[android-common:mirror-poly-aosp-pixel-malibu 4/4] fs/btrfs/subpage.c:332 btrfs_folio_end_lock_bitmap() warn: variable dereferenced before check 'fs_info' (see line 326)

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

BCC: lkp@intel.com
CC: oe-kbuild-all@lists.linux.dev
TO: cros-kernel-buildreports@googlegroups.com

tree:   https://android.googlesource.com/kernel/common mirror-poly-aosp-pixel-malibu
head:   9cbd7eeda1fe517f9ce3451fb3d7b4663df71429
commit: 0138f46fea3f5a250a5f49c33bd6174dec138369 [4/4] btrfs: rename btrfs_folio_(set|start|end)_writer_lock()
:::::: branch date: 20 hours ago
:::::: commit date: 1 year, 1 month ago
config: x86_64-randconfig-161-20260331 (https://download.01.org/0day-ci/archive/20260401/202604011348.FuiAdGBG-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
smatch: v0.5.0-9004-gb810ac53

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>
| Reported-by: Dan Carpenter <error27@gmail.com>
| Closes: https://lore.kernel.org/r/202604011348.FuiAdGBG-lkp@intel.com/

smatch warnings:
fs/btrfs/subpage.c:332 btrfs_folio_end_lock_bitmap() warn: variable dereferenced before check 'fs_info' (see line 326)

vim +/fs_info +332 fs/btrfs/subpage.c

1e1de38792e0ae2 Qu Wenruo 2021-05-31  321  
0138f46fea3f5a2 Qu Wenruo 2024-10-09  322  void btrfs_folio_end_lock_bitmap(const struct btrfs_fs_info *fs_info,
bd610c0937aaf03 Qu Wenruo 2024-09-02  323  				 struct folio *folio, unsigned long bitmap)
bd610c0937aaf03 Qu Wenruo 2024-09-02  324  {
bd610c0937aaf03 Qu Wenruo 2024-09-02  325  	struct btrfs_subpage *subpage = folio_get_private(folio);
bd610c0937aaf03 Qu Wenruo 2024-09-02 @326  	const int start_bit = fs_info->sectors_per_page * btrfs_bitmap_nr_locked;
bd610c0937aaf03 Qu Wenruo 2024-09-02  327  	unsigned long flags;
bd610c0937aaf03 Qu Wenruo 2024-09-02  328  	bool last = false;
bd610c0937aaf03 Qu Wenruo 2024-09-02  329  	int cleared = 0;
bd610c0937aaf03 Qu Wenruo 2024-09-02  330  	int bit;
bd610c0937aaf03 Qu Wenruo 2024-09-02  331  
bd610c0937aaf03 Qu Wenruo 2024-09-02 @332  	if (unlikely(!fs_info) || !btrfs_is_subpage(fs_info, folio->mapping)) {
bd610c0937aaf03 Qu Wenruo 2024-09-02  333  		folio_unlock(folio);
bd610c0937aaf03 Qu Wenruo 2024-09-02  334  		return;
bd610c0937aaf03 Qu Wenruo 2024-09-02  335  	}
bd610c0937aaf03 Qu Wenruo 2024-09-02  336  
0138f46fea3f5a2 Qu Wenruo 2024-10-09  337  	if (atomic_read(&subpage->nr_locked) == 0) {
0138f46fea3f5a2 Qu Wenruo 2024-10-09  338  		/* No subpage lock, locked by plain lock_page(). */
bd610c0937aaf03 Qu Wenruo 2024-09-02  339  		folio_unlock(folio);
bd610c0937aaf03 Qu Wenruo 2024-09-02  340  		return;
bd610c0937aaf03 Qu Wenruo 2024-09-02  341  	}
bd610c0937aaf03 Qu Wenruo 2024-09-02  342  
bd610c0937aaf03 Qu Wenruo 2024-09-02  343  	spin_lock_irqsave(&subpage->lock, flags);
bd610c0937aaf03 Qu Wenruo 2024-09-02  344  	for_each_set_bit(bit, &bitmap, fs_info->sectors_per_page) {
bd610c0937aaf03 Qu Wenruo 2024-09-02  345  		if (test_and_clear_bit(bit + start_bit, subpage->bitmaps))
bd610c0937aaf03 Qu Wenruo 2024-09-02  346  			cleared++;
bd610c0937aaf03 Qu Wenruo 2024-09-02  347  	}
0138f46fea3f5a2 Qu Wenruo 2024-10-09  348  	ASSERT(atomic_read(&subpage->nr_locked) >= cleared);
0138f46fea3f5a2 Qu Wenruo 2024-10-09  349  	last = atomic_sub_and_test(cleared, &subpage->nr_locked);
bd610c0937aaf03 Qu Wenruo 2024-09-02  350  	spin_unlock_irqrestore(&subpage->lock, flags);
bd610c0937aaf03 Qu Wenruo 2024-09-02  351  	if (last)
bd610c0937aaf03 Qu Wenruo 2024-09-02  352  		folio_unlock(folio);
bd610c0937aaf03 Qu Wenruo 2024-09-02  353  }
bd610c0937aaf03 Qu Wenruo 2024-09-02  354  

:::::: The code at line 332 was first introduced by commit
:::::: bd610c0937aaf03b2835638ada1fab8b0524c61a btrfs: only unlock the to-be-submitted ranges inside a folio

:::::: TO: Qu Wenruo <wqu@suse.com>
:::::: CC: David Sterba <dsterba@suse.com>

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki