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    SubjectRe: INFO: possible recursive locking detected: get_partial_node() on 3.2-rc1
    On Mon, Nov 14, 2011 at 01:34:13PM +0800, Shaohua Li wrote:
    > On Fri, 2011-11-11 at 23:02 +0800, Christoph Lameter wrote:
    > > On Fri, 11 Nov 2011, Shaohua Li wrote:
    > >
    > > > Looks this could be a real dead lock. we hold a lock to free a object,
    > > > but the free need allocate a new object. if the new object and the freed
    > > > object are from the same slab, there is a deadlock.
    > >
    > > unfreeze partials is never called when going through get_partial_node()
    > > so there is no deadlock AFAICT.
    > the unfreeze_partial isn't called from get_partial_node(). I thought the
    > code path is something like this: kmem_cache_free()->put_cpu_partial()
    > (hold lock) ->unfreeze_partials() ->discard_slab ->debug_object_init()
    > ->kmem_cache_alloc->get_partial_node()(hold lock). Not sure if this will
    > really happen, but looks like a deadlock.
    > But anyway, discard_slab() can be move out of unfreeze_partials()
    >
    > > > discard_slab() doesn't need hold the lock if the slab is already removed
    > > > from partial list. how about below patch, only compile tested.
    > >
    > > In general I think it is good to move the call to discard_slab() out from
    > > under the list_lock in unfreeze_partials(). Could you fold
    > > discard_page_list into unfreeze_partials()? __flush_cpu_slab still calls
    > > discard_page_list with disabled interrupts even after your patch.
    > I'm afraid there is alloc-in-atomic() error, but Yong & Julie's test
    > shows this is over thinking. Here is the updated patch. Yong & Julie, I
    > added your report/test by, because the new patch should be just like the
    > old one, but since I changed it a little bit, can you please have a
    > quick check? Thanks!
    >
    >
    >
    > Subject: slub: move discard_slab out of node lock
    >
    > Lockdep reports there is potential deadlock for slub node list_lock.
    > discard_slab() is called with the lock hold in unfreeze_partials(),
    > which could trigger a slab allocation, which could hold the lock again.
    >
    > discard_slab() doesn't need hold the lock actually, if the slab is
    > already removed from partial list.
    >
    > Reported-and-tested-by: Yong Zhang <yong.zhang0@gmail.com>
    > Reported-and-tested-by: Julie Sullivan <kernelmail.jms@gmail.com>
    > Signed-off-by: Shaohua Li <shaohua.li@intel.com>

    Tested-by: Yong Zhang <yong.zhang0@gmail.com>

    Thanks,
    Yong

    > ---
    > mm/slub.c | 16 ++++++++++++----
    > 1 file changed, 12 insertions(+), 4 deletions(-)
    >
    > Index: linux/mm/slub.c
    > ===================================================================
    > --- linux.orig/mm/slub.c 2011-11-11 16:17:39.000000000 +0800
    > +++ linux/mm/slub.c 2011-11-14 13:11:11.000000000 +0800
    > @@ -1862,7 +1862,7 @@ static void unfreeze_partials(struct kme
    > {
    > struct kmem_cache_node *n = NULL;
    > struct kmem_cache_cpu *c = this_cpu_ptr(s->cpu_slab);
    > - struct page *page;
    > + struct page *page, *discard_page = NULL;
    >
    > while ((page = c->partial)) {
    > enum slab_modes { M_PARTIAL, M_FREE };
    > @@ -1916,14 +1916,22 @@ static void unfreeze_partials(struct kme
    > "unfreezing slab"));
    >
    > if (m == M_FREE) {
    > - stat(s, DEACTIVATE_EMPTY);
    > - discard_slab(s, page);
    > - stat(s, FREE_SLAB);
    > + page->next = discard_page;
    > + discard_page = page;
    > }
    > }
    >
    > if (n)
    > spin_unlock(&n->list_lock);
    > +
    > + while (discard_page) {
    > + page = discard_page;
    > + discard_page = discard_page->next;
    > +
    > + stat(s, DEACTIVATE_EMPTY);
    > + discard_slab(s, page);
    > + stat(s, FREE_SLAB);
    > + }
    > }
    >
    > /*
    >
    >
    > --
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