On Fri, 6 Jan 2017, Josh Poimboeuf wrote: > On Fri, Jan 06, 2017 at 03:00:45PM +0100, Miroslav Benes wrote: > > > > 2. reversion of the process does not work as expected. The kernel > > crashes after the removal of the module. A task very likely slept in > > schedule and was not migrated properly. It might be because of the races > > in klp_reverse_transition() described by Petr, or might be somewhere > > else. I'll look into it. > > Hm, will be interesting to see the cause of this...
The absence of the patched schedule() on the stack was the cause. klp_try_switch_task() thus did not see it and happily migrated the task. The reason is funny. One cannot patch __schedule() (which is of interested) because of the notrace attribute. So all the callers need to be processed. I tried to make my life easier and patched only schedule(). GCC then inlined new __schedule() to the new schedule(). When I added noinline attribute to the new __schedule() everything was fine (because suddenly new schedule() was on the stack as expected). There is still one thing which I don't understand. Why __schedule() (patched or the original) is not on the stack. The actual "sleep" should happen in __switch_to_asm() which is C function now. And there is a call to __switch_to_asm() in __schedule(). __schedule() thus should be on the stack, shouldn't it? What am I missing? __switch_to_asm() pushes %rbp on the stack... Miroslav
