Currently, livepatch gradually migrate the system from an unpatched to a patched state (or vice versa). Each task drops its TIF_PATCH_PENDING itself when crossing the kernel/user space boundary or it is cleared using the stack checking approach. If there is a task which sleeps on a patched function, the whole transition can get stuck indefinitely. Livepatch has means which can be used in these cases. The transition can be cancelled and/or immediate flag may be used for the live patch. On the other hand it might be useful to poke the system a little bit and help the transition to finish by doing so. That is what the fake signal can be used for. A task sleeping/waiting in the kernel gets TIF_SIGPENDING set, it handles it and during that its TIF_PATCH_PENDING is cleared. Kthreads are only woken up, they do not handle signals suitably. Still, there are cases which neither fake signal can solve. A task can sleep uninterruptedly without reacting to signals at all. Even then, it may be safe to clear the task's TIF_PATCH_PENDING. As a last resort, admin may force such clearing for all tasks in the system with this patch set. We use the fake signal in SLES for a long time. Moreover, we don't have a stack checking there, so we rely on the fake signal a lot. We send it automatically and periodically. Changes from v2: - two sysfs attributes instead of one - Petr, Josh - better documentation about force usage - Pavel - small changes here and there Changes from v1: - better wording, typos, comments, documentation - Libor, Josh - symbolic names in sysfs instead of numbers - Libor - exit_to_usermode_loop(), call klp_update_patch_state() before do_signal() - Oleg - better names - Josh - mutex and WARN_ON_ONCE not added to klp_force_transitions() - Petr, Josh - handle idle tasks in klp_force_transitions() too - Josh Miroslav Benes (2): livepatch: send a fake signal to all blocking tasks livepatch: force transition process to finish Documentation/ABI/testing/sysfs-kernel-livepatch | 19 +++++++ Documentation/livepatch/livepatch.txt | 21 ++++++++ arch/powerpc/kernel/signal.c | 6 +-- arch/x86/entry/common.c | 6 +-- kernel/livepatch/core.c | 54 ++++++++++++++++++++ kernel/livepatch/transition.c | 65 ++++++++++++++++++++++++ kernel/livepatch/transition.h | 2 + kernel/signal.c | 4 +- 8 files changed, 170 insertions(+), 7 deletions(-) -- 2.14.3 -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
