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Date:   Thu, 14 Sep 2023 20:23:31 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Christian Brauner <brauner@kernel.org>
Cc:     Christoph Hellwig <hch@lst.de>, Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Reinette Chatre <reinette.chatre@intel.com>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
        Tejun Heo <tj@kernel.org>,
        Trond Myklebust <trond.myklebust@hammerspace.com>,
        Anna Schumaker <anna@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Damien Le Moal <dlemoal@kernel.org>,
        Naohiro Aota <naohiro.aota@wdc.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org,
        linux-nfs@vger.kernel.org, linux-hardening@vger.kernel.org,
        cgroups@vger.kernel.org, Jan Kara <jack@suse.cz>
Subject: Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked_super
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Sender: Al Viro <viro@ftp.linux.org.uk>
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On Thu, Sep 14, 2023 at 05:58:05PM +0100, Al Viro wrote:

> Incidentally, I'm going to add a (belated by 10 years) chunk in porting.rst
> re making sure that anything in superblock that might be needed by methods
> called in RCU mode should *not* be freed without an RCU delay...  Should've
> done that back in 3.12 merge window when RCU'd vfsmounts went in; as it
> is, today we have several filesystems with exact same kind of breakage.
> hfsplus and affs breakage had been there in 3.13 (missed those two), exfat
> and ntfs3 - introduced later, by initial merges of filesystems in question.
> Missed on review...
> 
> Hell knows - perhaps Documentation/filesystems/whack-a-mole might be a good
> idea...

Actually, utf8 casefolding stuff also has the same problem, so ext4 and f2fs
with casefolding are also affected ;-/