Commit 83382af9 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Vlastimil Babka
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slab: Make slub local_(try)lock more precise for LOCKDEP 



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: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
parent d7242af8

mm/slab.h

+1 −0
Original line number Diff line number Diff line
@@ -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. */

mm/slub.c

+20 −0
Original line number Diff line number Diff line
@@ -3586,12 +3586,29 @@ 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);

	}

}
@@ -7210,6 +7227,9 @@ 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);