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bpf: introduce BPF_F_LOCK flag

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Introduce BPF_F_LOCK flag for map_lookup and map_update syscall commands
and for map_update() helper function.
In all these cases take a lock of existing element (which was provided
in BTF description) before copying (in or out) the rest of map value.

Implementation details that are part of uapi:

Array:
The array map takes the element lock for lookup/update.

Hash:
hash map also takes the lock for lookup/update and tries to avoid the bucket lock.
If old element exists it takes the element lock and updates the element in place.
If element doesn't exist it allocates new one and inserts into hash table
while holding the bucket lock.
In rare case the hashmap has to take both the bucket lock and the element lock
to update old value in place.

Cgroup local storage:
It is similar to array. update in place and lookup are done with lock taken.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Alexei Starovoitov
2019-01-31 15:40:09 -08:00
committed by Daniel Borkmann
parent ab963beb9f
commit 96049f3afd
7 changed files with 110 additions and 14 deletions
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24
kernel/bpf/arraymap.c
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@@ -253,8 +253,9 @@ static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
u32 index = *(u32 *)key;
char *val;
if (unlikely(map_flags > BPF_EXIST))
if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST))
/* unknown flags */
return -EINVAL;
@@ -262,18 +263,25 @@ static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
/* all elements were pre-allocated, cannot insert a new one */
return -E2BIG;
if (unlikely(map_flags == BPF_NOEXIST))
if (unlikely(map_flags & BPF_NOEXIST))
/* all elements already exist */
return -EEXIST;
if (array->map.map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
if (unlikely((map_flags & BPF_F_LOCK) &&
!map_value_has_spin_lock(map)))
return -EINVAL;
if (array->map.map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
memcpy(this_cpu_ptr(array->pptrs[index & array->index_mask]),
value, map->value_size);
else
copy_map_value(map,
array->value +
array->elem_size * (index & array->index_mask),
value);
} else {
val = array->value +
array->elem_size * (index & array->index_mask);
if (map_flags & BPF_F_LOCK)
copy_map_value_locked(map, val, value, false);
else
copy_map_value(map, val, value);
}
return 0;
}