[PATCH] mm/hugetlb: Unmap pages if page fault raced with hole punch

[Mike Kravetz]

This patch is a combination of:
[PATCH v2 4/4] mm/hugetlb: Unmap pages to remove if page fault raced
	with hole punch  and,
[PATCH] mm/hugetlb: i_mmap_lock_write before unmapping in
	remove_inode_hugepages
This patch can replace the entire series:
[PATCH v2 0/4] hugetlbfs fallocate hole punch race with page faults
	and
[PATCH] mm/hugetlb: i_mmap_lock_write before unmapping in
	remove_inode_hugepages
It is being provided in an effort to possibly make tree management easier.

Page faults can race with fallocate hole punch.  If a page fault happens
between the unmap and remove operations, the page is not removed and
remains within the hole.  This is not the desired behavior.

If this race is detected and a page is mapped, the remove operation
(remove_inode_hugepages) will unmap the page before removing.  The unmap
within remove_inode_hugepages occurs with the hugetlb_fault_mutex held
so that no other faults can occur until the page is removed.

The (unmodified) routine hugetlb_vmdelete_list was moved ahead of
remove_inode_hugepages to satisfy the new reference.

Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
 fs/hugetlbfs/inode.c | 125 ++++++++++++++++++++++++++-------------------------
 1 file changed, 65 insertions(+), 60 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 316adb9..8b8e5e8 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -324,11 +324,44 @@ static void remove_huge_page(struct page *page)
 	delete_from_page_cache(page);
 }
 
+static inline void
+hugetlb_vmdelete_list(struct rb_root *root, pgoff_t start, pgoff_t end)
+{
+	struct vm_area_struct *vma;
+
+	/*
+	 * end == 0 indicates that the entire range after
+	 * start should be unmapped.
+	 */
+	vma_interval_tree_foreach(vma, root, start, end ? end : ULONG_MAX) {
+		unsigned long v_offset;
+
+		/*
+		 * Can the expression below overflow on 32-bit arches?
+		 * No, because the interval tree returns us only those vmas
+		 * which overlap the truncated area starting at pgoff,
+		 * and no vma on a 32-bit arch can span beyond the 4GB.
+		 */
+		if (vma->vm_pgoff < start)
+			v_offset = (start - vma->vm_pgoff) << PAGE_SHIFT;
+		else
+			v_offset = 0;
+
+		if (end) {
+			end = ((end - start) << PAGE_SHIFT) +
+			       vma->vm_start + v_offset;
+			if (end > vma->vm_end)
+				end = vma->vm_end;
+		} else
+			end = vma->vm_end;
+
+		unmap_hugepage_range(vma, vma->vm_start + v_offset, end, NULL);
+	}
+}
 
 /*
  * remove_inode_hugepages handles two distinct cases: truncation and hole
  * punch.  There are subtle differences in operation for each case.
-
  * truncation is indicated by end of range being LLONG_MAX
  *	In this case, we first scan the range and release found pages.
  *	After releasing pages, hugetlb_unreserve_pages cleans up region/reserv
@@ -381,12 +414,27 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 		for (i = 0; i < pagevec_count(&pvec); ++i) {
 			struct page *page = pvec.pages[i];
 			u32 hash;
+			bool rsv_on_error;
 
 			hash = hugetlb_fault_mutex_hash(h, current->mm,
 							&pseudo_vma,
 							mapping, next, 0);
 			mutex_lock(&hugetlb_fault_mutex_table[hash]);
 
+			/*
+			 * If page is mapped, it was faulted in after being
+			 * unmapped in caller.  Unmap (again) now after taking
+			 * the fault mutex.  The mutex will prevent faults
+			 * until we finish removing the page.
+			 */
+			if (page_mapped(page)) {
+				i_mmap_lock_write(mapping);
+				hugetlb_vmdelete_list(&mapping->i_mmap,
+					next * pages_per_huge_page(h),
+					(next + 1) * pages_per_huge_page(h));
+				i_mmap_unlock_write(mapping);
+			}
+
 			lock_page(page);
 			if (page->index >= end) {
 				unlock_page(page);
@@ -396,31 +444,23 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
 			}
 
 			/*
-			 * If page is mapped, it was faulted in after being
-			 * unmapped.  Do nothing in this race case.  In the
-			 * normal case page is not mapped.
+			 * We must free the huge page and remove from page
+			 * cache (remove_huge_page) BEFORE removing the
+			 * region/reserve map (hugetlb_unreserve_pages).
+			 * In rare out of memory conditions, removal of the
+			 * region/reserve map could fail.  Before free'ing
+			 * the page, note PagePrivate which is used in case
+			 * of error.
 			 */
-			if (!page_mapped(page)) {
-				bool rsv_on_error = !PagePrivate(page);
-				/*
-				 * We must free the huge page and remove
-				 * from page cache (remove_huge_page) BEFORE
-				 * removing the region/reserve map
-				 * (hugetlb_unreserve_pages).  In rare out
-				 * of memory conditions, removal of the
-				 * region/reserve map could fail.  Before
-				 * free'ing the page, note PagePrivate which
-				 * is used in case of error.
-				 */
-				remove_huge_page(page);
-				freed++;
-				if (!truncate_op) {
-					if (unlikely(hugetlb_unreserve_pages(
-							inode, next,
-							next + 1, 1)))
-						hugetlb_fix_reserve_counts(
-							inode, rsv_on_error);
-				}
+			rsv_on_error = !PagePrivate(page);
+			remove_huge_page(page);
+			freed++;
+			if (!truncate_op) {
+				if (unlikely(hugetlb_unreserve_pages(inode,
+								next, next + 1,
+								1)))
+					hugetlb_fix_reserve_counts(inode,
+								rsv_on_error);
 			}
 
 			if (page->index > next)
@@ -450,41 +490,6 @@ static void hugetlbfs_evict_inode(struct inode *inode)
 	clear_inode(inode);
 }
 
-static inline void
-hugetlb_vmdelete_list(struct rb_root *root, pgoff_t start, pgoff_t end)
-{
-	struct vm_area_struct *vma;
-
-	/*
-	 * end == 0 indicates that the entire range after
-	 * start should be unmapped.
-	 */
-	vma_interval_tree_foreach(vma, root, start, end ? end : ULONG_MAX) {
-		unsigned long v_offset;
-
-		/*
-		 * Can the expression below overflow on 32-bit arches?
-		 * No, because the interval tree returns us only those vmas
-		 * which overlap the truncated area starting at pgoff,
-		 * and no vma on a 32-bit arch can span beyond the 4GB.
-		 */
-		if (vma->vm_pgoff < start)
-			v_offset = (start - vma->vm_pgoff) << PAGE_SHIFT;
-		else
-			v_offset = 0;
-
-		if (end) {
-			end = ((end - start) << PAGE_SHIFT) +
-			       vma->vm_start + v_offset;
-			if (end > vma->vm_end)
-				end = vma->vm_end;
-		} else
-			end = vma->vm_end;
-
-		unmap_hugepage_range(vma, vma->vm_start + v_offset, end, NULL);
-	}
-}
-
 static int hugetlb_vmtruncate(struct inode *inode, loff_t offset)
 {
 	pgoff_t pgoff;
-- 
2.4.3

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