linux-kernel - Re: [git pull] gadgetfs fixes

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Message-ID: <20150315081733.GV29656@ZenIV.linux.org.uk>
Date:	Sun, 15 Mar 2015 08:17:34 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Alexander Holler <holler@...oftware.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: [git pull] gadgetfs fixes

On Sun, Mar 15, 2015 at 07:35:20AM +0100, Alexander Holler wrote:

> > Umm...  If I'm not misparsing what you said, you are talking about the
> 
> Glücklicherweise nicht. Vielleicht sollten wir es zur Abwechslung mal
> mit meiner bevorzugten Sprache versuchen.

Good.  I'll probably abstain from trying to mangle it, though.

Another question, if you don't mind - does that series (i.e. what's currently
in Linus' tree) fix the module refcount issues you'd been seeing?  I agree
with your analysis of likely cause (->f_op reassignments with different
->owner before and after) and these patches should have eliminated that, but
confirmation would be nice...

Incidentally, none of those file_operations need ->owner in the first place;
it doesn't hurt (as long as ->f_op doesn't change that way), but such files
(living on a filesystem provided by the module their methods are in)
don't need the module refcount bumped while the file is opened - having it
opened pins file_system_type of containing filesystem (by keeping a reference
to struct vfsmount, which keeps a reference to struct super_block, which keeps
a reference to file_system_type), so the module will be kept busy just fine.
Again, having ->owner on file_operations doesn't hurt, so it's not a bug
per se - just pointless in such cases.  So we might want to remove it
from ep_io_operations someday.  Anyway, that's a completely separate story...
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