[peterz-queue:perf/core 10/15] kernel/events/core.c:7018:6: warning: variable 'user_extra' is used uninitialized whenever 'if' condition is true

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

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/core
head:   965dafe6500a2b46311c810c9360c29c15e45677
commit: 189c97b1b2ab5bf33bdf635a70631526f1cd1bfd [10/15] perf: Split out the AUX buffer allocation
config: x86_64-buildonly-randconfig-003-20250811 (https://download.01.org/0day-ci/archive/20250812/202508120028.0P5MnCYq-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/20250812/202508120028.0P5MnCYq-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/202508120028.0P5MnCYq-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/events/core.c:7018:6: warning: variable 'user_extra' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
    7018 |         if (rb_has_aux(rb)) {
         |             ^~~~~~~~~~~~~~
   kernel/events/core.c:7043:25: note: uninitialized use occurs here
    7043 |         perf_mmap_account(vma, user_extra, extra);
         |                                ^~~~~~~~~~
   kernel/events/core.c:7018:2: note: remove the 'if' if its condition is always false
    7018 |         if (rb_has_aux(rb)) {
         |         ^~~~~~~~~~~~~~~~~~~~~
    7019 |                 atomic_inc(&rb->aux_mmap_count);
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    7020 | 
    7021 |         } else {
         |         ~~~~~~
   kernel/events/core.c:6978:17: note: initialize the variable 'user_extra' to silence this warning
    6978 |         long user_extra, extra;
         |                        ^
         |                         = 0
>> kernel/events/core.c:7018:6: warning: variable 'extra' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
    7018 |         if (rb_has_aux(rb)) {
         |             ^~~~~~~~~~~~~~
   kernel/events/core.c:7043:37: note: uninitialized use occurs here
    7043 |         perf_mmap_account(vma, user_extra, extra);
         |                                            ^~~~~
   kernel/events/core.c:7018:2: note: remove the 'if' if its condition is always false
    7018 |         if (rb_has_aux(rb)) {
         |         ^~~~~~~~~~~~~~~~~~~~~
    7019 |                 atomic_inc(&rb->aux_mmap_count);
         |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    7020 | 
    7021 |         } else {
         |         ~~~~~~
   kernel/events/core.c:6978:24: note: initialize the variable 'extra' to silence this warning
    6978 |         long user_extra, extra;
         |                               ^
         |                                = 0
   kernel/events/core.c:215:20: warning: unused function 'class_perf_ctx_lock_destructor' [-Wunused-function]
     215 | static inline void class_perf_ctx_lock_destructor(class_perf_ctx_lock_t *_T)
         |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   kernel/events/core.c:219:1: warning: unused function 'class_perf_ctx_lock_constructor' [-Wunused-function]
     219 | class_perf_ctx_lock_constructor(struct perf_cpu_context *cpuctx,
         | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   4 warnings generated.


vim +7018 kernel/events/core.c

  6972	
  6973	static int perf_mmap_aux(struct vm_area_struct *vma, struct perf_event *event,
  6974				 unsigned long nr_pages)
  6975	{
  6976		u64 aux_offset, aux_size;
  6977		struct perf_buffer *rb;
  6978		long user_extra, extra;
  6979		int ret, rb_flags = 0;
  6980	
  6981		rb = event->rb;
  6982		if (!rb)
  6983			return -EINVAL;
  6984	
  6985		guard(mutex)(&rb->aux_mutex);
  6986	
  6987		/*
  6988		 * AUX area mapping: if rb->aux_nr_pages != 0, it's already
  6989		 * mapped, all subsequent mappings should have the same size
  6990		 * and offset. Must be above the normal perf buffer.
  6991		 */
  6992		aux_offset = READ_ONCE(rb->user_page->aux_offset);
  6993		aux_size = READ_ONCE(rb->user_page->aux_size);
  6994	
  6995		if (aux_offset < perf_data_size(rb) + PAGE_SIZE)
  6996			return -EINVAL;
  6997	
  6998		if (aux_offset != vma->vm_pgoff << PAGE_SHIFT)
  6999			return -EINVAL;
  7000	
  7001		/* already mapped with a different offset */
  7002		if (rb_has_aux(rb) && rb->aux_pgoff != vma->vm_pgoff)
  7003			return -EINVAL;
  7004	
  7005		if (aux_size != nr_pages * PAGE_SIZE)
  7006			return -EINVAL;
  7007	
  7008		/* already mapped with a different size */
  7009		if (rb_has_aux(rb) && rb->aux_nr_pages != nr_pages)
  7010			return -EINVAL;
  7011	
  7012		if (!is_power_of_2(nr_pages))
  7013			return -EINVAL;
  7014	
  7015		if (!atomic_inc_not_zero(&rb->mmap_count))
  7016			return -EINVAL;
  7017	
> 7018		if (rb_has_aux(rb)) {
  7019			atomic_inc(&rb->aux_mmap_count);
  7020	
  7021		} else {
  7022			if (!perf_mmap_calc_limits(vma, &user_extra, &extra)) {
  7023				atomic_dec(&rb->mmap_count);
  7024				return -EPERM;
  7025			}
  7026	
  7027			WARN_ON(!rb && event->rb);
  7028	
  7029			if (vma->vm_flags & VM_WRITE)
  7030				rb_flags |= RING_BUFFER_WRITABLE;
  7031	
  7032			ret = rb_alloc_aux(rb, event, vma->vm_pgoff, nr_pages,
  7033					   event->attr.aux_watermark, rb_flags);
  7034			if (ret) {
  7035				atomic_dec(&rb->mmap_count);
  7036				return ret;
  7037			}
  7038	
  7039			atomic_set(&rb->aux_mmap_count, 1);
  7040			rb->aux_mmap_locked = extra;
  7041		}
  7042	
  7043		perf_mmap_account(vma, user_extra, extra);
  7044		atomic_inc(&event->mmap_count);
  7045	
  7046		return 0;
  7047	}
  7048	

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