On Wed, 15 Nov 2017, Miroslav Benes wrote: > 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. > > Petr, I did not add you Reviewed-by tags intentionally because of the changes. > > Changes from v3: > - only TASK_INTERRUPTIBLE kthreads are woken up - Petr > - documentation - Pavel > - function naming and sysfs fix - Josh > > 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 to finish > > Documentation/ABI/testing/sysfs-kernel-livepatch | 25 +++++++++ > Documentation/livepatch/livepatch.txt | 22 +++++++- > arch/powerpc/kernel/signal.c | 6 +-- > arch/x86/entry/common.c | 6 +-- > kernel/livepatch/core.c | 60 +++++++++++++++++++++ > kernel/livepatch/transition.c | 66 ++++++++++++++++++++++++ > kernel/livepatch/transition.h | 2 + > kernel/signal.c | 4 +- This is now queued in livepatching.git#for-4.16/signal-sysfs-force. Thanks, -- Jiri Kosina SUSE Labs -- 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
