[PATCH bpf-next] bpf: Fix build without BPF_SYSCALL, but with BPF_JIT.

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

From: Alexei Starovoitov <ast@kernel.org>

When CONFIG_BPF_SYSCALL is not set, but CONFIG_BPF_JIT=y
the kernel build fails:
In file included from ../kernel/bpf/trampoline.c:11:
../kernel/bpf/trampoline.c: In function ‘bpf_trampoline_update’:
../kernel/bpf/trampoline.c:220:39: error: ‘call_rcu_tasks_trace’ undeclared
../kernel/bpf/trampoline.c: In function ‘__bpf_prog_enter_sleepable’:
../kernel/bpf/trampoline.c:411:2: error: implicit declaration of function ‘rcu_read_lock_trace’
../kernel/bpf/trampoline.c: In function ‘__bpf_prog_exit_sleepable’:
../kernel/bpf/trampoline.c:416:2: error: implicit declaration of function ‘rcu_read_unlock_trace’

Add these functions to rcupdate_trace.h.
The JIT won't call them and BPF trampoline logic won't be used without BPF_SYSCALL.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 1e6c62a88215 ("bpf: Introduce sleepable BPF programs")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/rcupdate_trace.h | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h
index d9015aac78c6..334840f4f245 100644
--- a/include/linux/rcupdate_trace.h
+++ b/include/linux/rcupdate_trace.h
@@ -82,7 +82,19 @@ static inline void rcu_read_unlock_trace(void)
 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
 void synchronize_rcu_tasks_trace(void);
 void rcu_barrier_tasks_trace(void);
-
+#else
+static inline void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func)
+{
+	BUG();
+}
+static inline void rcu_read_lock_trace(void)
+{
+	BUG();
+}
+static inline void rcu_read_unlock_trace(void)
+{
+	BUG();
+}
 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
 
 #endif /* __LINUX_RCUPDATE_TRACE_H */
-- 
2.23.0