The patch titled
Subject: mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED
has been added to the -mm tree. Its filename is
mmmadvise-call-soft_offline_page-without-mf_count_increased.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mmmadvise-call-soft_offline_page-without-mf_count_increased.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mmmadvise-call-soft_offline_page-without-mf_count_increased.patch
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------------------------------------------------------
From: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Subject: mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED
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.
Link: https://lkml.kernel.org/r/20201119105716.5962-4-osalvador@xxxxxxx
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/madvise.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)
--- a/mm/madvise.c~mmmadvise-call-soft_offline_page-without-mf_count_increased
+++ a/mm/madvise.c
@@ -900,20 +900,23 @@ static int madvise_inject_error(int beha
*/
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.
+ */
+ 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);
}
_
Patches currently in -mm which might be from naoya.horiguchi@xxxxxxx are
mmmadvise-call-soft_offline_page-without-mf_count_increased.patch
mmhwpoison-remove-mf_count_increased.patch
mmhwpoison-remove-flag-argument-from-soft-offline-functions.patch
