Re: bug fix patch lost: git problem or just incorrect merge?

From: James Bottomley
Date: Fri May 21 2010 - 13:23:35 EST

On Fri, 2010-05-21 at 10:04 -0700, Linus Torvalds wrote:
> On Fri, 21 May 2010, Linus Torvalds wrote:
> >
> > > Either way, of course, we need the patch back ...
> >
> > I'll fix it up.
> Hmm. Pushed that out as appended, since that is the correct resolve.


> HOWEVER - the code still doesn't actually make any sense. It does
> if (sk_sleep(sock->sk)) {
> and that sk_sleep() today is an inline function that just does
> return &sk->sk_wq->wait;
> and testing the result of an address-of operation for NULL is almost
> certainly totally non-sensical. Sure, it _might_ work (maybe 'wait' is the
> first element in the 'sk_wq' data structure, and sk_wq is NULL), but that
> kind of code is always total and utterl crap regardless.
> So I pushed it out because I had done the resolve already, and it's no
> worse than it was before, but it's still a steaming buggy pile of shit.

Yes, the problem was caused by this patch

commit 43815482370c510c569fd18edb57afcb0fa8cab6
Author: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Date: Thu Apr 29 11:01:49 2010 +0000

net: sock_def_readable() and friends RCU conversion

Which moved sk_sleep() from returning the pointer to the waitqueue,
which may or may not be assigned to returning a pointer to an internal
waitqueue in the socket, which, obviously, can never be null.

I suspect what iscsi should be doing is always sending the wakeup ... in
which case with your resolution, the code is operating correctly even if
the form is suboptimal.

> It being iscsi, I can't bring myself to care. But somebody who does,
> should really look at it. The most likely resolution is to remove the test
> entirely, since I don't think it's ever valid to have a socket that
> doesn't have a sk_wq (there's a _lot_ of unconditional use of sk_sleep()).

I'll have Mike look at it, but I think just removing the if() will be
the correct resolution.


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