linux-kernel - Re: Yet another pipe related oops.

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Message-ID: <20130401203445.GA20862@ZenIV.linux.org.uk>
Date:	Mon, 1 Apr 2013 21:34:46 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: Yet another pipe related oops.

On Wed, Mar 27, 2013 at 05:45:06PM +0000, Al Viro wrote:
> We shouldn't, at least not for something that has been successfully
> opened.  I've a patch series cleaning that up a bit in the local
> queue; will check for bitrot and throw into for-next.

Egads...  OK, that has gone more than slightly out of control - right now
vfs.git#for-next is at 106 commits, -3.6KLoC balance and *still* hadn't
reached the ->f_op part of that work ;-/  OTOH, procfs-related code got
a lot cleaner and we actually have a chance to make the guts of proc_dir_entry
private to fs/proc now...  I'll cull the outright bug fixes into for-linus
and push it your way...

The thing that really worries me is debugfs; that fscker sets whatever
file_operations it's got from the driver that registered a file there
and sticks that into ->i_fop.  When we try to open() that, we get
try_module_get() ->i_fop->owner; so far, so good, but what if the driver
has just been removed *and* file_operations instance we are looking at
has already been freed?

IOW, how do we deal with a race between attempt to open a debugfs file and
its removal on driver unload?  Greg?
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