Right now we are not using rcu api correctly: we pass __rcu pointers to bpf_prog_array_xyz routines but don't use rcu_dereference on them (see bpf_prog_array_delete_safe and bpf_prog_array_copy in particular). Instead of sprinkling rcu_dereferences, let's just get rid of those __rcu annotations and move rcu handling to a higher level. It looks like all those routines are called from the rcu update side and we can use simple rcu_dereference_protected to get a reference that is valid as long as we hold a mutex (i.e. no other updater can change the pointer, no need for rcu read section and there should not be a use-after-free problem). To be fair, there is currently no issue with the existing approach since the calls are mutex-protected, pointer values don't change, __rcu annotations are ignored. But it's still nice to use proper api. The series fixes the following sparse warnings: kernel/bpf/core.c:1876:44: warning: incorrect type in initializer (different address spaces) kernel/bpf/core.c:1876:44: expected struct bpf_prog_array_item *item kernel/bpf/core.c:1876:44: got struct bpf_prog_array_item [noderef] <asn:4> * kernel/bpf/core.c:1900:26: warning: incorrect type in assignment (different address spaces) kernel/bpf/core.c:1900:26: expected struct bpf_prog_array_item *existing kernel/bpf/core.c:1900:26: got struct bpf_prog_array_item [noderef] <asn:4> * kernel/bpf/core.c:1934:26: warning: incorrect type in assignment (different address spaces) kernel/bpf/core.c:1934:26: expected struct bpf_prog_array_item *[assigned] existing kernel/bpf/core.c:1934:26: got struct bpf_prog_array_item [noderef] <asn:4> * Stanislav Fomichev (4): bpf: remove __rcu annotations from bpf_prog_array bpf: media: properly use bpf_prog_array api bpf: cgroup: properly use bpf_prog_array api bpf: tracing: properly use bpf_prog_array api drivers/media/rc/bpf-lirc.c | 27 +++++++++++++++++---------- include/linux/bpf-cgroup.h | 2 +- include/linux/bpf.h | 12 ++++++------ kernel/bpf/cgroup.c | 27 +++++++++++++++++---------- kernel/bpf/core.c | 31 ++++++++++++------------------- kernel/trace/bpf_trace.c | 18 ++++++++++-------- 6 files changed, 63 insertions(+), 54 deletions(-) -- 2.21.0.1020.gf2820cf01a-goog
