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

From: Ralph Campbell
Date: Tue May 07 2019 - 14:13:21 EST

On 5/7/19 6:15 AM, Souptick Joarder wrote:
On Tue, May 7, 2019 at 5:00 AM <rcampbell@xxxxxxxxxx> wrote:

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.

How about * Call hmm_range_unregister() in error path if
hmm_range_register() succeeded* ?

Sure, sounds good.
I'll include that in v2.

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);

what is the reason to moved it up ?

I moved it up because the normal calling pattern is:

I don't think it is a bug to unlock mmap_sem and then unregister,
it is just more consistent nesting.

if (ret == -EBUSY || !ret) {
/* Same as above, drop mmap_sem to match old API. */
ret = -EBUSY;
} else if (ret == -EAGAIN)
ret = -EBUSY;
- hmm_range_unregister(range);
return ret;
return 0;