When multiple patch modules patch the same function, there's no need to
patch all the intermediate functions. Just hook them all into the
original function and use the ftrace handler to find the newest one.
Also use a mutex in the register/unregister functions to protect changes
to kpatch_num_registered, kpatch_func_hash and calls to the ftrace
functions by other register/unregister invocations.
Use a mutex in the register/unregister functions to protect changes to
kpatch_num_registered, kpatch_func_hash and calls to the ftrace
functions by other register/unregister invocations.
My apologies for the size of this commit. I combined these two features
(updating API and using a hash table) into a single commit because their
implementations are tightly coupled and I didn't want to have to add
support for the old kpatch_funcs array with the new API just for the
sake of splitting up the commit :-)
- Update the core module API to get a more clear separation between core
module and patch module. This is cleaner and will help our case for
getting the core module merged upstream into the kernel.
- Convert the old kpatch_funcs array into a hash table. This is so much
nicer performance-wise and everything-else-wise than that ugly old
array.
- Do the incremental patching in stop machine. This ensures that the
funcs hash is up to date and we don't miss anything.
- Disable preemption in the ftrace handler when accessing the func hash.
That way we don't get conflicts with the stop_machine handler updating
the hash.
Print the loading/unloading messages after they have successfully
completed. Using the KERN_NOTICE log level which corresponds to a
"normal but significant condition."
Preemption shouldn't cause a problem with determining activeness safety.
Even if a thread is preempted, it'll be on the backtrace.
We may need to disable preemption when reading the kpatch_funcs array,
but I'm removing that comment for now because the kpatch_funcs array
will soon be replaced by a much better data structure, and we'll deal
with proper synchronization then.
Long ago, the kpatch_trampoline required being written in assembler, but
that's no longer needed now that it integrates nicely with ftrace.
Move it to a C function and rename it kpatch_ftrace_handler.
Josh Poimboeuf