On 1/31/23 1:00 PM, Dave Marchevsky wrote:
> This patch eliminates extra bpf_reg_state memory usage added due to
> previous patch keeping a copy of lock identity in reg state for
> non-owning refs.
>
> Instead of copying lock identity around, this patch changes
> non_owning_ref_lock field to be a bool, taking advantage of the
> following:
>
> * There can currently only be one active lock at a time
> * non-owning refs are only valid in the critical section
>
> So if a verifier_state has an active_lock, any non-owning ref must've
> been obtained under that lock, and any non-owning ref not obtained under
> that lock must have been invalidated previously. Therefore if a
> non-owning ref is associated with a lock, it's the active_lock of the
> current state. So we can keep a bool "are we associated with active_lock
> of current state" instead of copying lock identity around.
>
> Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
> ---
> include/linux/bpf_verifier.h | 2 +-
> kernel/bpf/verifier.c | 20 ++++++++++----------
> 2 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 1c6bbde40705..baeb5afb0b81 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -84,7 +84,7 @@ struct bpf_reg_state {
> struct {
> struct btf *btf;
> u32 btf_id;
> - struct bpf_active_lock non_owning_ref_lock;
> + bool non_owning_ref_lock;
> };
>
> u32 mem_size; /* for PTR_TO_MEM | PTR_TO_MEM_OR_NULL */
Pahole output after this change:
union {
int range; /* 8 4 */
struct {
struct bpf_map * map_ptr; /* 8 8 */
u32 map_uid; /* 16 4 */
}; /* 8 16 */
struct {
struct btf * btf; /* 8 8 */
u32 btf_id; /* 16 4 */
bool non_owning_ref_lock; /* 20 1 */
}; /* 8 16 */
u32 mem_size; /* 8 4 */
struct {
enum bpf_dynptr_type type; /* 8 4 */
bool first_slot; /* 12 1 */
} dynptr; /* 8 8 */
struct {
long unsigned int raw1; /* 8 8 */
long unsigned int raw2; /* 16 8 */
} raw; /* 8 16 */
u32 subprogno; /* 8 4 */
}; /* 8 16 */
The PTR_TO_BTF_ID union entry was taking 24 bytes in previous commit,
now it's down to 16, so back to same size as before previous commit.
