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    SubjectRe: SLOB lockup (was: Re: [tip:core/locking] lockdep: annotate reclaim context (__GFP_NOFS), fix SLOB)
    On Sun, 15 Mar 2009, Nick Piggin wrote:
    > On Sunday 15 March 2009 20:47:04 Ingo Molnar wrote:
    > > * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
    > > > On Sunday 15 March 2009 17:48:18 Ingo Molnar wrote:
    > > > > > Cc: Nick Piggin <npiggin@suse.de>
    > > > > > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > > > > > LKML-Reference: <20090128135457.350751756@chello.nl>
    > > > > > Signed-off-by: Ingo Molnar <mingo@elte.hu>
    > > > >
    > > > > and with this fixed, and with SLOB now being tested in -tip, the
    > > > > new lockdep assert attached below (followed by a real lockup)
    > > > > pops up.
    > > > >
    > > > > Seems like a genuine SLOB bug, probably present upstream as
    > > > > well.
    > > >
    > > > Hmmf. debugobjects calls back into the slab allocator from the
    > > > page allocator. The following patch would improve SLOB, but I
    > > > think it would be a good idea to avoid a dependency in that
    > > > direction. Can debugobjects defer this freeing?
    > >
    > > dunno - that's a question for Thomas.
    >
    > Well I think it could, and it should (just add them to a list and
    > kick off a workqueue or something). It is not a good idea for
    > fringe debug functionality like this to introduce such a connection
    > between core code like this. Unless there is a *really* good reason.
    >
    > Apart from the locking issue, I wonder if the recursion is bounded?

    Yes. debugobject free does not call back into debugobjects, but you
    are right it should defer the free. I have rcu based deferred free in
    -rt for the very same reason. I'll whip up a solution for mainline as
    well.

    Thanks,

    tglx


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