[RFC v3 PATCH 04/10] mm/hugetlb: expose hugetlb fault mutex for use by fallocate

[Mike Kravetz <mike.kravetz@oracle.com>]

hugetlb page faults are currently synchronized by the table of
mutexes (htlb_fault_mutex_table).  fallocate code will need to
synchronize with the page fault code when it allocates or
deletes pages.  Expose interfaces so that fallocate operations
can be synchronized with page faults.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
 include/linux/hugetlb.h |  3 +++
 mm/hugetlb.c            | 23 ++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index fd337f2..d0d033e 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -82,6 +82,9 @@ void putback_active_hugepage(struct page *page);
 bool is_hugepage_active(struct page *page);
 void free_huge_page(struct page *page);
 void hugetlb_fix_reserve_counts(struct inode *inode, bool restore_reserve);
+u32 hugetlb_fault_mutex_shared_hash(struct address_space *mapping, pgoff_t idx);
+void hugetlb_fault_mutex_lock(u32 hash);
+void hugetlb_fault_mutex_unlock(u32 hash);
 
 #ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
 pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 620cc9e..df0d32a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3183,7 +3183,8 @@ static u32 fault_mutex_hash(struct hstate *h, struct mm_struct *mm,
 	unsigned long key[2];
 	u32 hash;
 
-	if (vma->vm_flags & VM_SHARED) {
+	/* !vma implies this was called from hugetlbfs fallocate code */
+	if (!vma || vma->vm_flags & VM_SHARED) {
 		key[0] = (unsigned long) mapping;
 		key[1] = idx;
 	} else {
@@ -3209,6 +3210,26 @@ static u32 fault_mutex_hash(struct hstate *h, struct mm_struct *mm,
 }
 #endif
 
+/*
+ * Interfaces to the fault mutex routines for use by hugetlbfs
+ * fallocate code.  Faults must be synchronized with page adds or
+ * deletes by fallocate.  fallocate only deals with shared mappings.
+ */
+u32 hugetlb_fault_mutex_shared_hash(struct address_space *mapping, pgoff_t idx)
+{
+	return fault_mutex_hash(NULL, NULL, NULL, mapping, idx, 0);
+}
+
+void hugetlb_fault_mutex_lock(u32 hash)
+{
+	mutex_lock(&htlb_fault_mutex_table[hash]);
+}
+
+void hugetlb_fault_mutex_unlock(u32 hash)
+{
+	mutex_unlock(&htlb_fault_mutex_table[hash]);
+}
+
 int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 			unsigned long address, unsigned int flags)
 {
-- 
2.1.0

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