mm/memory.c: simplify pfnmap_lockdep_assert

Use local `mapping' to reduce the pointer chasing.

akpm: extracted from a bugfix which Linus fixed with b1b4675 ("mm:
fix follow_pfnmap API lockdep assert").

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Manas <[email protected]>
Reviewed-by: Peter Xu <[email protected]>
Cc: Anup Sharma <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: weirdsmiley

mm/memory.c

@@ -6388,7 +6388,7 @@ static inline void pfnmap_lockdep_assert(struct vm_area_struct *vma)
 	struct address_space *mapping = file ? file->f_mapping : NULL;
 
 	if (mapping)
-		lockdep_assert(lockdep_is_held(&vma->vm_file->f_mapping->i_mmap_rwsem) ||
+		lockdep_assert(lockdep_is_held(&mapping->i_mmap_rwsem) ||
 			       lockdep_is_held(&vma->vm_mm->mmap_lock));
 	else
 		lockdep_assert(lockdep_is_held(&vma->vm_mm->mmap_lock));