The patch titled
Subject: mm/memory_hotplug: document the signal_pending() check in offline_pages()
has been added to the -mm mm-unstable branch. Its filename is
mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/memory_hotplug: document the signal_pending() check in offline_pages()
Date: Tue, 11 Jul 2023 19:40:50 +0200
Let's update the documentation that any signal is sufficient, and add a
comment that not only checking for fatal signals is historical baggage:
changing it now could break existing user space. although unlikely.
For example, when an app provides a custom SIGALRM handler and triggers
memory offlining, the timeout cmd would no longer stop memory offlining,
because SIGALRM would no longer be considered a fatal signal.
Link: https://lkml.kernel.org/r/20230711174050.603820-1-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/mm/memory-hotplug.rst | 2 +-
mm/memory_hotplug.c | 5 +++++
2 files changed, 6 insertions(+), 1 deletion(-)
--- a/Documentation/admin-guide/mm/memory-hotplug.rst~mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages
+++ a/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -669,7 +669,7 @@ when still encountering permanently unmo
(-> BUG), memory offlining will keep retrying until it eventually succeeds.
When offlining is triggered from user space, the offlining context can be
-terminated by sending a fatal signal. A timeout based offlining can easily be
+terminated by sending a signal. A timeout based offlining can easily be
implemented via::
% timeout $TIMEOUT offline_block | failure_handling
--- a/mm/memory_hotplug.c~mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages
+++ a/mm/memory_hotplug.c
@@ -1843,6 +1843,11 @@ int __ref offline_pages(unsigned long st
do {
pfn = start_pfn;
do {
+ /*
+ * Historically we always checked for any signal and
+ * can't limit it to fatal signals without eventually
+ * breaking user space.
+ */
if (signal_pending(current)) {
ret = -EINTR;
reason = "signal backoff";
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages.patch
