Hello guys,
I'm new to livepatch world and now I'm a little confused with livepatch's
per-task consistency model which is introduced by [1]. I've also readed the
discussion on mailing list [2], which introduces shadow variable to handle
data layout and semantic changes. But there's still some confusion with this
per-task consistency model.
According to the model, there will be scenario where old function and new
function can co-exist, though for a single thread, it sees either all new
functions or all old functions.
I can't understand why Vojtech said that 'old func processing new data' was
impossible. Assuming a scenario where a process calls func-A to submit a
work request (inserted into a global list), and then a kthread is
responsible
for calling func-B to process all work requests in the list. What if
this process
has finished the transition (sees new func-A) while kthread still sees
the old func-B?
In this case, old func-B has to process new data. If there's some lock
semantic
changes in func-A and func-B, then old func-B has no way identifying the
shadow
variable labeled by new func-A.
Please tell me if I missed something, and any suggestions will be
appreciated. ;)
Thanks.
[1] livepatch: change to a per-task consistency model
(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.6-rc3&id=d83a7cb375eec21f04c83542395d08b2f6641da2)
[2] https://lkml.kernel.org/r/20141107140458.GA21774@xxxxxxx
