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Commit f14b488d authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'bpf-map-prealloc' 



Alexei Starovoitov says:

====================
bpf: map pre-alloc

v1->v2:
. fix few issues spotted by Daniel
. converted stackmap into pre-allocation as well
. added a workaround for lockdep false positive
. added pcpu_freelist_populate to be used by hashmap and stackmap

this path set switches bpf hash map to use pre-allocation by default
and introduces BPF_F_NO_PREALLOC flag to keep old behavior for cases
where full map pre-allocation is too memory expensive.

Some time back Daniel Wagner reported crashes when bpf hash map is
used to compute time intervals between preempt_disable->preempt_enable
and recently Tom Zanussi reported a dead lock in iovisor/bcc/funccount
tool if it's used to count the number of invocations of kernel
'*spin*' functions. Both problems are due to the recursive use of
slub and can only be solved by pre-allocating all map elements.

A lot of different solutions were considered. Many implemented,
but at the end pre-allocation seems to be the only feasible answer.
As far as pre-allocation goes it also was implemented 4 different ways:
- simple free-list with single lock
- percpu_ida with optimizations
- blk-mq-tag variant customized for bpf use case
- percpu_freelist
For bpf style of alloc/free patterns percpu_freelist is the best
and implemented in this patch set.
Detailed performance numbers in patch 3.
Patch 2 introduces percpu_freelist
Patch 1 fixes simple deadlocks due to missing recursion checks
Patch 5: converts stackmap to pre-allocation
Patches 6-9: prepare test infra
Patch 10: stress test for hash map infra. It attaches to spin_lock
functions and bpf_map_update/delete are called from different contexts
Patch 11: stress for bpf_get_stackid
Patch 12: map performance test

Reported-by: default avatarDaniel Wagner <daniel.wagner@bmw-carit.de>
Reported-by: default avatarTom Zanussi <tom.zanussi@linux.intel.com>
====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 8aba8b83 c3f85cff

include/linux/bpf.h

+6 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <uapi/linux/bpf.h>

#include <linux/workqueue.h>

#include <linux/file.h>

#include <linux/percpu.h>



struct bpf_map;
@@ -36,6 +37,7 @@ struct bpf_map { 
	u32 key_size;

	u32 value_size;

	u32 max_entries;

	u32 map_flags;

	u32 pages;

	struct user_struct *user;

	const struct bpf_map_ops *ops;
@@ -163,6 +165,8 @@ bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *f 
const struct bpf_func_proto *bpf_get_trace_printk_proto(void);



#ifdef CONFIG_BPF_SYSCALL

DECLARE_PER_CPU(int, bpf_prog_active);



void bpf_register_prog_type(struct bpf_prog_type_list *tl);

void bpf_register_map_type(struct bpf_map_type_list *tl);
@@ -175,6 +179,7 @@ struct bpf_map *__bpf_map_get(struct fd f); 
void bpf_map_inc(struct bpf_map *map, bool uref);

void bpf_map_put_with_uref(struct bpf_map *map);

void bpf_map_put(struct bpf_map *map);

int bpf_map_precharge_memlock(u32 pages);



extern int sysctl_unprivileged_bpf_disabled;
@@ -190,6 +195,7 @@ int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value, 
			   u64 flags);

int bpf_percpu_array_update(struct bpf_map *map, void *key, void *value,

			    u64 flags);

int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value);



/* memcpy that is used with 8-byte aligned pointers, power-of-8 size and

 * forced to use 'long' read/writes to try to atomically copy long counters.

include/uapi/linux/bpf.h

+3 −0
Original line number Diff line number Diff line
@@ -101,12 +101,15 @@ enum bpf_prog_type { 
#define BPF_NOEXIST	1 /* create new element if it didn't exist */

#define BPF_EXIST	2 /* update existing element */



#define BPF_F_NO_PREALLOC	(1U << 0)



union bpf_attr {

	struct { /* anonymous struct used by BPF_MAP_CREATE command */

		__u32	map_type;	/* one of enum bpf_map_type */

		__u32	key_size;	/* size of key in bytes */

		__u32	value_size;	/* size of value in bytes */

		__u32	max_entries;	/* max number of entries in a map */

		__u32	map_flags;	/* prealloc or not */

	};



	struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */

kernel/bpf/Makefile

+1 −1
Original line number Diff line number Diff line 
obj-y := core.o



obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o

obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o

obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o

ifeq ($(CONFIG_PERF_EVENTS),y)

obj-$(CONFIG_BPF_SYSCALL) += stackmap.o

endif

kernel/bpf/arraymap.c

+1 −1
Original line number Diff line number Diff line
@@ -53,7 +53,7 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr) 


