Commit de7cb03d authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

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: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent d0366880

Documentation/admin-guide/mm/memory-hotplug.rst

+1 −1
Original line number Diff line number Diff line
@@ -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

mm/memory_hotplug.c

+5 −0
Original line number Diff line number Diff line
@@ -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";