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Date: Sun, 10 Mar 2013 22:10:47 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dave Jones <davej@redhat.com>, Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: pipe_release oops.
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On Fri, Mar 08, 2013 at 10:30:01AM -0800, Linus Torvalds wrote:

> 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.

With OPEN_PATH we don't call ->open() (or anything in the driver, for that
matter) at all.  I really don't see how that could trigger...

> 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?

Back and looking through all that fun...