diff options
| author | Matt Bobrowski <mattbobrowski@google.com> | 2026-01-21 09:00:01 +0000 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-01-21 09:38:16 -0800 |
| commit | d0f5d4f8f3285349bfb94fa84555ab267d2c041d (patch) | |
| tree | b02e9f2dee5dce799a1150ce4b1ad8aee85b2571 | |
| parent | ca674a032fb3ecc8e658ba24dd40b8c3dfff4dff (diff) | |
bpf: Revert "bpf: drop KF_ACQUIRE flag on BPF kfunc bpf_get_root_mem_cgroup()"
This reverts commit e463b6de9da1 ("bpf: drop KF_ACQUIRE flag on BPF
kfunc bpf_get_root_mem_cgroup()").
The original commit removed the KF_ACQUIRE flag from
bpf_get_root_mem_cgroup() under the assumption that it resulted in
simplified usage. This stemmed from the fact that
bpf_get_root_mem_cgroup() inherently returns a reference to an object
which technically isn't reference counted, therefore there is no
strong requirement to call a matching bpf_put_mem_cgroup() on the
returned reference.
Although technically correct, as per the arguments in the thread [0],
dropping the KF_ACQUIRE flag and losing reference tracking semantics
negatively impacted the usability of bpf_get_root_mem_cgroup() in
practice.
[0] https://lore.kernel.org/bpf/878qdx6yut.fsf@linux.dev/
Link: https://lore.kernel.org/bpf/CAADnVQ+6d1Lj4dteAv8u62d7kj3Ze5io6bqM0xeQd-UPk9ZgJQ@mail.gmail.com/
Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
Link: https://lore.kernel.org/r/20260121090001.240166-1-mattbobrowski@google.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
| -rw-r--r-- | mm/bpf_memcontrol.c | 14 |
1 files changed, 7 insertions, 7 deletions
diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c index f95cd5d16f4c..716df49d7647 100644 --- a/mm/bpf_memcontrol.c +++ b/mm/bpf_memcontrol.c @@ -13,12 +13,12 @@ __bpf_kfunc_start_defs(); /** * bpf_get_root_mem_cgroup - Returns a pointer to the root memory cgroup * - * Return: A pointer to the root memory cgroup. Notably, the pointer to the - * returned struct mem_cgroup is trusted by default, so it's perfectably - * acceptable to also pass this pointer into other BPF kfuncs (e.g., - * bpf_mem_cgroup_usage()). Additionally, this BPF kfunc does not make use of - * KF_ACQUIRE semantics, so there's no requirement for the BPF program to call - * bpf_put_mem_cgroup() on the pointer returned by this BPF kfunc. + * The function has KF_ACQUIRE semantics, even though the root memory + * cgroup is never destroyed after being created and doesn't require + * reference counting. And it's perfectly safe to pass it to + * bpf_put_mem_cgroup() + * + * Return: A pointer to the root memory cgroup. */ __bpf_kfunc struct mem_cgroup *bpf_get_root_mem_cgroup(void) { @@ -162,7 +162,7 @@ __bpf_kfunc void bpf_mem_cgroup_flush_stats(struct mem_cgroup *memcg) __bpf_kfunc_end_defs(); BTF_KFUNCS_START(bpf_memcontrol_kfuncs) -BTF_ID_FLAGS(func, bpf_get_root_mem_cgroup, KF_RET_NULL) +BTF_ID_FLAGS(func, bpf_get_root_mem_cgroup, KF_ACQUIRE | KF_RET_NULL) BTF_ID_FLAGS(func, bpf_get_mem_cgroup, KF_ACQUIRE | KF_RET_NULL | KF_RCU) BTF_ID_FLAGS(func, bpf_put_mem_cgroup, KF_RELEASE) |