diff options
| author | Kui-Feng Lee <kuifeng@meta.com> | 2023-03-22 20:23:58 -0700 |
|---|---|---|
| committer | Martin KaFai Lau <martin.lau@kernel.org> | 2023-03-22 22:51:47 -0700 |
| commit | b671c2067a04c0668df174ff5dfdb573d1f9b074 (patch) | |
| tree | 81b83fbcca8f6749dafec7c851bdee4ced3c8619 /kernel/bpf/syscall.c | |
| parent | b63cbc490e18d893632929b8faa55bb28da3fcd4 (diff) | |
bpf: Retire the struct_ops map kvalue->refcnt.
We have replaced kvalue-refcnt with synchronize_rcu() to wait for an
RCU grace period.
Maintenance of kvalue->refcnt was a complicated task, as we had to
simultaneously keep track of two reference counts: one for the
reference count of bpf_map. When the kvalue->refcnt reaches zero, we
also have to reduce the reference count on bpf_map - yet these steps
are not performed in an atomic manner and require us to be vigilant
when managing them. By eliminating kvalue->refcnt, we can make our
maintenance more straightforward as the refcount of bpf_map is now
solely managed!
To prevent the trampoline image of a struct_ops from being released
while it is still in use, we wait for an RCU grace period. The
setsockopt(TCP_CONGESTION, "...") command allows you to change your
socket's congestion control algorithm and can result in releasing the
old struct_ops implementation. It is fine. However, this function is
exposed through bpf_setsockopt(), it may be accessed by BPF programs
as well. To ensure that the trampoline image belonging to struct_op
can be safely called while its method is in use, the trampoline
safeguarde the BPF program with rcu_read_lock(). Doing so prevents any
destruction of the associated images before returning from a
trampoline and requires us to wait for an RCU grace period.
Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
Link: https://lore.kernel.org/r/20230323032405.3735486-2-kuifeng@meta.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Diffstat (limited to 'kernel/bpf/syscall.c')
| -rw-r--r-- | kernel/bpf/syscall.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 099e9068bcdd..cff0348a2871 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1303,8 +1303,10 @@ struct bpf_map *bpf_map_get_with_uref(u32 ufd) return map; } -/* map_idr_lock should have been held */ -static struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref) +/* map_idr_lock should have been held or the map should have been + * protected by rcu read lock. + */ +struct bpf_map *__bpf_map_inc_not_zero(struct bpf_map *map, bool uref) { int refold; |