On 12.07.23 08:47, Anshuman Khandual wrote:
On 7/11/23 23:10, David Hildenbrand wrote:
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.
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
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.> + */
Just curious, could 'signal type' to stop memory offline process be considered
an ABI and cannot be changed in kernel ever if required ? Just wondering if an
additional '!fatal_signal_pending()' check be introduced to warn about support
being deprecated, before finally replacing it with fatal_signal_pending().
See my reply to Michal, while that would be doable it is probably not
worth the effort, and we'd still have to stick with the existing
handling for quite a while.
Thanks!
--
Cheers,
David / dhildenb
