On Sun, Aug 30, 2020 at 01:43:28PM -0700, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> 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@xxxxxxxxx>
> Fixes: 1e6c62a88215 ("bpf: Introduce sleepable BPF programs")
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
A couple of nits below, but overall:
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
> 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
This formulation is a bit novel for RCU. Could we therefore please add
a comment something like this?
// 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();
> +}
People have been moving towards one-liner for things like these last two:
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
>
