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Subject[PATCH] SLAB: Fix lockdep annotations for CPU hotplug
Date
As reported by Paul McKenney:

I am seeing some lockdep complaints in rcutorture runs that include
frequent CPU-hotplug operations. The tests are otherwise successful.
My first thought was to send a patch that gave each array_cache
structure's ->lock field its own struct lock_class_key, but you already
have a init_lock_keys() that seems to be intended to deal with this.

------------------------------------------------------------------------
=============================================
[ INFO: possible recursive locking detected ]
2.6.32-rc4-autokern1 #1
---------------------------------------------
syslogd/2908 is trying to acquire lock:
(&nc->lock){..-...}, at: [<c0000000001407f4>] .kmem_cache_free+0x118/0x2d4
but task is already holding lock:
(&nc->lock){..-...}, at: [<c0000000001411bc>] .kfree+0x1f0/0x324
other info that might help us debug this:
3 locks held by syslogd/2908:
#0: (&u->readlock){+.+.+.}, at: [<c0000000004556f8>] .unix_dgram_recvmsg+0x70/0x338
#1: (&nc->lock){..-...}, at: [<c0000000001411bc>] .kfree+0x1f0/0x324
#2: (&parent->list_lock){-.-...}, at: [<c000000000140f64>] .__drain_alien_cache+0x50/0xb8
stack backtrace:
Call Trace:
[c0000000e8ccafc0] [c0000000000101e4] .show_stack+0x70/0x184 (unreliable)
[c0000000e8ccb070] [c0000000000afebc] .validate_chain+0x6ec/0xf58
[c0000000e8ccb180] [c0000000000b0ff0] .__lock_acquire+0x8c8/0x974
[c0000000e8ccb280] [c0000000000b2290] .lock_acquire+0x140/0x18c
[c0000000e8ccb350] [c000000000468df0] ._spin_lock+0x48/0x70
[c0000000e8ccb3e0] [c0000000001407f4] .kmem_cache_free+0x118/0x2d4
[c0000000e8ccb4a0] [c000000000140b90] .free_block+0x130/0x1a8
[c0000000e8ccb540] [c000000000140f94] .__drain_alien_cache+0x80/0xb8
[c0000000e8ccb5e0] [c0000000001411e0] .kfree+0x214/0x324
[c0000000e8ccb6a0] [c0000000003ca860] .skb_release_data+0xe8/0x104
[c0000000e8ccb730] [c0000000003ca2ec] .__kfree_skb+0x20/0xd4
[c0000000e8ccb7b0] [c0000000003cf2c8] .skb_free_datagram+0x1c/0x5c
[c0000000e8ccb830] [c00000000045597c] .unix_dgram_recvmsg+0x2f4/0x338
[c0000000e8ccb920] [c0000000003c0f14] .sock_recvmsg+0xf4/0x13c
[c0000000e8ccbb30] [c0000000003c28ec] .SyS_recvfrom+0xb4/0x130
[c0000000e8ccbcb0] [c0000000003bfb78] .sys_recv+0x18/0x2c
[c0000000e8ccbd20] [c0000000003ed388] .compat_sys_recv+0x14/0x28
[c0000000e8ccbd90] [c0000000003ee1bc] .compat_sys_socketcall+0x178/0x220
[c0000000e8ccbe30] [c0000000000085d4] syscall_exit+0x0/0x40
This patch fixes the issue by setting up lockdep annotations during CPU
hotplug.

Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
---
mm/slab.c | 108 ++++++++++++++++++++++++++++++++++--------------------------
1 files changed, 61 insertions(+), 47 deletions(-)
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);
--
1.6.3.3


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