patches/old/mm-memory-failure-try-to-send-sigbus-even-if-unmap-failed.patch

From: Jane Chu <jane.chu@oracle.com>
Subject: mm/memory-failure: try to send SIGBUS even if unmap failed
Date: Fri, 24 May 2024 15:53:02 -0600

Patch series "Enhance soft hwpoison handling and injection", v4.

This series is aimed at the following enhancements:

- Let one hwpoison injector, that is, madvise(MADV_HWPOISON) to behave
  more like as if a real UE occurred.  Because the other two injectors
  such as hwpoison-inject and the 'einj' on x86 can't, and it seems to me
  we need a better simulation to real UE scenario.
- For years, if the kernel is unable to unmap a hwpoisoned page, it send
  a SIGKILL instead of SIGBUS to prevent user process from potentially
  accessing the page again.  But in doing so, the user process also lose
  important information: vaddr, for recovery.  Fortunately, the kernel
  already has code to kill process re-accessing a hwpoisoned page, so
  remove the '!unmap_success' check.
- Right now, if a thp page under GUP longterm pin is hwpoisoned, and
  kernel cannot split the thp page, memory-failure simply ignores the UE
  and returns.  That's not ideal, it could deliver a SIGBUS with useful
  information for userspace recovery.


This patch (of 5):

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.

Link: https://lkml.kernel.org/r/20240524215306.2705454-1-jane.chu@oracle.com
Link: https://lkml.kernel.org/r/20240524215306.2705454-2-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 |   15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

--- a/mm/memory-failure.c~mm-memory-failure-try-to-send-sigbus-even-if-unmap-failed
+++ a/mm/memory-failure.c
@@ -514,22 +514,15 @@ void add_to_kill_ksm(struct task_struct
  *
  * 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(struc
 	 */
 	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_h
 		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);
 }
 
 /*
_