Re: [PATCH 4/8] mm: thp: only regular file could be THP eligible

[Dan Carpenter]

Hi Yang,

url:    https://github.com/0day-ci/linux/commits/Yang-Shi/Make-khugepaged-collapse-readonly-FS-THP-more-consistent/20220301-075903
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git dev
config: arm64-randconfig-m031-20220227 (https://download.01.org/0day-ci/archive/20220302/202203020034.2Ii9kTrs-lkp@xxxxxxxxx/config)
compiler: aarch64-linux-gcc (GCC) 11.2.0

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

smatch warnings:
include/linux/huge_mm.h:179 file_thp_enabled() warn: variable dereferenced before check 'vma->vm_file' (see line 177)
mm/khugepaged.c:468 hugepage_vma_check() error: we previously assumed 'vma->vm_file' could be null (see line 455)
include/linux/huge_mm.h:179 file_thp_enabled() warn: variable dereferenced before check 'vma->vm_file' (see line 177)

vim +179 include/linux/huge_mm.h

2224ed1155c07b Yang Shi     2022-02-28  175  static inline bool file_thp_enabled(struct vm_area_struct *vma)
2224ed1155c07b Yang Shi     2022-02-28  176  {
2224ed1155c07b Yang Shi     2022-02-28 @177  	struct inode *inode = vma->vm_file->f_inode;
                                                                      ^^^^^^^^^^^^^^
Dereference.

2224ed1155c07b Yang Shi     2022-02-28  178  
2224ed1155c07b Yang Shi     2022-02-28 @179  	return (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS)) && vma->vm_file &&
                                                                                                    ^^^^^^^^^^^^
Checked too late.

2224ed1155c07b Yang Shi     2022-02-28  180  	       (vma->vm_flags & VM_EXEC) &&
2224ed1155c07b Yang Shi     2022-02-28  181  	       !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
2224ed1155c07b Yang Shi     2022-02-28  182  }

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