On 11/19/20 11:57 AM, Oscar Salvador wrote:
From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
The call to get_user_pages_fast is only to get the pointer to a struct
page of a given address, pinning it is memory-poisoning handler's job,
so drop the refcount grabbed by get_user_pages_fast().
Note that the target page is still pinned after this put_page() because
the current process should have refcount from mapping.
Well, but can't it go away due to reclaim, migration or whatever?
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
---
mm/madvise.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)
diff --git a/mm/madvise.c b/mm/madvise.c
index c6b5524add58..7a0f64b93635 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -900,20 +900,23 @@ static int madvise_inject_error(int behavior,
*/
size = page_size(compound_head(page));
+ /*
+ * The get_user_pages_fast() is just to get the pfn of the
+ * given address, and the refcount has nothing to do with
+ * what we try to test, so it should be released immediately.
+ * This is racy but it's intended because the real hardware
+ * errors could happen at any moment and memory error handlers
+ * must properly handle the race.
Sure they have to. We might just be unexpectedly messing with other process'
memory. Or does anything else prevent that?
+ */
+ put_page(page);
+
if (behavior == MADV_SOFT_OFFLINE) {
pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
pfn, start);
- ret = soft_offline_page(pfn, MF_COUNT_INCREASED);
+ ret = soft_offline_page(pfn, 0);
} else {
pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
pfn, start);
- /*
- * Drop the page reference taken by get_user_pages_fast(). In
- * the absence of MF_COUNT_INCREASED the memory_failure()
- * routine is responsible for pinning the page to prevent it
- * from being released back to the page allocator.
- */
- put_page(page);
ret = memory_failure(pfn, 0);
}
