kernel/cgroup/rstat.c:166:22: warning: no previous declaration for 'bpf_rstat_flush'

[kernel test robot <lkp@intel.com>]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   4853c74bd7ab7fdb83f319bd9ace8a08c031e9b6
commit: a319185be9f5ad13c2a296d448ac52ffe45d194c cgroup: bpf: enable bpf programs to integrate with rstat
date:   12 months ago
config: i386-randconfig-r025-20230817 (https://download.01.org/0day-ci/archive/20230817/202308170617.MHUk8MPr-lkp@intel.com/config)
compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
reproduce: (https://download.01.org/0day-ci/archive/20230817/202308170617.MHUk8MPr-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202308170617.MHUk8MPr-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	

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