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Message-ID: <20091123205732.GE6774@linux.vnet.ibm.com>
Date: Mon, 23 Nov 2009 12:57:32 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Pekka Enberg <penberg@...helsinki.fi>
Cc: Christoph Lameter <cl@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org,
mpm@...enic.com, LKML <linux-kernel@...r.kernel.org>,
Nick Piggin <npiggin@...e.de>
Subject: Re: lockdep complaints in slab allocator
On Mon, Nov 23, 2009 at 10:01:15PM +0200, Pekka Enberg wrote:
> On Mon, 2009-11-23 at 21:50 +0200, Pekka Enberg wrote:
> > On Mon, 23 Nov 2009, Pekka Enberg wrote:
> > > > That turns out to be _very_ hard. How about something like the following
> > > > untested patch which delays slab_destroy() while we're under nc->lock.
> >
> > On Mon, 2009-11-23 at 13:30 -0600, Christoph Lameter wrote:
> > > Code changes to deal with a diagnostic issue?
> >
> > OK, fair enough. If I suffer permanent brain damage from staring at the
> > SLAB code for too long, I hope you and Matt will chip in to pay for my
> > medication.
> >
> > I think I was looking at the wrong thing here. The problem is in
> > cache_free_alien() so the comment in slab_destroy() isn't relevant.
> > Looking at init_lock_keys() we already do special lockdep annotations
> > but there's a catch (as explained in a comment on top of
> > on_slab_alc_key):
> >
> > * We set lock class for alien array caches which are up during init.
> > * The lock annotation will be lost if all cpus of a node goes down and
> > * then comes back up during hotplug
> >
> > Paul said he was running CPU hotplug so maybe that explains the problem?
>
> Maybe something like this untested patch fixes the issue...
I will give it a go!
Thanx, Paul
> Pekka
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 7dfa481..84de47e 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -604,6 +604,26 @@ static struct kmem_cache cache_cache = {
>
> #define BAD_ALIEN_MAGIC 0x01020304ul
>
> +/*
> + * chicken and egg problem: delay the per-cpu array allocation
> + * until the general caches are up.
> + */
> +static enum {
> + NONE,
> + PARTIAL_AC,
> + PARTIAL_L3,
> + EARLY,
> + FULL
> +} g_cpucache_up;
> +
> +/*
> + * used by boot code to determine if it can use slab based allocator
> + */
> +int slab_is_available(void)
> +{
> + return g_cpucache_up >= EARLY;
> +}
> +
> #ifdef CONFIG_LOCKDEP
>
> /*
> @@ -620,40 +640,52 @@ static struct kmem_cache cache_cache = {
> static struct lock_class_key on_slab_l3_key;
> static struct lock_class_key on_slab_alc_key;
>
> -static inline void init_lock_keys(void)
> -
> +static void init_node_lock_keys(int q)
> {
> - int q;
> struct cache_sizes *s = malloc_sizes;
>
> - while (s->cs_size != ULONG_MAX) {
> - for_each_node(q) {
> - struct array_cache **alc;
> - int r;
> - struct kmem_list3 *l3 = s->cs_cachep->nodelists[q];
> - if (!l3 || OFF_SLAB(s->cs_cachep))
> - continue;
> - lockdep_set_class(&l3->list_lock, &on_slab_l3_key);
> - alc = l3->alien;
> - /*
> - * FIXME: This check for BAD_ALIEN_MAGIC
> - * should go away when common slab code is taught to
> - * work even without alien caches.
> - * Currently, non NUMA code returns BAD_ALIEN_MAGIC
> - * for alloc_alien_cache,
> - */
> - if (!alc || (unsigned long)alc == BAD_ALIEN_MAGIC)
> - continue;
> - for_each_node(r) {
> - if (alc[r])
> - lockdep_set_class(&alc[r]->lock,
> - &on_slab_alc_key);
> - }
> + if (g_cpucache_up != FULL)
> + return;
> +
> + for (s = malloc_sizes; s->cs_size != ULONG_MAX; s++) {
> + struct array_cache **alc;
> + struct kmem_list3 *l3;
> + int r;
> +
> + l3 = s->cs_cachep->nodelists[q];
> + if (!l3 || OFF_SLAB(s->cs_cachep))
> + return;
> + lockdep_set_class(&l3->list_lock, &on_slab_l3_key);
> + alc = l3->alien;
> + /*
> + * FIXME: This check for BAD_ALIEN_MAGIC
> + * should go away when common slab code is taught to
> + * work even without alien caches.
> + * Currently, non NUMA code returns BAD_ALIEN_MAGIC
> + * for alloc_alien_cache,
> + */
> + if (!alc || (unsigned long)alc == BAD_ALIEN_MAGIC)
> + return;
> + for_each_node(r) {
> + if (alc[r])
> + lockdep_set_class(&alc[r]->lock,
> + &on_slab_alc_key);
> }
> - s++;
> }
> }
> +
> +static inline void init_lock_keys(void)
> +{
> + int node;
> +
> + for_each_node(node)
> + init_node_lock_keys(node);
> +}
> #else
> +static void init_node_lock_keys(int q)
> +{
> +}
> +
> static inline void init_lock_keys(void)
> {
> }
> @@ -665,26 +697,6 @@ static inline void init_lock_keys(void)
> static DEFINE_MUTEX(cache_chain_mutex);
> static struct list_head cache_chain;
>
> -/*
> - * chicken and egg problem: delay the per-cpu array allocation
> - * until the general caches are up.
> - */
> -static enum {
> - NONE,
> - PARTIAL_AC,
> - PARTIAL_L3,
> - EARLY,
> - FULL
> -} g_cpucache_up;
> -
> -/*
> - * used by boot code to determine if it can use slab based allocator
> - */
> -int slab_is_available(void)
> -{
> - return g_cpucache_up >= EARLY;
> -}
> -
> static DEFINE_PER_CPU(struct delayed_work, reap_work);
>
> static inline struct array_cache *cpu_cache_get(struct kmem_cache *cachep)
> @@ -1254,6 +1266,8 @@ static int __cpuinit cpuup_prepare(long cpu)
> kfree(shared);
> free_alien_cache(alien);
> }
> + init_node_lock_keys(node);
> +
> return 0;
> bad:
> cpuup_canceled(cpu);
>
>
--
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