Merge branch 'bpf-allocator'

Alexei Starovoitov says:

====================
Introduce any context BPF specific memory allocator.

Tracing BPF programs can attach to kprobe and fentry. Hence they run in
unknown context where calling plain kmalloc() might not be safe. Front-end
kmalloc() with per-cpu cache of free elements. Refill this cache asynchronously
from irq_work.

Major achievements enabled by bpf_mem_alloc:
- Dynamically allocated hash maps used to be 10 times slower than fully
  preallocated. With bpf_mem_alloc and subsequent optimizations the speed
  of dynamic maps is equal to full prealloc.
- Tracing bpf programs can use dynamically allocated hash maps. Potentially
  saving lots of memory. Typical hash map is sparsely populated.
- Sleepable bpf programs can used dynamically allocated hash maps.

Future work:
- Expose bpf_mem_alloc as uapi FD to be used in dynptr_alloc, kptr_alloc
- Convert lru map to bpf_mem_alloc
- Further cleanup htab code. Example: htab_use_raw_lock can be removed.

Changelog:

v5->v6:
- Debugged the reason for selftests/bpf/test_maps ooming in a small VM that BPF CI is using.
  Added patch 16 that optimizes the usage of rcu_barrier-s between bpf_mem_alloc and
  hash map. It drastically improved the speed of htab destruction.

v4->v5:
- Fixed missing migrate_disable in hash tab free path (Daniel)
- Replaced impossible "memory leak" with WARN_ON_ONCE (Martin)
- Dropped sysctl kernel.bpf_force_dyn_alloc patch (Daniel)
- Added Andrii's ack
- Added new patch 15 that removes kmem_cache usage from bpf_mem_alloc.
  It saves memory, speeds up map create/destroy operations
  while maintains hash map update/delete performance.

v3->v4:
- fix build issue due to missing local.h on 32-bit arch
- add Kumar's ack
- proposal for next steps from Delyan:
https://lore.kernel.org/bpf/d3f76b27f4e55ec9e400ae8dcaecbb702a4932e8.camel@fb.com/

v2->v3:
- Rewrote the free_list algorithm based on discussions with Kumar. Patch 1.
- Allowed sleepable bpf progs use dynamically allocated maps. Patches 13 and 14.
- Added sysctl to force bpf_mem_alloc in hash map even if pre-alloc is
  requested to reduce memory consumption. Patch 15.
- Fix: zero-fill percpu allocation
- Single rcu_barrier at the end instead of each cpu during bpf_mem_alloc destruction

v2 thread:
https://lore.kernel.org/bpf/20220817210419.95560-1-alexei.starovoitov@gmail.com/

v1->v2:
- Moved unsafe direct call_rcu() from hash map into safe place inside bpf_mem_alloc. Patches 7 and 9.
- Optimized atomic_inc/dec in hash map with percpu_counter. Patch 6.
- Tuned watermarks per allocation size. Patch 8
- Adopted this approach to per-cpu allocation. Patch 10.
- Fully converted hash map to bpf_mem_alloc. Patch 11.
- Removed tracing prog restriction on map types. Combination of all patches and final patch 12.

v1 thread:
https://lore.kernel.org/bpf/20220623003230.37497-1-alexei.starovoitov@gmail.com/

LWN article:
https://lwn.net/Articles/899274/
====================

Link: https://lore.kernel.org/r/Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/linux/bpf_mem_alloc.h

+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
+#ifndef _BPF_MEM_ALLOC_H
+#define _BPF_MEM_ALLOC_H
+#include <linux/compiler_types.h>
+#include <linux/workqueue.h>
+
+struct bpf_mem_cache;
+struct bpf_mem_caches;
+
+struct bpf_mem_alloc {
+	struct bpf_mem_caches __percpu *caches;
+	struct bpf_mem_cache __percpu *cache;
+	struct work_struct work;
+};
+
+int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu);
+void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma);
+
+/* kmalloc/kfree equivalent: */
+void *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size);
+void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr);
+
+/* kmem_cache_alloc/free equivalent: */
+void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma);
+void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr);
+
+#endif /* _BPF_MEM_ALLOC_H */

kernel/bpf/Makefile

@@ -13,7 +13,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
 obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o
 obj-$(CONFIG_BPF_JIT) += trampoline.o
-obj-$(CONFIG_BPF_SYSCALL) += btf.o
+obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o
 obj-$(CONFIG_BPF_JIT) += dispatcher.o
 ifeq ($(CONFIG_NET),y)
 obj-$(CONFIG_BPF_SYSCALL) += devmap.o

kernel/bpf/hashtab.c

@@ -14,6 +14,7 @@
 #include "percpu_freelist.h"
 #include "bpf_lru_list.h"
 #include "map_in_map.h"
+#include <linux/bpf_mem_alloc.h>
 
