[gourryinverse:scratch/gourry/isolation/linus 6/10] kernel/cgroup/cpuset.c:4339:13: warning: variable 'allowed' is used uninitialized whenever 'if' condition is false

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

tree:   https://github.com/gourryinverse/linux scratch/gourry/isolation/linus
head:   c74a85115777a0e4ff7ba671c4631adb4ba32ecc
commit: 81b4628c13856d1bc84678ed6655180ca0554688 [6/10] cpuset: introduce cpuset.mems.default
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20251111/202511112256.k3RvmZ7Q-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251111/202511112256.k3RvmZ7Q-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/202511112256.k3RvmZ7Q-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/cgroup/cpuset.c:4339:13: warning: variable 'allowed' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
    4339 |         } else if (node_isset(node, current->mems_default))
         |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/nodemask.h:149:36: note: expanded from macro 'node_isset'
     149 | #define node_isset(node, nodemask) test_bit((node), (nodemask).bits)
         |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/bitops.h:60:29: note: expanded from macro 'test_bit'
      60 | #define test_bit(nr, addr)              bitop(_test_bit, nr, addr)
         |                                         ^~~~~~~~~~~~~~~~~~~~~~~~~~
   include/linux/bitops.h:43:2: note: expanded from macro 'bitop'
      43 |         ((__builtin_constant_p(nr) &&                                   \
         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      44 |           __builtin_constant_p((uintptr_t)(addr) != (uintptr_t)NULL) && \
         |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      45 |           (uintptr_t)(addr) != (uintptr_t)NULL &&                       \
         |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      46 |           __builtin_constant_p(*(const unsigned long *)(addr))) ?       \
         |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      47 |          const##op(nr, addr) : op(nr, addr))
         |          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   kernel/cgroup/cpuset.c:4342:6: note: uninitialized use occurs here
    4342 |         if (allowed)
         |             ^~~~~~~
   kernel/cgroup/cpuset.c:4339:9: note: remove the 'if' if its condition is always true
    4339 |         } else if (node_isset(node, current->mems_default))
         |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    4340 |                 allowed = true;
   kernel/cgroup/cpuset.c:4327:14: note: initialize the variable 'allowed' to silence this warning
    4327 |         bool allowed;                   /* is allocation in zone z allowed? */
         |                     ^
         |                      = 0
   1 warning generated.


vim +4339 kernel/cgroup/cpuset.c

  4282	
  4283	/*
  4284	 * cpuset_current_node_allowed - Can current task allocate on a memory node?
  4285	 * @node: is this an allowed node?
  4286	 * @gfp_mask: memory allocation flags
  4287	 *
  4288	 * If we're in interrupt, yes, we can always allocate.  If @node is set in
  4289	 * current's mems_default, yes.  If it's not a __GFP_HARDWALL request and this
  4290	 * node is set in the nearest hardwalled cpuset ancestor to current's cpuset,
  4291	 * yes.  If current has access to memory reserves as an oom victim, yes.
  4292	 * Otherwise, no.
  4293	 *
  4294	 * GFP_USER allocations are marked with the __GFP_HARDWALL bit,
  4295	 * and do not allow allocations outside the current tasks cpuset
  4296	 * unless the task has been OOM killed.
  4297	 * GFP_KERNEL allocations are not so marked, so can escape to the
  4298	 * nearest enclosing hardwalled ancestor cpuset.
  4299	 *
  4300	 * Scanning up parent cpusets requires callback_lock.  The
  4301	 * __alloc_pages() routine only calls here with __GFP_HARDWALL bit
  4302	 * _not_ set if it's a GFP_KERNEL allocation, and all nodes in the
  4303	 * current tasks mems_default came up empty on the first pass over
  4304	 * the zonelist.  So only GFP_KERNEL allocations, if all nodes in the
  4305	 * cpuset are short of memory, might require taking the callback_lock.
  4306	 *
  4307	 * The first call here from mm/page_alloc:get_page_from_freelist()
  4308	 * has __GFP_HARDWALL set in gfp_mask, enforcing hardwall cpusets,
  4309	 * so no allocation on a node outside the cpuset is allowed (unless
  4310	 * in interrupt, of course).
  4311	 *
  4312	 * The second pass through get_page_from_freelist() doesn't even call
  4313	 * here for GFP_ATOMIC calls.  For those calls, the __alloc_pages()
  4314	 * variable 'wait' is not set, and the bit ALLOC_CPUSET is not set
  4315	 * in alloc_flags.  That logic and the checks below have the combined
  4316	 * affect that:
  4317	 *	in_interrupt - any node ok (current task context irrelevant)
  4318	 *	GFP_ATOMIC   - any node ok
  4319	 *	tsk_is_oom_victim   - any node ok
  4320	 *	GFP_KERNEL   - any node in enclosing hardwalled cpuset ok
  4321	 *	GFP_USER     - only nodes in current tasks mems allowed ok.
  4322	 *	GFP_PROTECTED - allow non-sysram nodes in mems_allowed
  4323	 */
  4324	bool cpuset_current_node_allowed(int node, gfp_t gfp_mask)
  4325	{
  4326		struct cpuset *cs;		/* current cpuset ancestors */
  4327		bool allowed;			/* is allocation in zone z allowed? */
  4328		unsigned long flags;
  4329		bool protected_node = gfp_mask & __GFP_PROTECTED;
  4330	
  4331		if (in_interrupt())
  4332			return true;
  4333	
  4334		if (protected_node) {
  4335			rcu_read_lock();
  4336			cs = task_cs(current);
  4337			allowed = node_isset(node, cs->mems_allowed);
  4338			rcu_read_unlock();
> 4339		} else if (node_isset(node, current->mems_default))
  4340			allowed = true;
  4341	
  4342		if (allowed)
  4343			return allowed;
  4344	
  4345		/*
  4346		 * Allow tasks that have access to memory reserves because they have
  4347		 * been OOM killed to get memory anywhere.
  4348		 */
  4349		if (unlikely(tsk_is_oom_victim(current)))
  4350			return true;
  4351		if (gfp_mask & __GFP_HARDWALL)	/* If hardwall request, stop here */
  4352			return false;
  4353	
  4354		if (current->flags & PF_EXITING) /* Let dying task have memory */
  4355			return true;
  4356	
  4357		/* Not hardwall and node outside mems_allowed: scan up cpusets */
  4358		spin_lock_irqsave(&callback_lock, flags);
  4359	
  4360		cs = nearest_hardwall_ancestor(task_cs(current));
  4361		allowed = node_isset(node, cs->mems_allowed); /* include protected */
  4362		if (!protected_node && !nodes_empty(mt_sysram_nodelist))
  4363			allowed &= node_isset(node, mt_sysram_nodelist);
  4364	
  4365		spin_unlock_irqrestore(&callback_lock, flags);
  4366		return allowed;
  4367	}
  4368	

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