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-rw-r--r--Documentation/livepatch/livepatch.txt18
1 files changed, 16 insertions, 2 deletions
diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index 9bcdef277a36..896ba8941702 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -183,6 +183,20 @@ tasks. No proper signal is actually delivered (there is no data in signal
pending structures). Tasks are interrupted or woken up, and forced to change
their patched state.
+Administrator can also affect a transition through
+/sys/kernel/livepatch/<patch>/force attribute. Writing 1 there clears
+TIF_PATCH_PENDING flag of all tasks and thus forces the tasks to the patched
+state. Important note! The force attribute is intended for cases when the
+transition gets stuck for a long time because of a blocking task. Administrator
+is expected to collect all necessary data (namely stack traces of such blocking
+tasks) and request a clearance from a patch distributor to force the transition.
+Unauthorized usage may cause harm to the system. It depends on the nature of the
+patch, which functions are (un)patched, and which functions the blocking tasks
+are sleeping in (/proc/<pid>/stack may help here). Removal (rmmod) of patch
+modules is permanently disabled when the force feature is used. It cannot be
+guaranteed there is no task sleeping in such module. It implies unbounded
+reference count if a patch module is disabled and enabled in a loop.
+
3.1 Adding consistency model support to new architectures
---------------------------------------------------------
@@ -439,8 +453,8 @@ Information about the registered patches can be found under
/sys/kernel/livepatch. The patches could be enabled and disabled
by writing there.
-/sys/kernel/livepatch/<patch>/signal attribute allows administrator to affect a
-patching operation.
+/sys/kernel/livepatch/<patch>/signal and /sys/kernel/livepatch/<patch>/force
+attributes allow administrator to affect a patching operation.
See Documentation/ABI/testing/sysfs-kernel-livepatch for more details.