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Date: Thu, 10 Nov 2016 15:16:45 +0100
From: Greg KH <greg@kroah.com>
To: Nicolai Stange <nicstange@gmail.com>
Cc: Mike Marshall <hubcap@omnibond.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Martin Brandenburg <martin@omnibond.com>
Subject: Re: debugfs question...
Message-ID: <20161110141645.GA20368@kroah.com>
References: <CAOg9mSSje9unMDnw9NhDd+cC=Ns9c+TK1fE2S0HytLU=HXYDpQ@mail.gmail.com>
 <20161031193823.GA11187@kroah.com>
 <87wpgoff0o.fsf@gmail.com>
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On Mon, Oct 31, 2016 at 09:19:03PM +0100, Nicolai Stange wrote:
> Hi,
> 
> Greg KH <greg@kroah.com> writes:
> 
> > On Mon, Oct 31, 2016 at 02:32:56PM -0400, Mike Marshall wrote:
> 
> >
> > [adding Nicolai to thread...]
> >
> 
> >> 
> >> Our debugfs code results in three files in /sys/kernel/debug/orangefs.
> >> One of the files gets deleted (debugfs_remove'd) and re-created
> >> (debugfs_create_file'd) the first time someone fires up the
> >> user-space part of Orangefs after a reboot.
> >> 
> >> We wondered what awful things might happen if someone was
> >> reading the file across the delete/re-create, so I wrote a
> >> program that opens the file, sleeps ten seconds and then
> >> starts reading, and I fired up the Orangefs userspace part
> >> during the sleep. I didn't see any problems there, we get
> >> EIO when the read happens.
> >> 
> >> But... really bad things happen if someone unloads the Orangefs
> >> module after my test program does the open and before the read
> >> starts. So I picked another debugfs-using-filesystem (f2fs) and
> >> pointed my tester-program at /sys/kernel/debug/f2fs/status, and
> >> the same bad thing happens there.
> 
> [...]
> 
> >> [ 1240.144316] Call Trace:
> >> [ 1240.144450]  [<ffffffff8122907f>] __fput+0xdf/0x1d0
> >> [ 1240.144704]  [<ffffffff812291ae>] ____fput+0xe/0x10
> >> [ 1240.144962]  [<ffffffff810b97de>] task_work_run+0x8e/0xc0
> >> [ 1240.145243]  [<ffffffff8109b98e>] do_exit+0x2ae/0xae0
> 
> 
> Thank you very much for this detailed report!
> 
> At least for the .../f2fs/status file, your splat at fput() can be
> readily explained with the full proxy's releaser not being protected
> against file removals in any way.
> 
> Partly this is on purpose, c.f. the comment in full_proxy_release().
> 
> However, I should have at least tried to acquire a reference to the
> owning module before accessing some static struct file_operations or
> even calling some ->release() within it. Meh.
> 
> The fix should be relatively trivial and I'll hopefully manage to
> submit a patch tomorrow.
> 
> May I add your (Mike Marshall's?) Reported-by?

Did this patch ever show up?