At page fault time, check i_private which indicates a fallocate hole punch
is in progress. If the fault falls within the hole, wait for the hole
punch operation to complete before proceeding with the fault.
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
mm/hugetlb.c | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3c7db92..540d3a79 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3580,6 +3580,7 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
struct page *pagecache_page = NULL;
struct hstate *h = hstate_vma(vma);
struct address_space *mapping;
+ struct inode *inode = file_inode(vma->vm_file);
int need_wait_lock = 0;
address &= huge_page_mask(h);
@@ -3603,6 +3604,42 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
idx = vma_hugecache_offset(h, vma, address);
/*
+ * page faults could race with fallocate hole punch. If a page
+ * is faulted between unmap and deallocation, it will still remain
+ * in the punched hole. During hole punch operations, a hugetlb_falloc
+ * structure will be pointed to by i_private. If this fault is for
+ * a page in a hole being punched, wait for the operation to finish
+ * before proceeding.
+ *
+ * Even with this strategy, it is still possible for a page fault to
+ * race with hole punch. However, the race window is considerably
+ * smaller.
+ */
+ if (unlikely(inode->i_private)) {
+ struct hugetlb_falloc *hugetlb_falloc;
+
+ spin_lock(&inode->i_lock);
+ hugetlb_falloc = inode->i_private;
+ if (hugetlb_falloc && hugetlb_falloc->waitq &&
+ idx >= hugetlb_falloc->start &&
+ idx <= hugetlb_falloc->end) {
+ wait_queue_head_t *hugetlb_falloc_waitq;
+ DEFINE_WAIT(hugetlb_fault_wait);
+
+ hugetlb_falloc_waitq = hugetlb_falloc->waitq;
+ prepare_to_wait(hugetlb_falloc_waitq,
+ &hugetlb_fault_wait,
+ TASK_UNINTERRUPTIBLE);
+ spin_unlock(&inode->i_lock);
+ schedule();
+
+ spin_lock(&inode->i_lock);
+ finish_wait(hugetlb_falloc_waitq, &hugetlb_fault_wait);
+ }
+ spin_unlock(&inode->i_lock);
+ }
+
+ /*
* Serialize hugepage allocation and instantiation, so that we don't
* get spurious allocation failures if two CPUs race to instantiate
* the same page in the page cache.
--
2.4.3
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