 #define HTAB_CREATE_FLAG_MASK						\
 	(BPF_F_NO_PREALLOC | BPF_F_NO_COMMON_LRU | BPF_F_NUMA_NODE |	\
@@ -92,6 +93,8 @@ struct bucket {
 
 struct bpf_htab {
 	struct bpf_map map;
+	struct bpf_mem_alloc ma;
+	struct bpf_mem_alloc pcpu_ma;
 	struct bucket *buckets;
 	void *elems;
 	union {
@@ -99,7 +102,12 @@ struct bpf_htab {
 		struct bpf_lru lru;
 	};
 	struct htab_elem *__percpu *extra_elems;
-	atomic_t count;	/* number of elements in this hashtable */
+	/* number of elements in non-preallocated hashtable are kept
+	 * in either pcount or count
+	 */
+	struct percpu_counter pcount;
+	atomic_t count;
+	bool use_percpu_counter;
 	u32 n_buckets;	/* number of hash buckets */
 	u32 elem_size;	/* size of each element in bytes */
 	u32 hashrnd;
@@ -114,14 +122,14 @@ struct htab_elem {
 		struct {
 			void *padding;
 			union {
-				struct bpf_htab *htab;
 				struct pcpu_freelist_node fnode;
 				struct htab_elem *batch_flink;
 			};
 		};
 	};
 	union {
-		struct rcu_head rcu;
+		/* pointer to per-cpu pointer */
+		void *ptr_to_pptr;
 		struct bpf_lru_node lru_node;
 	};
 	u32 hash;
@@ -441,8 +449,6 @@ static int htab_map_alloc_check(union bpf_attr *attr)
 	bool zero_seed = (attr->map_flags & BPF_F_ZERO_SEED);
 	int numa_node = bpf_map_attr_numa_node(attr);
 
-	BUILD_BUG_ON(offsetof(struct htab_elem, htab) !=
-		     offsetof(struct htab_elem, hash_node.pprev));
 	BUILD_BUG_ON(offsetof(struct htab_elem, fnode.next) !=
 		     offsetof(struct htab_elem, hash_node.pprev));
 
@@ -563,6 +569,29 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 
 	htab_init_buckets(htab);
 
+/* compute_batch_value() computes batch value as num_online_cpus() * 2
+ * and __percpu_counter_compare() needs
+ * htab->max_entries - cur_number_of_elems to be more than batch * num_online_cpus()
+ * for percpu_counter to be faster than atomic_t. In practice the average bpf
+ * hash map size is 10k, which means that a system with 64 cpus will fill
+ * hashmap to 20% of 10k before percpu_counter becomes ineffective. Therefore
+ * define our own batch count as 32 then 10k hash map can be filled up to 80%:
+ * 10k - 8k > 32 _batch_ * 64 _cpus_
+ * and __percpu_counter_compare() will still be fast. At that point hash map
+ * collisions will dominate its performance anyway. Assume that hash map filled
+ * to 50+% isn't going to be O(1) and use the following formula to choose
+ * between percpu_counter and atomic_t.
+ */
+#define PERCPU_COUNTER_BATCH 32
+	if (attr->max_entries / 2 > num_online_cpus() * PERCPU_COUNTER_BATCH)
+		htab->use_percpu_counter = true;
+
+	if (htab->use_percpu_counter) {
+		err = percpu_counter_init(&htab->pcount, 0, GFP_KERNEL);
+		if (err)
+			goto free_map_locked;
+	}
+
 	if (prealloc) {
 		err = prealloc_init(htab);
 		if (err)
@@ -576,6 +605,16 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 			if (err)
 				goto free_prealloc;
 		}
+	} else {
+		err = bpf_mem_alloc_init(&htab->ma, htab->elem_size, false);
+		if (err)
+			goto free_map_locked;
+		if (percpu) {
+			err = bpf_mem_alloc_init(&htab->pcpu_ma,
+						 round_up(htab->map.value_size, 8), true);
+			if (err)
+				goto free_map_locked;
+		}
 	}
 
