[PATCH] mm/khugepaged: fix issue with tracking lock

[Lorenzo Stoakes (Oracle)]

We are incorrectly treating lock_dropped to track both whether the lock is
currently held and whether or not the lock was ever dropped.

Update this change to account for this.

Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@xxxxxxxxxx>
---
 mm/khugepaged.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index d21348b85a59..b8452dbdb043 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2828,6 +2828,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
 	unsigned long hstart, hend, addr;
 	enum scan_result last_fail = SCAN_FAIL;
 	int thps = 0;
+	bool mmap_unlocked = false;

 	BUG_ON(vma->vm_start > start);
 	BUG_ON(vma->vm_end < end);
@@ -2850,10 +2851,11 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
 	for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
 		enum scan_result result = SCAN_FAIL;

-		if (*lock_dropped) {
+		if (mmap_unlocked) {
 			cond_resched();
 			mmap_read_lock(mm);
-			*lock_dropped = false;
+			mmap_unlocked = false;
+			*lock_dropped = true;
 			result = hugepage_vma_revalidate(mm, addr, false, &vma,
 							 cc);
 			if (result  != SCAN_SUCCEED) {
@@ -2864,7 +2866,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
 			hend = min(hend, vma->vm_end & HPAGE_PMD_MASK);
 		}

-		result = collapse_single_pmd(addr, vma, lock_dropped, cc);
+		result = collapse_single_pmd(addr, vma, &mmap_unlocked, cc);

 		switch (result) {
 		case SCAN_SUCCEED:
@@ -2893,8 +2895,10 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,

 out_maybelock:
 	/* Caller expects us to hold mmap_lock on return */
-	if (*lock_dropped)
+	if (mmap_unlocked) {
+		*lock_dropped = true;
 		mmap_read_lock(mm);
+	}
 out_nolock:
 	mmap_assert_locked(mm);
 	mmdrop(mm);
--
2.53.0