linux-kernel - Re: nbd locking problems

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Date:	Sat, 29 Jan 2011 00:11:53 +0100
From:	Soren Hansen <soren@...ux2go.dk>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	linux-kernel@...r.kernel.org, Dave Hansen <haveblue@...ibm.com>
Subject: Re: nbd locking problems

2011/1/28 Serge E. Hallyn <serge@...lyn.com>:
> Thanks for looking into this, Soren.

Sure :)

> As Dave just explained to me, BKL is released when you sleep :)

Ah, yes, that makes perfect sense.

> I assume that's how it gets released around the kthread_create().  I
> *think* you're right that the new mutex is superfluous, but I'd like to
> look through the ioctl code and make sure there's no shared state which
> we need to protect.

Yup, I've tried that and I didn't find anything, but this is very new
territory to me, so more eyes sounds great.

> I don't see how there could be, or rather, if there
> were, then it was broken before.

Good point.

> In the meantime, could you please post your patch?  (Is it the
> three-liner I'd expect?)

Indeed it is. I was holding off on posting it, because I was hoping
Pavel Machek would chime in. Pavel's commit message in [1] suggested
that there was more work to do before the BKL could be vanquished from
this driver (by changing .ioctl to .unlocked_ioctl).

I guess it can't hurt to post it, though. I'll do that in a second.

[1]: 1a2ad21128bb4eb79f3c05e5801edcc5ed3ef1d3

-- 
Soren Hansen        | http://linux2go.dk/
Ubuntu Developer    | http://www.ubuntu.com/
OpenStack Developer | http://www.openstack.org/
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