From de7cb03db05a4b460edefff266bbaead70a11634 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Tue, 11 Jul 2023 19:40:50 +0200 Subject: [PATCH] mm/memory_hotplug: document the signal_pending() check in offline_pages() 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. Note that using signal_pending() instead of fatal_signal_pending() is an anti-pattern, but slowly deprecating that behavior to eventually change it in the far future is probably not worth the effort. If this ever becomes relevant for user-space, we might want to rethink. Link: https://lkml.kernel.org/r/20230711174050.603820-1-david@redhat.com Signed-off-by: David Hildenbrand Acked-by: Michal Hocko Cc: Oscar Salvador Cc: Jonathan Corbet Signed-off-by: Andrew Morton --- Documentation/admin-guide/mm/memory-hotplug.rst | 2 +- mm/memory_hotplug.c | 5 +++++ 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index 1b02fe5807cc..bd77841041af 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -669,7 +669,7 @@ when still encountering permanently unmovable pages within ZONE_MOVABLE (-> 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 diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 3f231cf1b410..7cfd13c91568 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1843,6 +1843,11 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages, 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";