linux-kernel - Re: pipe

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Date:	Fri, 8 Mar 2013 10:30:01 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: pipe_release oops.

On Fri, Mar 8, 2013 at 6:53 AM, Dave Jones <davej@...hat.com> wrote:
>
> Yeah, that does the trick.
> I changed your other diff a little to use a goto, which reduces a level of indentation..

Hmm. So I've been trying to figure this out, and I really don't see
it. Every single pipe open routine *should* make sure that the inode
has an inode->i_pipe field. So if the open() has succeeded and you
have a valid file descriptor, the inode->i_pipe thing should be there.

I must be missing something, and I wonder if the thing I'm missing is
that with OPEN_PATH we may now have open calls that don't actually
have FMODE_READ or FMODE_WRITE set at all.

So suddenly we end up with these pipe openers that don't update the
counts, and I could imagine that really confusing us...

So I'm wondering if you could apply this patch, and see if that
triggers. In fact, please un-apply the other changes to fs/pipe.c too,
to see if it also obviates the need for checking i_pipe for NULL. You
should get the new warning (once), but you should not get any oopses..

Anyway, this would explain why the actual read/write paths don't need
to check for i_pipe - if FMODE_READ/WRITE aren't set, we'll never get
that far. But the release() and the fasync functions do get called
even for non-readable and non-writable files...

And Al, please get your email fixed. Is somebody usually on irc with
him or something?

                  Linus

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