linux-kernel - Re: kernel/cgroup/rstat.c:166:22: warning: no previous declaration for 'bpf_rstat

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Date:   Thu, 2 Nov 2023 18:58:30 +0800
From:   Philip Li <philip.li@...el.com>
To:     kernel test robot <lkp@...el.com>
CC:     Yosry Ahmed <yosryahmed@...gle.com>,
        <oe-kbuild-all@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Hao Luo <haoluo@...gle.com>
Subject: Re: kernel/cgroup/rstat.c:166:22: warning: no previous declaration
 for 'bpf_rstat_flush'

On Thu, Nov 02, 2023 at 06:13:13PM +0800, kernel test robot wrote:
> Hi Yosry,

Sorry for the false report, kindly ignore this one. We will resolve the
problem shortly.

> 
> FYI, the error/warning still remains.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   21e80f3841c01aeaf32d7aee7bbc87b3db1aa0c6
> commit: a319185be9f5ad13c2a296d448ac52ffe45d194c cgroup: bpf: enable bpf programs to integrate with rstat
> date:   1 year, 2 months ago
> config: um-i386_defconfig (https://download.01.org/0day-ci/archive/20231102/202311021859.z3HikNTw-lkp@intel.com/config)
> compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231102/202311021859.z3HikNTw-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202311021859.z3HikNTw-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> kernel/cgroup/rstat.c:166:22: warning: no previous declaration for 'bpf_rstat_flush' [-Wmissing-declarations]
>     __weak noinline void bpf_rstat_flush(struct cgroup *cgrp,
>                          ^~~~~~~~~~~~~~~
> 
> 
> vim +/bpf_rstat_flush +166 kernel/cgroup/rstat.c
> 
>    147	
>    148	/*
>    149	 * A hook for bpf stat collectors to attach to and flush their stats.
>    150	 * Together with providing bpf kfuncs for cgroup_rstat_updated() and
>    151	 * cgroup_rstat_flush(), this enables a complete workflow where bpf progs that
>    152	 * collect cgroup stats can integrate with rstat for efficient flushing.
>    153	 *
>    154	 * A static noinline declaration here could cause the compiler to optimize away
>    155	 * the function. A global noinline declaration will keep the definition, but may
>    156	 * optimize away the callsite. Therefore, __weak is needed to ensure that the
>    157	 * call is still emitted, by telling the compiler that we don't know what the
>    158	 * function might eventually be.
>    159	 *
>    160	 * __diag_* below are needed to dismiss the missing prototype warning.
>    161	 */
>    162	__diag_push();
>    163	__diag_ignore_all("-Wmissing-prototypes",
>    164			  "kfuncs which will be used in BPF programs");
>    165	
>  > 166	__weak noinline void bpf_rstat_flush(struct cgroup *cgrp,
>    167					     struct cgroup *parent, int cpu)
>    168	{
>    169	}
>    170	
> 
> -- 
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki
>