netdev - Re: [PATCH v2 bpf-next] bpf: Fix build without BPF_SYSCALL, but with BPF

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Date:   Mon, 31 Aug 2020 09:19:49 -0700
From:   Alexei Starovoitov <ast@...com>
To:     <paulmck@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     <davem@...emloft.net>, <daniel@...earbox.net>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next] bpf: Fix build without BPF_SYSCALL, but with
 BPF_JIT.

On 8/31/20 9:15 AM, Paul E. McKenney wrote:
> On Mon, Aug 31, 2020 at 08:51:55AM -0700, Alexei Starovoitov wrote:
>> From: Alexei Starovoitov <ast@...nel.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@...el.com>
>> Fixes: 1e6c62a88215 ("bpf: Introduce sleepable BPF programs")
>> Acked-by: Paul E. McKenney <paulmck@...nel.org>
>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> 
> Looks good, and unless someone tells me otherwise, I am assuming that
> this one goes up the normal BPF patch route.

Yes. It fixes the issue in bpf-next tree.