linux-kernel - Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked

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Message-ID: <20230914192331.GK800259@ZenIV>
Date:   Thu, 14 Sep 2023 20:23:31 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Christian Brauner <brauner@...nel.org>
Cc:     Christoph Hellwig <hch@....de>, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Tejun Heo <tj@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Damien Le Moal <dlemoal@...nel.org>,
        Naohiro Aota <naohiro.aota@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-hardening@...r.kernel.org,
        cgroups@...r.kernel.org, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 03/19] fs: release anon dev_t in deactivate_locked_super

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 ;-/