Re: [PATCH net-next 3/3] bpf: avoid stack copy and use skb ctx for event output

[kbuild test robot]

Hi,

[auto build test WARNING on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Daniel-Borkmann/BPF-event-output-helper-improvements/20160713-065944
config: s390-allyesconfig (attached as .config)
compiler: s390x-linux-gnu-gcc (Debian 5.3.1-8) 5.3.1 20160205
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=s390 

All warnings (new ones prefixed by >>):

   kernel/trace/bpf_trace.c: In function 'bpf_perf_event_output':
   kernel/trace/bpf_trace.c:284:1: warning: 'bpf_perf_event_output' uses dynamic stack allocation
    }
    ^
   kernel/trace/bpf_trace.c: In function 'bpf_event_output':
>> kernel/trace/bpf_trace.c:319:1: warning: 'bpf_event_output' uses dynamic stack allocation
    }
    ^

vim +/bpf_event_output +319 kernel/trace/bpf_trace.c

3644f5a9 Daniel Borkmann    2016-07-13  278  	if (unlikely(flags & ~(BPF_F_INDEX_MASK)))
3644f5a9 Daniel Borkmann    2016-07-13  279  		return -EINVAL;
3644f5a9 Daniel Borkmann    2016-07-13  280  
3644f5a9 Daniel Borkmann    2016-07-13  281  	return __bpf_perf_event_output((struct pt_regs *)(long) r1,
3644f5a9 Daniel Borkmann    2016-07-13  282  				       (struct bpf_map *)(long) r2,
3644f5a9 Daniel Borkmann    2016-07-13  283  				       flags, &raw);
3644f5a9 Daniel Borkmann    2016-07-13 @284  }
3644f5a9 Daniel Borkmann    2016-07-13  285  
a43eec30 Alexei Starovoitov 2015-10-20  286  static const struct bpf_func_proto bpf_perf_event_output_proto = {
a43eec30 Alexei Starovoitov 2015-10-20  287  	.func		= bpf_perf_event_output,
1075ef59 Alexei Starovoitov 2015-10-23  288  	.gpl_only	= true,
a43eec30 Alexei Starovoitov 2015-10-20  289  	.ret_type	= RET_INTEGER,
a43eec30 Alexei Starovoitov 2015-10-20  290  	.arg1_type	= ARG_PTR_TO_CTX,
a43eec30 Alexei Starovoitov 2015-10-20  291  	.arg2_type	= ARG_CONST_MAP_PTR,
a43eec30 Alexei Starovoitov 2015-10-20  292  	.arg3_type	= ARG_ANYTHING,
a43eec30 Alexei Starovoitov 2015-10-20  293  	.arg4_type	= ARG_PTR_TO_STACK,
a43eec30 Alexei Starovoitov 2015-10-20  294  	.arg5_type	= ARG_CONST_STACK_SIZE,
a43eec30 Alexei Starovoitov 2015-10-20  295  };
a43eec30 Alexei Starovoitov 2015-10-20  296  
bd570ff9 Daniel Borkmann    2016-04-18  297  static DEFINE_PER_CPU(struct pt_regs, bpf_pt_regs);
bd570ff9 Daniel Borkmann    2016-04-18  298  
f428cc22 Daniel Borkmann    2016-07-13  299  u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 size_meta,
f428cc22 Daniel Borkmann    2016-07-13  300  		     void *ctx, u64 size_ctx,
f428cc22 Daniel Borkmann    2016-07-13  301  		     unsigned long (*ctx_copy_cb)(void *dst, const void *src,
f428cc22 Daniel Borkmann    2016-07-13  302  						  unsigned long n))
bd570ff9 Daniel Borkmann    2016-04-18  303  {
bd570ff9 Daniel Borkmann    2016-04-18  304  	struct pt_regs *regs = this_cpu_ptr(&bpf_pt_regs);
f428cc22 Daniel Borkmann    2016-07-13  305  	struct perf_raw_record_frag frag = {
f428cc22 Daniel Borkmann    2016-07-13  306  		.data		= ctx,
f428cc22 Daniel Borkmann    2016-07-13  307  		.copy_cb	= ctx_copy_cb,
f428cc22 Daniel Borkmann    2016-07-13  308  	};
f428cc22 Daniel Borkmann    2016-07-13  309  	struct perf_raw_record raw = {
f428cc22 Daniel Borkmann    2016-07-13  310  		.size		= size_meta + size_ctx,
f428cc22 Daniel Borkmann    2016-07-13  311  		.size_head	= size_meta,
f428cc22 Daniel Borkmann    2016-07-13  312  		.data		= meta,
f428cc22 Daniel Borkmann    2016-07-13  313  		.frag		= size_ctx ? &frag : NULL,
f428cc22 Daniel Borkmann    2016-07-13  314  	};
bd570ff9 Daniel Borkmann    2016-04-18  315  
bd570ff9 Daniel Borkmann    2016-04-18  316  	perf_fetch_caller_regs(regs);
bd570ff9 Daniel Borkmann    2016-04-18  317  
f428cc22 Daniel Borkmann    2016-07-13  318  	return __bpf_perf_event_output(regs, map, flags, &raw);
bd570ff9 Daniel Borkmann    2016-04-18 @319  }
bd570ff9 Daniel Borkmann    2016-04-18  320  
606274c5 Alexei Starovoitov 2016-07-06  321  static u64 bpf_get_current_task(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
606274c5 Alexei Starovoitov 2016-07-06  322  {

:::::: The code at line 319 was first introduced by commit
:::::: bd570ff970a54df653b48ed0cfb373f2ebed083d bpf: add event output helper for notifications/sampling/logging

:::::: TO: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
:::::: CC: David S. Miller <davem@xxxxxxxxxxxxx>

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