 	return &htab->map;
@@ -586,6 +625,8 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
 		free_percpu(htab->map_locked[i]);
 	bpf_map_area_free(htab->buckets);
+	bpf_mem_alloc_destroy(&htab->pcpu_ma);
+	bpf_mem_alloc_destroy(&htab->ma);
 free_htab:
 	lockdep_unregister_key(&htab->lockdep_key);
 	bpf_map_area_free(htab);
@@ -860,17 +901,9 @@ static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
 static void htab_elem_free(struct bpf_htab *htab, struct htab_elem *l)
 {
 	if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH)
-		free_percpu(htab_elem_get_ptr(l, htab->map.key_size));
+		bpf_mem_cache_free(&htab->pcpu_ma, l->ptr_to_pptr);
 	check_and_free_fields(htab, l);
-	kfree(l);
-}
-
-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_elem_free(htab, l);
+	bpf_mem_cache_free(&htab->ma, l);
 }
 
 static void htab_put_fd_value(struct bpf_htab *htab, struct htab_elem *l)
@@ -884,6 +917,31 @@ static void htab_put_fd_value(struct bpf_htab *htab, struct htab_elem *l)
 	}
 }
 
+static bool is_map_full(struct bpf_htab *htab)
+{
+	if (htab->use_percpu_counter)
+		return __percpu_counter_compare(&htab->pcount, htab->map.max_entries,
+						PERCPU_COUNTER_BATCH) >= 0;
+	return atomic_read(&htab->count) >= htab->map.max_entries;
+}
+
+static void inc_elem_count(struct bpf_htab *htab)
+{
+	if (htab->use_percpu_counter)
+		percpu_counter_add_batch(&htab->pcount, 1, PERCPU_COUNTER_BATCH);
+	else
+		atomic_inc(&htab->count);
+}
+
+static void dec_elem_count(struct bpf_htab *htab)
+{
+	if (htab->use_percpu_counter)
+		percpu_counter_add_batch(&htab->pcount, -1, PERCPU_COUNTER_BATCH);
+	else
+		atomic_dec(&htab->count);
+}
+
+
 static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 {
 	htab_put_fd_value(htab, l);
@@ -892,9 +950,8 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
 		check_and_free_fields(htab, l);
 		__pcpu_freelist_push(&htab->freelist, &l->fnode);
 	} else {
-		atomic_dec(&htab->count);
-		l->htab = htab;
-		call_rcu(&l->rcu, htab_elem_free_rcu);
+		dec_elem_count(htab);
+		htab_elem_free(htab, l);
 	}
 }
 
