selftests/bpf: Sync RCU before unloading bpf_testmod
authorAndrii Nakryiko <andrii@kernel.org>
Tue, 12 Jan 2021 07:55:17 +0000 (23:55 -0800)
committerAlexei Starovoitov <ast@kernel.org>
Wed, 13 Jan 2021 01:23:47 +0000 (17:23 -0800)
commit635599bace259a2c42741c3ea61bfa7be6f15556
treea50085d6b0dc9ca61778aad8a06cc285114c3084
parent936f8946bdb48239f4292812d4d2e26c6d328c95
selftests/bpf: Sync RCU before unloading bpf_testmod

If some of the subtests use module BTFs through ksyms, they will cause
bpf_prog to take a refcount on bpf_testmod module, which will prevent it from
successfully unloading. Module's refcnt is decremented when bpf_prog is freed,
which generally happens in RCU callback. So we need to trigger
syncronize_rcu() in the kernel, which can be achieved nicely with
membarrier(MEMBARRIER_CMD_SHARED) or membarrier(MEMBARRIER_CMD_GLOBAL) syscall.
So do that in kernel_sync_rcu() and make it available to other test inside the
test_progs. This synchronize_rcu() is called before attempting to unload
bpf_testmod.

Fixes: 9f7fa225894c ("selftests/bpf: Add bpf_testmod kernel module for testing")
Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Hao Luo <haoluo@google.com>
Link: https://lore.kernel.org/bpf/20210112075520.4103414-5-andrii@kernel.org
tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c
tools/testing/selftests/bpf/test_progs.c
tools/testing/selftests/bpf/test_progs.h