On 1/8/21 2:09 PM, Andrii Nakryiko wrote:
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_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@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
