+ mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages.patch added to mm-unstable branch

+ mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages.patch added to mm-unstable branch

[Andrew Morton]

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@redhat.com>
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@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@redhat.com are

mm-memory_hotplug-document-the-signal_pending-check-in-offline_pages.patch