	/* check sanity of attributes */

	if (attr->max_entries == 0 || attr->key_size != 4 ||

	    attr->value_size == 0)

	    attr->value_size == 0 || attr->map_flags)

		return ERR_PTR(-EINVAL);



	if (attr->value_size >= 1 << (KMALLOC_SHIFT_MAX - 1))

kernel/bpf/hashtab.c

+167 −73
Original line number Diff line number Diff line 
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com

 * Copyright (c) 2016 Facebook

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of version 2 of the GNU General Public
@@ -13,6 +14,7 @@ 
#include <linux/jhash.h>

#include <linux/filter.h>

#include <linux/vmalloc.h>

#include "percpu_freelist.h"



struct bucket {

	struct hlist_head head;
@@ -22,6 +24,8 @@ struct bucket { 
struct bpf_htab {

	struct bpf_map map;

	struct bucket *buckets;

	void *elems;

	struct pcpu_freelist freelist;

	atomic_t count;	/* number of elements in this hashtable */

	u32 n_buckets;	/* number of hash buckets */

	u32 elem_size;	/* size of each element in bytes */
@@ -29,15 +33,86 @@ struct bpf_htab { 


/* each htab element is struct htab_elem + key + value */

struct htab_elem {

	union {

		struct hlist_node hash_node;

		struct bpf_htab *htab;

		struct pcpu_freelist_node fnode;

	};

	struct rcu_head rcu;

	union {

	u32 hash;

		u32 key_size;

	};

	char key[0] __aligned(8);

};



static inline void htab_elem_set_ptr(struct htab_elem *l, u32 key_size,

				     void __percpu *pptr)

{

	*(void __percpu **)(l->key + key_size) = pptr;

}



static inline void __percpu *htab_elem_get_ptr(struct htab_elem *l, u32 key_size)

{

	return *(void __percpu **)(l->key + key_size);

}



static struct htab_elem *get_htab_elem(struct bpf_htab *htab, int i)

{

	return (struct htab_elem *) (htab->elems + i * htab->elem_size);

}



static void htab_free_elems(struct bpf_htab *htab)

{

	int i;



	if (htab->map.map_type != BPF_MAP_TYPE_PERCPU_HASH)

		goto free_elems;



	for (i = 0; i < htab->map.max_entries; i++) {

		void __percpu *pptr;



		pptr = htab_elem_get_ptr(get_htab_elem(htab, i),

					 htab->map.key_size);

		free_percpu(pptr);

	}

free_elems:

	vfree(htab->elems);

}



static int prealloc_elems_and_freelist(struct bpf_htab *htab)

{

	int err = -ENOMEM, i;



	htab->elems = vzalloc(htab->elem_size * htab->map.max_entries);

	if (!htab->elems)

		return -ENOMEM;



	if (htab->map.map_type != BPF_MAP_TYPE_PERCPU_HASH)

		goto skip_percpu_elems;



	for (i = 0; i < htab->map.max_entries; i++) {

		u32 size = round_up(htab->map.value_size, 8);

		void __percpu *pptr;



		pptr = __alloc_percpu_gfp(size, 8, GFP_USER | __GFP_NOWARN);

		if (!pptr)

			goto free_elems;

		htab_elem_set_ptr(get_htab_elem(htab, i), htab->map.key_size,

				  pptr);

	}



skip_percpu_elems:

	err = pcpu_freelist_init(&htab->freelist);

	if (err)

		goto free_elems;



	pcpu_freelist_populate(&htab->freelist, htab->elems, htab->elem_size,

			       htab->map.max_entries);

	return 0;



free_elems:

	htab_free_elems(htab);

	return err;

}



/* Called from syscall */

static struct bpf_map *htab_map_alloc(union bpf_attr *attr)

{
@@ -46,6 +121,10 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
	int err, i;

	u64 cost;



	if (attr->map_flags & ~BPF_F_NO_PREALLOC)

		/* reserved bits should not be used */

		return ERR_PTR(-EINVAL);



	htab = kzalloc(sizeof(*htab), GFP_USER);

	if (!htab)

		return ERR_PTR(-ENOMEM);
@@ -55,6 +134,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
	htab->map.key_size = attr->key_size;

	htab->map.value_size = attr->value_size;

	htab->map.max_entries = attr->max_entries;

	htab->map.map_flags = attr->map_flags;



	/* check sanity of attributes.

