On Wed, Aug 18, 2021 at 11:07:43AM -0700, Yang Shi wrote:

On Mon, Aug 16, 2021 at 10:37 PM Naoya Horiguchi
[off-list ref] wrote:

quoted

From: Naoya Horiguchi <redacted>

HWPoisonHandlable() sometimes returns false for typical user pages
due to races with average memory events like transfers over LRU lists.
This causes failures in hwpoison handling.

There's retry code for such a case but does not work because the retry
loop reaches the retry limit too quickly before the page settles down to
handlable state. Let get_any_page() call shake_page() to fix it.

Fixes: 25182f05ffed ("mm,hwpoison: fix race with hugetlb page allocation")
Reported-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Naoya Horiguchi <redacted>
Cc: stable@vger.kernel.org # 5.13
---
 mm/memory-failure.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git v5.14-rc6/mm/memory-failure.c v5.14-rc6_patched/mm/memory-failure.c
index eefd823deb67..aa6592540f17 100644
--- v5.14-rc6/mm/memory-failure.c
+++ v5.14-rc6_patched/mm/memory-failure.c

@@ -1146,7 +1146,7 @@ static int __get_hwpoison_page(struct page *page)
         * unexpected races caused by taking a page refcount.
         */
        if (!HWPoisonHandlable(head))
-               return 0;
+               return -EBUSY;

        if (PageTransHuge(head)) {
                /*

@@ -1199,9 +1199,14 @@ static int get_any_page(struct page *p, unsigned long flags)
                        }
                        goto out;
                } else if (ret == -EBUSY) {
-                       /* We raced with freeing huge page to buddy, retry. */
-                       if (pass++ < 3)
+                       /*
+                        * We raced with (possibly temporary) unhandlable
+                        * page, retry.
+                        */
+                       if (pass++ < 3) {
+                               shake_page(p, 1);
                                goto try_again;
+                       }

I think the return value should be set to -EIO before jumping to out.
I'm supposed -EIO means this is really or very likely an unhandlable
page.

You're right, I have the same assumption that -EBUSY means transient error
and -EIO means permanent one. And we consider an error as permanent when the
retry limit is reached. I'll update the patch. Thank you for the comment.

- Naoya Horiguchi