@@ -919,13 +976,12 @@ static void pcpu_copy_value(struct bpf_htab *htab, void __percpu *pptr,
 static void pcpu_init_value(struct bpf_htab *htab, void __percpu *pptr,
 			    void *value, bool onallcpus)
 {
-	/* When using prealloc and not setting the initial value on all cpus,
-	 * zero-fill element values for other cpus (just as what happens when
-	 * not using prealloc). Otherwise, bpf program has no way to ensure
+	/* When not setting the initial value on all cpus, zero-fill element
+	 * values for other cpus. Otherwise, bpf program has no way to ensure
 	 * known initial values for cpus other than current one
 	 * (onallcpus=false always when coming from bpf prog).
 	 */
-	if (htab_is_prealloc(htab) && !onallcpus) {
+	if (!onallcpus) {
 		u32 size = round_up(htab->map.value_size, 8);
 		int current_cpu = raw_smp_processor_id();
 		int cpu;
@@ -976,19 +1032,16 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 			l_new = container_of(l, struct htab_elem, fnode);
 		}
 	} else {
-		if (atomic_inc_return(&htab->count) > htab->map.max_entries)
-			if (!old_elem) {
+		if (is_map_full(htab))
+			if (!old_elem)
 				/* when map is full and update() is replacing
 				 * old element, it's ok to allocate, since
 				 * old element will be freed immediately.
 				 * Otherwise return an error
 				 */
-				l_new = ERR_PTR(-E2BIG);
-				goto dec_count;
-			}
-		l_new = bpf_map_kmalloc_node(&htab->map, htab->elem_size,
-					     GFP_NOWAIT | __GFP_NOWARN,
-					     htab->map.numa_node);
+				return ERR_PTR(-E2BIG);
+		inc_elem_count(htab);
+		l_new = bpf_mem_cache_alloc(&htab->ma);
 		if (!l_new) {
 			l_new = ERR_PTR(-ENOMEM);
 			goto dec_count;
@@ -999,18 +1052,18 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 
 	memcpy(l_new->key, key, key_size);
 	if (percpu) {
-		size = round_up(size, 8);
 		if (prealloc) {
 			pptr = htab_elem_get_ptr(l_new, key_size);
 		} else {
 			/* alloc_percpu zero-fills */
-			pptr = bpf_map_alloc_percpu(&htab->map, size, 8,
-						    GFP_NOWAIT | __GFP_NOWARN);
+			pptr = bpf_mem_cache_alloc(&htab->pcpu_ma);
 			if (!pptr) {
-				kfree(l_new);
+				bpf_mem_cache_free(&htab->ma, l_new);
 				l_new = ERR_PTR(-ENOMEM);
 				goto dec_count;
 			}
+			l_new->ptr_to_pptr = pptr;
+			pptr = *(void **)pptr;
 		}
 
 		pcpu_init_value(htab, pptr, value, onallcpus);
@@ -1029,7 +1082,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 	l_new->hash = hash;
 	return l_new;
 dec_count:
-	atomic_dec(&htab->count);
+	dec_elem_count(htab);
 	return l_new;
 }
 
@@ -1429,6 +1482,10 @@ static void delete_all_elements(struct bpf_htab *htab)
 {
 	int i;
 
+	/* It's called from a worker thread, so disable migration here,
+	 * since bpf_mem_cache_free() relies on that.
+	 */
+	migrate_disable();
 	for (i = 0; i < htab->n_buckets; i++) {
 		struct hlist_nulls_head *head = select_bucket(htab, i);
 		struct hlist_nulls_node *n;
@@ -1439,6 +1496,7 @@ static void delete_all_elements(struct bpf_htab *htab)
 			htab_elem_free(htab, l);
 		}
 	}
+	migrate_enable();
 }
 
 static void htab_free_malloced_timers(struct bpf_htab *htab)
@@ -1488,10 +1546,10 @@ static void htab_map_free(struct bpf_map *map)
 	 * There is no need to synchronize_rcu() here to protect map elements.
 	 */
 
-	/* some of free_htab_elem() callbacks for elements of this map may
-	 * not have executed. Wait for them.
+	/* htab no longer uses call_rcu() directly. bpf_mem_alloc does it
+	 * underneath and is reponsible for waiting for callbacks to finish
+	 * during bpf_mem_alloc_destroy().
 	 */
-	rcu_barrier();
 	if (!htab_is_prealloc(htab)) {
 		delete_all_elements(htab);
 	} else {
@@ -1502,6 +1560,10 @@ static void htab_map_free(struct bpf_map *map)
 	bpf_map_free_kptr_off_tab(map);
 	free_percpu(htab->extra_elems);
 	bpf_map_area_free(htab->buckets);
+	bpf_mem_alloc_destroy(&htab->pcpu_ma);
+	bpf_mem_alloc_destroy(&htab->ma);
+	if (htab->use_percpu_counter)
+		percpu_counter_destroy(&htab->pcount);
 	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
 		free_percpu(htab->map_locked[i]);
 	lockdep_unregister_key(&htab->lockdep_key);

kernel/bpf/syscall.c

@@ -638,7 +638,10 @@ static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock)
 		bpf_map_free_id(map, do_idr_lock);
 		btf_put(map->btf);
 		INIT_WORK(&map->work, bpf_map_free_deferred);
-		schedule_work(&map->work);
+		/* Avoid spawning kworkers, since they all might contend
+		 * for the same mutex like slab_mutex.
+		 */
+		queue_work(system_unbound_wq, &map->work);
 	}
 }
 

kernel/bpf/verifier.c

@@ -12586,14 +12586,6 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
 	return err;
 }
 
