems, but that's fairly simple to do with an LLM. --=20 Jeff Layton