linux-kernel - [PATCH v2 1/5] mm/memory-failure: try to send SIGBUS even if unmap failed

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Date: Fri, 10 May 2024 00:25:58 -0600
From: Jane Chu <jane.chu@...cle.com>
To: linmiaohe@...wei.com, nao.horiguchi@...il.com, akpm@...ux-foundation.org,
        osalvador@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/5] mm/memory-failure: try to send SIGBUS even if unmap failed

For years when it comes down to kill a process due to hwpoison,
a SIGBUS is delivered only if unmap has been successful.
Otherwise, a SIGKILL is delivered. And the reason for that is
to prevent the involved process from accessing the hwpoisoned
page again.

Since then a lot has changed, a hwpoisoned page is marked and
upon being re-accessed, the memory-failure handler invokes
kill_accessing_process() to kill the process immediately.
So let's take out the '!unmap_success' factor and try to deliver
SIGBUS if possible.

Signed-off-by: Jane Chu <jane.chu@...cle.com>
Reviewed-by: Oscar Salvador <osalvador@...e.de>
---
 mm/memory-failure.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 16ada4fb02b7..739311e121af 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -514,22 +514,15 @@ void add_to_kill_ksm(struct task_struct *tsk, struct page *p,
  *
  * Only do anything when FORCEKILL is set, otherwise just free the
  * list (this is used for clean pages which do not need killing)
- * Also when FAIL is set do a force kill because something went
- * wrong earlier.
  */
-static void kill_procs(struct list_head *to_kill, int forcekill, bool fail,
+static void kill_procs(struct list_head *to_kill, int forcekill,
 		unsigned long pfn, int flags)
 {
 	struct to_kill *tk, *next;
 
 	list_for_each_entry_safe(tk, next, to_kill, nd) {
 		if (forcekill) {
-			/*
-			 * In case something went wrong with munmapping
-			 * make sure the process doesn't catch the
-			 * signal and then access the memory. Just kill it.
-			 */
-			if (fail || tk->addr == -EFAULT) {
+			if (tk->addr == -EFAULT) {
 				pr_err("%#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
 				       pfn, tk->tsk->comm, tk->tsk->pid);
 				do_send_sig_info(SIGKILL, SEND_SIG_PRIV,
@@ -1660,7 +1653,7 @@ static bool hwpoison_user_mappings(struct folio *folio, struct page *p,
 	 */
 	forcekill = folio_test_dirty(folio) || (flags & MF_MUST_KILL) ||
 		    !unmap_success;
-	kill_procs(&tokill, forcekill, !unmap_success, pfn, flags);
+	kill_procs(&tokill, forcekill, pfn, flags);
 
 	return unmap_success;
 }
@@ -1724,7 +1717,7 @@ static void unmap_and_kill(struct list_head *to_kill, unsigned long pfn,
 		unmap_mapping_range(mapping, start, size, 0);
 	}
 
-	kill_procs(to_kill, flags & MF_MUST_KILL, false, pfn, flags);
+	kill_procs(to_kill, flags & MF_MUST_KILL, pfn, flags);
 }
 
 /*
-- 
2.39.3