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Subject[PATCH -V9 05/15] hugetlb: avoid taking i_mmap_mutex in unmap_single_vma() for hugetlb
Date
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

i_mmap_mutex lock was added in unmap_single_vma by 502717f4e ("hugetlb:
fix linked list corruption in unmap_hugepage_range()") but we don't use
page->lru in unmap_hugepage_range any more. Also the lock was taken
higher up in the stack in some code path. That would result in deadlock.

unmap_mapping_range (i_mmap_mutex)
-> unmap_mapping_range_tree
-> unmap_mapping_range_vma
-> zap_page_range_single
-> unmap_single_vma
-> unmap_hugepage_range (i_mmap_mutex)

For shared pagetable support for huge pages, since pagetable pages are ref
counted we don't need any lock during huge_pmd_unshare. We do take
i_mmap_mutex in huge_pmd_share while walking the vma_prio_tree in mapping.
(39dde65c9940c97f ("shared page table for hugetlb page")).

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
mm/memory.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 545e18a..f6bc04f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1326,11 +1326,8 @@ static void unmap_single_vma(struct mmu_gather *tlb,
* Since no pte has actually been setup, it is
* safe to do nothing in this case.
*/
- if (vma->vm_file) {
- mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);
+ if (vma->vm_file)
__unmap_hugepage_range(tlb, vma, start, end, NULL);
- mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
- }
} else
unmap_page_range(tlb, vma, start, end, details);
}
--
1.7.10


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