-static int check_map_prealloc(struct bpf_map *map)
-{
-	return (map->map_type != BPF_MAP_TYPE_HASH &&
-		map->map_type != BPF_MAP_TYPE_PERCPU_HASH &&
-		map->map_type != BPF_MAP_TYPE_HASH_OF_MAPS) ||
-		!(map->map_flags & BPF_F_NO_PREALLOC);
-}
-
 static bool is_tracing_prog_type(enum bpf_prog_type type)
 {
 	switch (type) {
@@ -12608,50 +12600,12 @@ static bool is_tracing_prog_type(enum bpf_prog_type type)
 	}
 }
 
-static bool is_preallocated_map(struct bpf_map *map)
-{
-	if (!check_map_prealloc(map))
-		return false;
-	if (map->inner_map_meta && !check_map_prealloc(map->inner_map_meta))
-		return false;
-	return true;
-}
-
 static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 					struct bpf_map *map,
 					struct bpf_prog *prog)
 
 {
 	enum bpf_prog_type prog_type = resolve_prog_type(prog);
-	/*
-	 * Validate that trace type programs use preallocated hash maps.
-	 *
-	 * For programs attached to PERF events this is mandatory as the
-	 * perf NMI can hit any arbitrary code sequence.
-	 *
-	 * All other trace types using preallocated hash maps are unsafe as
-	 * well because tracepoint or kprobes can be inside locked regions
-	 * of the memory allocator or at a place where a recursion into the
-	 * memory allocator would see inconsistent state.
-	 *
-	 * On RT enabled kernels run-time allocation of all trace type
-	 * programs is strictly prohibited due to lock type constraints. On
-	 * !RT kernels it is allowed for backwards compatibility reasons for
-	 * now, but warnings are emitted so developers are made aware of
-	 * the unsafety and can fix their programs before this is enforced.
-	 */
-	if (is_tracing_prog_type(prog_type) && !is_preallocated_map(map)) {
-		if (prog_type == BPF_PROG_TYPE_PERF_EVENT) {
-			verbose(env, "perf_event programs can only use preallocated hash map\n");
-			return -EINVAL;
-		}
-		if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
-			verbose(env, "trace type programs can only use preallocated hash map\n");
-			return -EINVAL;
-		}
-		WARN_ONCE(1, "trace type BPF program uses run-time allocation\n");
-		verbose(env, "trace type programs with run-time allocated hash maps are unsafe. Switch to preallocated hash maps.\n");
-	}
 
 	if (map_value_has_spin_lock(map)) {
 		if (prog_type == BPF_PROG_TYPE_SOCKET_FILTER) {
@@ -12698,12 +12652,6 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 		case BPF_MAP_TYPE_LRU_PERCPU_HASH:
 		case BPF_MAP_TYPE_ARRAY_OF_MAPS:
 		case BPF_MAP_TYPE_HASH_OF_MAPS:
-			if (!is_preallocated_map(map)) {
-				verbose(env,
-					"Sleepable programs can only use preallocated maps\n");
-				return -EINVAL;
-			}
-			break;
 		case BPF_MAP_TYPE_RINGBUF:
 		case BPF_MAP_TYPE_INODE_STORAGE:
 		case BPF_MAP_TYPE_SK_STORAGE:

samples/bpf/map_perf_test_kern.c

@@ -108,11 +108,14 @@ int stress_hmap(struct pt_regs *ctx)
 	u32 key = bpf_get_current_pid_tgid();
 	long init_val = 1;
 	long *value;
+	int i;
 
+	for (i = 0; i < 10; i++) {
 		bpf_map_update_elem(&hash_map, &key, &init_val, BPF_ANY);
 		value = bpf_map_lookup_elem(&hash_map, &key);
 		if (value)
 			bpf_map_delete_elem(&hash_map, &key);
+	}
 
 	return 0;
 }
@@ -123,11 +126,14 @@ int stress_percpu_hmap(struct pt_regs *ctx)
 	u32 key = bpf_get_current_pid_tgid();
 	long init_val = 1;
 	long *value;
+	int i;
 
