[PATCH 4/5] mm/hmm: hmm_vma_fault() doesn't always call hmm_range_unregister()

[rcampbell]

From: Ralph Campbell <rcampbell@xxxxxxxxxx>

The helper function hmm_vma_fault() calls hmm_range_register() but is
missing a call to hmm_range_unregister() in one of the error paths.
This leads to a reference count leak and ultimately a memory leak on
struct hmm.

Always call hmm_range_unregister() if hmm_range_register() succeeded.

Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Balbir Singh <bsingharora@xxxxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
 include/linux/hmm.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 35a429621e1e..fa0671d67269 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -559,6 +559,7 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
 		return (int)ret;
 
 	if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
+		hmm_range_unregister(range);
 		/*
 		 * The mmap_sem was taken by driver we release it here and
 		 * returns -EAGAIN which correspond to mmap_sem have been
@@ -570,13 +571,13 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
 
 	ret = hmm_range_fault(range, block);
 	if (ret <= 0) {
+		hmm_range_unregister(range);
 		if (ret == -EBUSY || !ret) {
 			/* Same as above, drop mmap_sem to match old API. */
 			up_read(&range->vma->vm_mm->mmap_sem);
 			ret = -EBUSY;
 		} else if (ret == -EAGAIN)
 			ret = -EBUSY;
-		hmm_range_unregister(range);
 		return ret;
 	}
 	return 0;
-- 
2.20.1