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hugetlb: add lockdep check for i_mmap_rwsem held in huge_pmd_share

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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 34ae204f18
("hugetlbfs: remove call to huge_pte_alloc without i_mmap_rwsem").

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew 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: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Mike Kravetz 2020-10-13 16:56:42 -07:00 committed by Linus Torvalds
parent 6664bfc8e9
commit 0bf7b64e6e
1 changed files with 11 additions and 4 deletions
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15
mm/hugetlb.c
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@ -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;