On 02.10.2020 14:53, Miroslav Benes wrote:
The old function will continue running, right?
Correct. It will, however, call new functions.
Ah, I see.
So, I guess, our best bet would be to rewrite the thread function so that it
contains just the event loop and calls other non-inline functions to actually
process the requests. And, perhaps, - place klp_update_patch_state() before
schedule().
Yes, that might be the way. klp_update_patch_state() might not be even
needed. If the callees are live patched, the kthread would be migrated
thanks to stack checking once a task leaves the callee.
You mean, the task runs the callee, then goes to schedule(), then, while
it waits, livepatch core checks its stack, sees no target functions
there and switches patch_state?
This will not help with this particular kernel version but could make it
possible to live-patch the request-processing functions in the future kernel
versions. The main thread function will remain unpatchable but it will call
the patched functions once we switch the patch_state for the thread.
Yes. The only issue is if the intended fix changes the semantics which is
incompatible between old and new functions (livepatch consistency model is
LEAVE_PATCHED_SET, SWITCH_THREAD, see
https://lore.kernel.org/lkml/20141107140458.GA21774@xxxxxxx/ for the
explanation if interested).
Yes, I have read that.
In our case, the fix only adds a kind of lock/unlock around the part of
the function processing actual requests. The implementation is more
complex, but, essentially, it is lock + unlock. The code not touched by
the patch already handles such locking OK, so it can work both with old
and the new versions of patched functions. And - even if some threads
use the old functions and some - the new ones. So, I guess, it should be
fine.
Regards
Miroslav
.
Thanks!
Evgenii