+	for (i = 0; i < 10; i++) {
 		bpf_map_update_elem(&percpu_hash_map, &key, &init_val, BPF_ANY);
 		value = bpf_map_lookup_elem(&percpu_hash_map, &key);
 		if (value)
 			bpf_map_delete_elem(&percpu_hash_map, &key);
+	}
 	return 0;
 }
 
@@ -137,11 +143,14 @@ int stress_hmap_alloc(struct pt_regs *ctx)
 	u32 key = bpf_get_current_pid_tgid();
 	long init_val = 1;
 	long *value;
+	int i;
 
+	for (i = 0; i < 10; i++) {
 		bpf_map_update_elem(&hash_map_alloc, &key, &init_val, BPF_ANY);
 		value = bpf_map_lookup_elem(&hash_map_alloc, &key);
 		if (value)
 			bpf_map_delete_elem(&hash_map_alloc, &key);
+	}
 	return 0;
 }
 
@@ -151,11 +160,14 @@ int stress_percpu_hmap_alloc(struct pt_regs *ctx)
 	u32 key = bpf_get_current_pid_tgid();
 	long init_val = 1;
 	long *value;
+	int i;
 
+	for (i = 0; i < 10; i++) {
 		bpf_map_update_elem(&percpu_hash_map_alloc, &key, &init_val, BPF_ANY);
 		value = bpf_map_lookup_elem(&percpu_hash_map_alloc, &key);
 		if (value)
 			bpf_map_delete_elem(&percpu_hash_map_alloc, &key);
+	}
 	return 0;
 }
 

samples/bpf/map_perf_test_user.c

@@ -72,7 +72,7 @@ static int test_flags = ~0;
 static uint32_t num_map_entries;
 static uint32_t inner_lru_hash_size;
 static int lru_hash_lookup_test_entries = 32;
-static uint32_t max_cnt = 1000000;
+static uint32_t max_cnt = 10000;
 
 static int check_test_flags(enum test_type t)
 {

tools/testing/selftests/bpf/progs/timer.c

@@ -208,17 +208,6 @@ static int timer_cb2(void *map, int *key, struct hmap_elem *val)
 		 */
 		bpf_map_delete_elem(map, key);
 
-		/* in non-preallocated hashmap both 'key' and 'val' are RCU
-		 * protected and still valid though this element was deleted
-		 * from the map. Arm this timer for ~35 seconds. When callback
-		 * finishes the call_rcu will invoke:
-		 * htab_elem_free_rcu
-		 *   check_and_free_timer
-		 *     bpf_timer_cancel_and_free
-		 * to cancel this 35 second sleep and delete the timer for real.
-		 */
-		if (bpf_timer_start(&val->timer, 1ull << 35, 0) != 0)
-			err |= 256;
 		ok |= 4;
 	}
 	return 0;

tools/testing/selftests/bpf/test_maps.c

@@ -264,10 +264,11 @@ static void test_hashmap_percpu(unsigned int task, void *data)
 	close(fd);
 }
 
+#define VALUE_SIZE 3
 static int helper_fill_hashmap(int max_entries)
 {
 	int i, fd, ret;
-	long long key, value;
+	long long key, value[VALUE_SIZE] = {};
 
 	fd = bpf_map_create(BPF_MAP_TYPE_HASH, NULL, sizeof(key), sizeof(value),
 			    max_entries, &map_opts);
@@ -276,8 +277,8 @@ static int helper_fill_hashmap(int max_entries)
 	      "err: %s, flags: 0x%x\n", strerror(errno), map_opts.map_flags);
 
 	for (i = 0; i < max_entries; i++) {
-		key = i; value = key;
-		ret = bpf_map_update_elem(fd, &key, &value, BPF_NOEXIST);
+		key = i; value[0] = key;
+		ret = bpf_map_update_elem(fd, &key, value, BPF_NOEXIST);
 		CHECK(ret != 0,
 		      "can't update hashmap",
 		      "err: %s\n", strerror(ret));
@@ -288,8 +289,8 @@ static int helper_fill_hashmap(int max_entries)
 
 static void test_hashmap_walk(unsigned int task, void *data)
 {
-	int fd, i, max_entries = 1000;
-	long long key, value, next_key;
+	int fd, i, max_entries = 10000;
+	long long key, value[VALUE_SIZE], next_key;
 	bool next_key_valid = true;
 
