Messages in this thread | | | From | Linus Torvalds <> | Date | Tue, 24 May 2011 16:03:04 -0700 | Subject | Re: SLUB regression in current Linus |
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On Tue, May 24, 2011 at 4:52 AM, James Morris <jmorris@namei.org> wrote: > > Reverting the patch appears to fix the hang for me, although I'm not sure > what the actual problem is. > > This is on a quad-core Opteron (1352). Let me know if you need any further > info.
That whole "deactivate_slab()" + "c->page = NULL" that that patch does looks bogus.
Look at __slab_alloc: we have:
page = c->page; if (!page) goto new_slab;
slab_lock(page); if (unlikely(!node_match(c, node))) goto another_slab;
and let's assume we have two users racing on that "c->page". The "slab_lock()" is going to work for one of them, right?
Ok, so the one it works for will then hit
if (kmem_cache_debug(s)) goto debug;
and thus get to the new "deactivate_slab(s,c) + c->page = NULL" and then unlock the page.
In the meantime, the one that wasn't able to lock the page will now go forward, but will not have "node_match()" any more, so it does that "goto another_slab".
Which does "deactivate_slab(s,c)" again, and now c->page is NULL, so that totally breaks.
What am I missing?
That patch seems to be just broken piece-of-s%^!
Christoph, Pekka, please tell me why I shouldn't immediately revert it. What am I missing?
Linus
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