+ mm-memory-failure-send-sigbus-in-the-event-of-thp-split-fail.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/memory-failure: send SIGBUS in the event of thp split fail
has been added to the -mm mm-unstable branch.  Its filename is
     mm-memory-failure-send-sigbus-in-the-event-of-thp-split-fail.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory-failure-send-sigbus-in-the-event-of-thp-split-fail.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Jane Chu <jane.chu@oracle.com>
Subject: mm/memory-failure: send SIGBUS in the event of thp split fail
Date: Fri, 24 May 2024 15:53:06 -0600

While handling hwpoison in a THP page, it is possible that
try_to_split_thp_page() fails.  For example, when the THP page has been
RDMA pinned.  At this point, the kernel cannot isolate the poisoned THP
page, all it could do is to send a SIGBUS to the user process with
meaningful payload to give user-level recovery a chance.

Link: https://lkml.kernel.org/r/20240524215306.2705454-6-jane.chu@oracle.com
Signed-off-by: Jane Chu <jane.chu@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Oscar Salvador <oalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/memory-failure.c |   34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

--- a/mm/memory-failure.c~mm-memory-failure-send-sigbus-in-the-event-of-thp-split-fail
+++ a/mm/memory-failure.c
@@ -1706,7 +1706,12 @@ static int identify_page_state(unsigned
 	return page_action(ps, p, pfn);
 }
 
-static int try_to_split_thp_page(struct page *page)
+/*
+ * When 'release' is 'false', it means that if thp split has failed,
+ * there is still more to do, hence the page refcount we took earlier
+ * is still needed.
+ */
+static int try_to_split_thp_page(struct page *page, bool release)
 {
 	int ret;
 
@@ -1714,7 +1719,7 @@ static int try_to_split_thp_page(struct
 	ret = split_huge_page(page);
 	unlock_page(page);
 
-	if (unlikely(ret))
+	if (ret && release)
 		put_page(page);
 
 	return ret;
@@ -2186,6 +2191,22 @@ out:
 	return rc;
 }
 
+/*
+ * The calling condition is as such: thp split failed, page might have
+ * been RDMA pinned, not much can be done for recovery.
+ * But a SIGBUS should be delivered with vaddr provided so that the user
+ * application has a chance to recover. Also, application processes'
+ * election for MCE early killed will be honored.
+ */
+static void kill_procs_now(struct page *p, unsigned long pfn, int flags,
+				struct folio *folio)
+{
+	LIST_HEAD(tokill);
+
+	collect_procs(folio, p, &tokill, flags & MF_ACTION_REQUIRED);
+	kill_procs(&tokill, true, pfn, flags);
+}
+
 /**
  * memory_failure - Handle memory failure of a page.
  * @pfn: Page Number of the corrupted page
@@ -2327,8 +2348,11 @@ try_again:
 		 * page is a valid handlable page.
 		 */
 		folio_set_has_hwpoisoned(folio);
-		if (try_to_split_thp_page(p) < 0) {
-			res = action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
+		if (try_to_split_thp_page(p, false) < 0) {
+			res = -EHWPOISON;
+			kill_procs_now(p, pfn, flags, folio);
+			put_page(p);
+			action_result(pfn, MF_MSG_UNSPLIT_THP, MF_FAILED);
 			goto unlock_mutex;
 		}
 		VM_BUG_ON_PAGE(!page_count(p), p);
@@ -2702,7 +2726,7 @@ static int soft_offline_in_use_page(stru
 	};
 
 	if (!huge && folio_test_large(folio)) {
-		if (try_to_split_thp_page(page)) {
+		if (try_to_split_thp_page(page, true)) {
 			pr_info("soft offline: %#lx: thp split failed\n", pfn);
 			return -EBUSY;
 		}
_

Patches currently in -mm which might be from jane.chu@oracle.com are

mm-memory-failure-try-to-send-sigbus-even-if-unmap-failed.patch
mm-madvise-add-mf_action_required-to-madvisemadv_hwpoison.patch
mm-memory-failure-improve-memory-failure-action_result-messages.patch
mm-memory-failure-move-hwpoison_filter-higher-up.patch
mm-memory-failure-send-sigbus-in-the-event-of-thp-split-fail.patch