[tglx-devel:core/rseq 5/11] kernel/sched/membarrier.c:208:6: error: call to undeclared function 'rseq_v2'; ISO C99 and later do not support implicit function declarations

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

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git core/rseq
head:   9a2253d7640f6b319562dda1a87cee3416c5d332
commit: a86e32c235afd7ea34ee7ecca5ce532b918930c2 [5/11] rseq: Revert to historical performance killing behaviour
config: um-allnoconfig (https://download.01.org/0day-ci/archive/20260430/202604300311.aIKKS59R-lkp@intel.com/config)
compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 5bac06718f502014fade905512f1d26d578a18f3)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260430/202604300311.aIKKS59R-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/202604300311.aIKKS59R-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from kernel/sched/build_utility.c:97:
>> kernel/sched/membarrier.c:208:6: error: call to undeclared function 'rseq_v2'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     208 |         if (rseq_v2(current))
         |             ^
   1 error generated.


vim +/rseq_v2 +208 kernel/sched/membarrier.c

   191	
   192	static void ipi_rseq(void *info)
   193	{
   194		/*
   195		 * Ensure that all stores done by the calling thread are visible
   196		 * to the current task before the current task resumes.  We could
   197		 * probably optimize this away on most architectures, but by the
   198		 * time we've already sent an IPI, the cost of the extra smp_mb()
   199		 * is negligible.
   200		 */
   201		smp_mb();
   202		/*
   203		 * Legacy mode requires that IDs are written and the critical section is
   204		 * evaluated. V2 optimized mode handles the critical section and IDs are
   205		 * only updated if they change as a consequence of preemption after
   206		 * return from this IPI.
   207		 */
 > 208		if (rseq_v2(current))
   209			rseq_sched_switch_event(current);
   210		else
   211			rseq_force_update();
   212	}
   213	

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