[v2,bpf-next] bpf: Fix build without BPF_SYSCALL, but with BPF_JIT.

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’

This is due to:
obj-$(CONFIG_BPF_JIT) += trampoline.o
obj-$(CONFIG_BPF_JIT) += dispatcher.o
There is a number of functions that arch/x86/net/bpf_jit_comp.c is
using from these two files, but none of them will be used when
only cBPF is on (which is the case for BPF_SYSCALL=n BPF_JIT=y).

Add rcu_trace functions to rcupdate_trace.h. The JITed code won't execute 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")
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/rcupdate_trace.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

On Mon, Aug 31, 2020 at 08:51:55AM -0700, Alexei Starovoitov wrote:
> 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’
> 
> This is due to:
> obj-$(CONFIG_BPF_JIT) += trampoline.o
> obj-$(CONFIG_BPF_JIT) += dispatcher.o
> There is a number of functions that arch/x86/net/bpf_jit_comp.c is
> using from these two files, but none of them will be used when
> only cBPF is on (which is the case for BPF_SYSCALL=n BPF_JIT=y).
> 
> Add rcu_trace functions to rcupdate_trace.h. The JITed code won't execute 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")
> Acked-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Looks good, and unless someone tells me otherwise, I am assuming that
this one goes up the normal BPF patch route.

							Thanx, Paul

> ---
>  include/linux/rcupdate_trace.h | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h
> index d9015aac78c6..aaaac8ac927c 100644
> --- a/include/linux/rcupdate_trace.h
> +++ b/include/linux/rcupdate_trace.h
> @@ -82,7 +82,14 @@ 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
> +/*
> + * The BPF JIT forms these addresses even when it doesn't call these
> + * functions, so provide definitions that result in runtime errors.
> + */
> +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
>

On 8/31/20 5:51 PM, Alexei Starovoitov wrote:
> 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’
> 
> This is due to:
> obj-$(CONFIG_BPF_JIT) += trampoline.o
> obj-$(CONFIG_BPF_JIT) += dispatcher.o
> There is a number of functions that arch/x86/net/bpf_jit_comp.c is
> using from these two files, but none of them will be used when
> only cBPF is on (which is the case for BPF_SYSCALL=n BPF_JIT=y).
> 
> Add rcu_trace functions to rcupdate_trace.h. The JITed code won't execute 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")
> Acked-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Applied, thanks!