livepatch: Send a fake signal periodically

An administrator may send a fake signal to all remaining blocking tasks
of a running transition by writing to
/sys/kernel/livepatch/<patch>/signal attribute. Let's do it
automatically after 15 seconds. The timeout is chosen deliberately. It
gives the tasks enough time to transition themselves.

Theoretically, sending it once should be more than enough. However,
every task must get outside of a patched function to be successfully
transitioned. It could prove not to be simple and resending could be
helpful in that case.

A new workqueue job could be a cleaner solution to achieve it, but it
could also introduce deadlocks and cause more headaches with
synchronization and cancelling.

[jkosina@suse.cz: removed added newline]
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 2 insertions, 1 deletions

diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index 71d7f286ec4d..407e0f03dc99 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -163,7 +163,8 @@ patched state. This may be harmful to the system though.
 Writing 1 to the attribute sends a fake signal to all remaining blocking
 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.
+their patched state. Despite the sysfs attribute the fake signal is also sent
+every 15 seconds automatically.
 
 Administrator can also affect a transition through
 /sys/kernel/livepatch/<patch>/force attribute. Writing 1 there clears