Re: [patch 0/6] 3.14-rt1 fixes

[Nicholas Mc Guire <der.herr@hofr.at>]

On Sat, 03 May 2014, Mike Galbraith wrote:

> On Sat, 2014-05-03 at 14:31 +0200, Nicholas Mc Guire wrote: 
> > On Sat, 03 May 2014, Mike Galbraith wrote:
> 
> > > If this is in fact safe, you should be able to move each and every
> > > migrate_disable() to post acquisition.
> > 
> > yup
> 
> Having just seen working -> brick transition, color me skeptical.
> 
> > > I have a virtual nickle that
> > > says your box will have a severe allergic reaction to such a patch.
> > >
> > Actually that is what the pushdowns in the read_lock/write_lock api did and
> > I did not notice any of the systems having problems with that.
> 
> If you had tested hotplug, you would have met the deadlock, and would
> have verified that the change to read_lock() was the culprit instead of
> me doing that.  Steven also verified that.  You too can flip back and
> forth, drive boxen into the wall as many times as it take to convince
> yourself that that change really really did induce the breakage.
>

I did not test hotplug - I did try and understand the code to
verify the assumptions - but before looking at details of some code
path (which in my opinion has a few problems of its own) I think it
would be best to clarify first if the assumptions made for the
migrate pushdown patches is right or not - if it is not there is no point
in discussing individual code paths but then that patch set simply needs to 
go out, if the assumptions are right then we can discuss where the fix is 
needed.

thx!
hofrat