linux-kernel - Re: [PATCH v2 62/67] nfs: Convert to new fscache volume/cookie API

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Message-ID: <353628.1639229864@warthog.procyon.org.uk>
Date:   Sat, 11 Dec 2021 13:37:44 +0000
From:   David Howells <dhowells@...hat.com>
To:     David Wysochanski <dwysocha@...hat.com>
Cc:     dhowells@...hat.com, linux-cachefs <linux-cachefs@...hat.com>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        linux-nfs <linux-nfs@...r.kernel.org>,
        Trond Myklebust <trondmy@...merspace.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Omar Sandoval <osandov@...ndov.com>,
        JeffleXu <jefflexu@...ux.alibaba.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-afs@...ts.infradead.org,
        linux-cifs <linux-cifs@...r.kernel.org>,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 62/67] nfs: Convert to new fscache volume/cookie API

David Wysochanski <dwysocha@...hat.com> wrote:

> >  (4) fscache_enable/disable_cookie() have been removed.
> >
> >      Call fscache_use_cookie() and fscache_unuse_cookie() when a file is
> >      opened or closed to prevent a cache file from being culled and to keep
> >      resources to hand that are needed to do I/O.
> >
> >      Unuse the cookie when a file is opened for writing.  This is gated by
> >      the NFS_INO_FSCACHE flag on the nfs_inode.
> >
> >      A better way might be to invalidate it with FSCACHE_INVAL_DIO_WRITE
> >      which will keep it unused until all open files are closed.
> >
> 
> It looks like the comment doesn't match what was actually done inside
> nfs_fscache_open_file().  Is the code right and the comment just out of date?

The comment is out of date.  NFS_INO_FSCACHE isn't used now.

> I'm getting that kasan UAF firing periodically in this code path, and so it
> looks related to this change,though I don't have great info on it so far and
> it's hard to reproduce.

Can you copy the kasan UAF text into a reply?

David