Re: [patch 1/3] ipc/sem: fix -rt livelock

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On Fri, 2013-10-04 at 16:02 +0200, Manfred Spraul wrote: 
> On 10/04/2013 03:55 PM, Mike Galbraith wrote:
> > On Fri, 2013-10-04 at 13:28 +0200, Sebastian Andrzej Siewior wrote:
> >> On 10/04/2013 01:16 PM, Mike Galbraith wrote:
> >>> Manfred's race fix also kills loop, and thereby the -rt livelock, so the
> >>> only question is does -rt want to use his completion wakeup scheme, and
> >>> does it want to do something about spin_unlock_wait() unconditionally
> >>> grabbing/releasing every lock in the array.
> >> So his patches went into v3.11 or so right? So all -RT released post
> >> this point will have it fixed right?
> > Most fixes have gone into master.  There's still at least one in the
> > pipe, ipc/sem.c: synchronize semop and semctl with IPC_RMID, and I
> > _think_ there's still one open issue.
> >
> > <quoting Manfred>
> > And now new:
> > 1) ipc/namespace.c:
> >       free_ipcs() still assumes the "old style" free calls:
> >       rcu_lock and ipc_lock dropped within the callback.
> >
> >       freeary() was converted - but free_ipcs was not updated.
> >
> >       Thus:
> >       Closing a namespace with sem arrays and threads that are waiting
> > on
> > the array with semtimedop() and bad timing can deadlock the semtimedop
> > thread.
> >       (i.e.: spin_lock() waiting forever).
> > </quoting Manfred>
> That one was a false alarm, i.e. everything is fixed in -mm.

Cool, that works out rather nicely.  I looked at fixing it, and couldn't
figure out what the heck was wrong with it :)

-Mike

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