	 * value_size == 0 may be allowed in the future to use map as a set
@@ -92,7 +172,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
	if (percpu)

		htab->elem_size += sizeof(void *);

	else

		htab->elem_size += htab->map.value_size;

		htab->elem_size += round_up(htab->map.value_size, 8);



	/* prevent zero size kmalloc and check for u32 overflow */

	if (htab->n_buckets == 0 ||
@@ -112,6 +192,11 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 


	htab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;



	/* if map size is larger than memlock limit, reject it early */

	err = bpf_map_precharge_memlock(htab->map.pages);

	if (err)

		goto free_htab;



	err = -ENOMEM;

	htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct bucket),

				      GFP_USER | __GFP_NOWARN);
@@ -127,10 +212,16 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 
		raw_spin_lock_init(&htab->buckets[i].lock);

	}



	atomic_set(&htab->count, 0);

	if (!(attr->map_flags & BPF_F_NO_PREALLOC)) {

		err = prealloc_elems_and_freelist(htab);

		if (err)

			goto free_buckets;

	}



	return &htab->map;



free_buckets:

	kvfree(htab->buckets);

free_htab:

	kfree(htab);

	return ERR_PTR(err);
@@ -249,42 +340,42 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key) 
		}

	}



	/* itereated over all buckets and all elements */

	/* iterated over all buckets and all elements */

	return -ENOENT;

}





static inline void htab_elem_set_ptr(struct htab_elem *l, u32 key_size,

				     void __percpu *pptr)

{

	*(void __percpu **)(l->key + key_size) = pptr;

}



static inline void __percpu *htab_elem_get_ptr(struct htab_elem *l, u32 key_size)

static void htab_elem_free(struct bpf_htab *htab, struct htab_elem *l)

{

	return *(void __percpu **)(l->key + key_size);

}



static void htab_percpu_elem_free(struct htab_elem *l)

{

	free_percpu(htab_elem_get_ptr(l, l->key_size));

	if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH)

		free_percpu(htab_elem_get_ptr(l, htab->map.key_size));

	kfree(l);



}



static void htab_percpu_elem_free_rcu(struct rcu_head *head)

static void htab_elem_free_rcu(struct rcu_head *head)

{

	struct htab_elem *l = container_of(head, struct htab_elem, rcu);

	struct bpf_htab *htab = l->htab;



	htab_percpu_elem_free(l);

	/* must increment bpf_prog_active to avoid kprobe+bpf triggering while

	 * we're calling kfree, otherwise deadlock is possible if kprobes

	 * are placed somewhere inside of slub

	 */

	preempt_disable();

	__this_cpu_inc(bpf_prog_active);

	htab_elem_free(htab, l);

	__this_cpu_dec(bpf_prog_active);

	preempt_enable();

}



static void free_htab_elem(struct htab_elem *l, bool percpu, u32 key_size)

static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)

{

	if (percpu) {

		l->key_size = key_size;

		call_rcu(&l->rcu, htab_percpu_elem_free_rcu);

	if (!(htab->map.map_flags & BPF_F_NO_PREALLOC)) {

		pcpu_freelist_push(&htab->freelist, &l->fnode);

	} else {

		kfree_rcu(l, rcu);

		atomic_dec(&htab->count);

		l->htab = htab;

		call_rcu(&l->rcu, htab_elem_free_rcu);

	}

}
@@ -293,23 +384,39 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key, 
					 bool percpu, bool onallcpus)

{

	u32 size = htab->map.value_size;

	bool prealloc = !(htab->map.map_flags & BPF_F_NO_PREALLOC);

	struct htab_elem *l_new;

	void __percpu *pptr;



	if (prealloc) {

		l_new = (struct htab_elem *)pcpu_freelist_pop(&htab->freelist);

		if (!l_new)

			return ERR_PTR(-E2BIG);

	} else {

		if (atomic_inc_return(&htab->count) > htab->map.max_entries) {

			atomic_dec(&htab->count);

			return ERR_PTR(-E2BIG);

		}

		l_new = kmalloc(htab->elem_size, GFP_ATOMIC | __GFP_NOWARN);

		if (!l_new)

		return NULL;

			return ERR_PTR(-ENOMEM);

	}



	memcpy(l_new->key, key, key_size);

	if (percpu) {

		/* round up value_size to 8 bytes */

		size = round_up(size, 8);



		if (prealloc) {

			pptr = htab_elem_get_ptr(l_new, key_size);

		} else {

			/* alloc_percpu zero-fills */

		pptr = __alloc_percpu_gfp(size, 8, GFP_ATOMIC | __GFP_NOWARN);

			pptr = __alloc_percpu_gfp(size, 8,

						  GFP_ATOMIC | __GFP_NOWARN);

			if (!pptr) {

				kfree(l_new);

			return NULL;

				return ERR_PTR(-ENOMEM);

