mainline inclusion
from mainline-5.12-rc1
commit 635599ba
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=635599bace259a2c42741c3ea61bfa7be6f15556

-------------------------------------------------

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: 9f7fa225 ("selftests/bpf: Add bpf_testmod kernel module for testing")
Suggested-by: NAlexei Starovoitov <ast@kernel.org>
Signed-off-by: NAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NYonghong Song <yhs@fb.com>
Acked-by: NHao Luo <haoluo@google.com>
Link: https://lore.kernel.org/bpf/20210112075520.4103414-5-andrii@kernel.org
(cherry picked from commit 635599ba)
Signed-off-by: NWang Yufen <wangyufen@huawei.com>