From: Alexei Starovoitov <ast@xxxxxxxxxx>
kmalloc_nolock() can be called from any context
the ___slab_alloc() can acquire local_trylock_t (which is rt_spin_lock
in PREEMPT_RT) and attempt to acquire a different local_trylock_t
while in the same task context.
The calling sequence might look like:
kmalloc() -> tracepoint -> bpf -> kmalloc_nolock()
or more precisely:
__lock_acquire+0x12ad/0x2590
lock_acquire+0x133/0x2d0
rt_spin_lock+0x6f/0x250
___slab_alloc+0xb7/0xec0
kmalloc_nolock_noprof+0x15a/0x430
my_debug_callback+0x20e/0x390 [testmod]
___slab_alloc+0x256/0xec0
__kmalloc_cache_noprof+0xd6/0x3b0
Make LOCKDEP understand that local_trylock_t-s protect
different kmem_caches. In order to do that add lock_class_key
for each kmem_cache and use that key in local_trylock_t.
This stack trace is possible on both PREEMPT_RT and !PREEMPT_RT,
but teach lockdep about it only for PREEMPT_RT, since
in !PREEMPT_RT the ___slab_alloc() code is using
local_trylock_irqsave() when lockdep is on.
Note, this patch applies this logic to local_lock_t
while the next one converts it to local_trylock_t.
Both are mapped to rt_spin_lock in PREEMPT_RT.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
mm/slab.h | 1 +
mm/slub.c | 20 ++++++++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/mm/slab.h b/mm/slab.h
index f1866f2d9b21..5a6f824a282d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -234,6 +234,7 @@ struct kmem_cache_order_objects {
struct kmem_cache {
#ifndef CONFIG_SLUB_TINY
struct kmem_cache_cpu __percpu *cpu_slab;
+ struct lock_class_key lock_key;
#endif
struct slub_percpu_sheaves __percpu *cpu_sheaves;
/* Used for retrieving partial slabs, etc. */
diff --git a/mm/slub.c b/mm/slub.c
index bf399ba65a4b..212161dc0f29 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3591,12 +3591,29 @@ static inline void note_cmpxchg_failure(const char *n,
static void init_kmem_cache_cpus(struct kmem_cache *s)
{
+#ifdef CONFIG_PREEMPT_RT
+ /*
+ * Register lockdep key for non-boot kmem caches to avoid
+ * WARN_ON_ONCE(static_obj(key))) in lockdep_register_key()
+ */
+ bool finegrain_lockdep = !init_section_contains(s, 1);
+#else
+ /*
+ * Don't bother with different lockdep classes for each
+ * kmem_cache, since we only use local_trylock_irqsave().
+ */
+ bool finegrain_lockdep = false;
+#endif
int cpu;
struct kmem_cache_cpu *c;
+ if (finegrain_lockdep)
+ lockdep_register_key(&s->lock_key);
for_each_possible_cpu(cpu) {
c = per_cpu_ptr(s->cpu_slab, cpu);
local_lock_init(&c->lock);
+ if (finegrain_lockdep)
+ lockdep_set_class(&c->lock, &s->lock_key);
c->tid = init_tid(cpu);
}
}
@@ -7142,6 +7159,9 @@ void __kmem_cache_release(struct kmem_cache *s)
if (s->cpu_sheaves)
pcs_destroy(s);
#ifndef CONFIG_SLUB_TINY
+#ifdef CONFIG_PREEMPT_RT
+ lockdep_unregister_key(&s->lock_key);
+#endif
free_percpu(s->cpu_slab);
#endif
free_kmem_cache_nodes(s);
--
2.47.3