			}

		}



		if (!onallcpus) {
@@ -324,6 +431,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key, 
				off += size;

			}

		}

		if (!prealloc)

			htab_elem_set_ptr(l_new, key_size, pptr);

	} else {

		memcpy(l_new->key + round_up(key_size, 8), value, size);
@@ -336,12 +444,6 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key, 
static int check_flags(struct bpf_htab *htab, struct htab_elem *l_old,

		       u64 map_flags)

{

	if (!l_old && unlikely(atomic_read(&htab->count) >= htab->map.max_entries))

		/* if elem with this 'key' doesn't exist and we've reached

		 * max_entries limit, fail insertion of new elem

		 */

		return -E2BIG;



	if (l_old && map_flags == BPF_NOEXIST)

		/* elem already exists */

		return -EEXIST;
@@ -375,13 +477,6 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, 


	hash = htab_map_hash(key, key_size);



	/* allocate new element outside of the lock, since

	 * we're most likley going to insert it

	 */

	l_new = alloc_htab_elem(htab, key, value, key_size, hash, false, false);

	if (!l_new)

		return -ENOMEM;



	b = __select_bucket(htab, hash);

	head = &b->head;
@@ -394,21 +489,24 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, 
	if (ret)

		goto err;



	l_new = alloc_htab_elem(htab, key, value, key_size, hash, false, false);

	if (IS_ERR(l_new)) {

		/* all pre-allocated elements are in use or memory exhausted */

		ret = PTR_ERR(l_new);

		goto err;

	}



	/* add new element to the head of the list, so that

	 * concurrent search will find it before old elem

	 */

	hlist_add_head_rcu(&l_new->hash_node, head);

	if (l_old) {

		hlist_del_rcu(&l_old->hash_node);

		kfree_rcu(l_old, rcu);

	} else {

		atomic_inc(&htab->count);

		free_htab_elem(htab, l_old);

	}

	raw_spin_unlock_irqrestore(&b->lock, flags);

	return 0;

	ret = 0;

err:

	raw_spin_unlock_irqrestore(&b->lock, flags);

	kfree(l_new);

	return ret;

}
@@ -466,12 +564,11 @@ static int __htab_percpu_map_update_elem(struct bpf_map *map, void *key, 
	} else {

		l_new = alloc_htab_elem(htab, key, value, key_size,

					hash, true, onallcpus);

		if (!l_new) {

			ret = -ENOMEM;

		if (IS_ERR(l_new)) {

			ret = PTR_ERR(l_new);

			goto err;

		}

		hlist_add_head_rcu(&l_new->hash_node, head);

		atomic_inc(&htab->count);

	}

	ret = 0;

err:
@@ -489,7 +586,6 @@ static int htab_percpu_map_update_elem(struct bpf_map *map, void *key, 
static int htab_map_delete_elem(struct bpf_map *map, void *key)

{

	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);

	bool percpu = map->map_type == BPF_MAP_TYPE_PERCPU_HASH;

	struct hlist_head *head;

	struct bucket *b;

	struct htab_elem *l;
@@ -511,8 +607,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) 


	if (l) {

		hlist_del_rcu(&l->hash_node);

		atomic_dec(&htab->count);

		free_htab_elem(l, percpu, key_size);

		free_htab_elem(htab, l);

		ret = 0;

	}
@@ -531,17 +626,10 @@ static void delete_all_elements(struct bpf_htab *htab) 


		hlist_for_each_entry_safe(l, n, head, hash_node) {

			hlist_del_rcu(&l->hash_node);

			atomic_dec(&htab->count);

			if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH) {

				l->key_size = htab->map.key_size;

				htab_percpu_elem_free(l);

			} else {

				kfree(l);

			}

			htab_elem_free(htab, l);

		}

	}

}



/* Called when map->refcnt goes to zero, either from workqueue or from syscall */

static void htab_map_free(struct bpf_map *map)

{
@@ -554,10 +642,16 @@ static void htab_map_free(struct bpf_map *map) 
	 */

	synchronize_rcu();



	/* some of kfree_rcu() callbacks for elements of this map may not have

	 * executed. It's ok. Proceed to free residual elements and map itself

	/* some of free_htab_elem() callbacks for elements of this map may

	 * not have executed. Wait for them.

	 */

	rcu_barrier();

	if (htab->map.map_flags & BPF_F_NO_PREALLOC) {

		delete_all_elements(htab);

	} else {

		htab_free_elems(htab);

		pcpu_freelist_destroy(&htab->freelist);

	}

	kvfree(htab->buckets);

	kfree(htab);

}