 	fd = helper_fill_hashmap(max_entries);
@@ -297,7 +298,7 @@ static void test_hashmap_walk(unsigned int task, void *data)
 	for (i = 0; bpf_map_get_next_key(fd, !i ? NULL : &key,
 					 &next_key) == 0; i++) {
 		key = next_key;
-		assert(bpf_map_lookup_elem(fd, &key, &value) == 0);
+		assert(bpf_map_lookup_elem(fd, &key, value) == 0);
 	}
 
 	assert(i == max_entries);
@@ -305,9 +306,9 @@ static void test_hashmap_walk(unsigned int task, void *data)
 	assert(bpf_map_get_next_key(fd, NULL, &key) == 0);
 	for (i = 0; next_key_valid; i++) {
 		next_key_valid = bpf_map_get_next_key(fd, &key, &next_key) == 0;
-		assert(bpf_map_lookup_elem(fd, &key, &value) == 0);
-		value++;
-		assert(bpf_map_update_elem(fd, &key, &value, BPF_EXIST) == 0);
+		assert(bpf_map_lookup_elem(fd, &key, value) == 0);
+		value[0]++;
+		assert(bpf_map_update_elem(fd, &key, value, BPF_EXIST) == 0);
 		key = next_key;
 	}
 
@@ -316,8 +317,8 @@ static void test_hashmap_walk(unsigned int task, void *data)
 	for (i = 0; bpf_map_get_next_key(fd, !i ? NULL : &key,
 					 &next_key) == 0; i++) {
 		key = next_key;
-		assert(bpf_map_lookup_elem(fd, &key, &value) == 0);
-		assert(value - 1 == key);
+		assert(bpf_map_lookup_elem(fd, &key, value) == 0);
+		assert(value[0] - 1 == key);
 	}
 
 	assert(i == max_entries);
@@ -1371,16 +1372,16 @@ static void __run_parallel(unsigned int tasks,
 
 static void test_map_stress(void)
 {
+	run_parallel(100, test_hashmap_walk, NULL);
 	run_parallel(100, test_hashmap, NULL);
 	run_parallel(100, test_hashmap_percpu, NULL);
 	run_parallel(100, test_hashmap_sizes, NULL);
-	run_parallel(100, test_hashmap_walk, NULL);
 
 	run_parallel(100, test_arraymap, NULL);
 	run_parallel(100, test_arraymap_percpu, NULL);
 }
 
-#define TASKS 1024
+#define TASKS 100
 
 #define DO_UPDATE 1
 #define DO_DELETE 0
@@ -1432,6 +1433,8 @@ static void test_update_delete(unsigned int fn, void *data)
 	int fd = ((int *)data)[0];
 	int i, key, value, err;
 
+	if (fn & 1)
+		test_hashmap_walk(fn, NULL);
 	for (i = fn; i < MAP_SIZE; i += TASKS) {
 		key = value = i;
 
@@ -1455,7 +1458,7 @@ static void test_update_delete(unsigned int fn, void *data)
 
 static void test_map_parallel(void)
 {
-	int i, fd, key = 0, value = 0;
+	int i, fd, key = 0, value = 0, j = 0;
 	int data[2];
 
 	fd = bpf_map_create(BPF_MAP_TYPE_HASH, NULL, sizeof(key), sizeof(value),
@@ -1466,6 +1469,7 @@ static void test_map_parallel(void)
 		exit(1);
 	}
 
+again:
 	/* Use the same fd in children to add elements to this map:
 	 * child_0 adds key=0, key=1024, key=2048, ...
 	 * child_1 adds key=1, key=1025, key=2049, ...
@@ -1502,6 +1506,12 @@ static void test_map_parallel(void)
 	key = -1;
 	assert(bpf_map_get_next_key(fd, NULL, &key) < 0 && errno == ENOENT);
 	assert(bpf_map_get_next_key(fd, &key, &key) < 0 && errno == ENOENT);
+
+	key = 0;
+	bpf_map_delete_elem(fd, &key);
+	if (j++ < 5)
+		goto again;
+	close(fd);
 }
 
 static void test_map_rdonly(void)