Commit 0bf7b64e authored by Mike Kravetz's avatar Mike Kravetz Committed by Linus Torvalds
Browse files

hugetlb: add lockdep check for i_mmap_rwsem held in huge_pmd_share 



As a debugging aid, huge_pmd_share should make sure i_mmap_rwsem is held
if necessary.  To clarify the 'if necessary', expand the comment block at
the beginning of huge_pmd_share.

No functional change.  The added i_mmap_assert_locked() call is only
enabled if CONFIG_LOCKDEP.

Ideally, this should have been included with commit 34ae204f
("hugetlbfs: remove call to huge_pte_alloc without i_mmap_rwsem").

Signed-off-by: default avatarMike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Link: https://lkml.kernel.org/r/20200911201248.88537-1-mike.kravetz@oracle.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6664bfc8

mm/hugetlb.c

+11 −4
Original line number Diff line number Diff line
@@ -5337,10 +5337,16 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, 
 * !shared pmd case because we can allocate the pmd later as well, it makes the

 * code much cleaner.

 *

 * This routine must be called with i_mmap_rwsem held in at least read mode.

 * For hugetlbfs, this prevents removal of any page table entries associated

 * with the address space.  This is important as we are setting up sharing

 * based on existing page table entries (mappings).

 * This routine must be called with i_mmap_rwsem held in at least read mode if

 * sharing is possible.  For hugetlbfs, this prevents removal of any page

 * table entries associated with the address space.  This is important as we

 * are setting up sharing based on existing page table entries (mappings).

 *

 * NOTE: This routine is only called from huge_pte_alloc.  Some callers of

 * huge_pte_alloc know that sharing is not possible and do not take

 * i_mmap_rwsem as a performance optimization.  This is handled by the

 * if !vma_shareable check at the beginning of the routine. i_mmap_rwsem is

 * only required for subsequent processing.

 */

pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)

{
@@ -5357,6 +5363,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) 
	if (!vma_shareable(vma, addr))

		return (pte_t *)pmd_alloc(mm, pud, addr);



	i_mmap_assert_locked(mapping);

	vma_interval_tree_foreach(svma, &mapping->i_mmap, idx, idx) {

		if (svma == vma)

			continue;