Trace

Still requires a few fixes, but the main part is done.
Here is a report I otherwise get:

```
==================================================================
ThreadSanitizer: data-race in worker_thread

Read of size 8 by thread T4 (K4):
 [<ffffffff810ab428>] worker_thread+0x48/0x730 /kernel/workqueue.c:2104
 [<ffffffff810b500b>] kthread+0x14b/0x170 /kernel/kthread.c:207
 [<ffffffff81dc1cfc>] ret_from_fork+0x7c/0xb0 /arch/x86/kernel/entry_64.S:347
DBG: cpu = ffff88041fc15df0

Previous write of size 8 by thread T1 (K1):
 [<ffffffff810a944e>] create_worker+0x12e/0x290 /kernel/workqueue.c:1695
 [<ffffffff82311b5f>] init_workqueues+0x4b9/0x774 /kernel/workqueue.c:4861
 [<ffffffff8100032d>] do_one_initcall+0xbd/0x220 /init/main.c:794
 [<     inlined    >] kernel_init_freeable+0x1b7/0x375 do_pre_smp_initcalls /init/main.c:896
 [<ffffffff822fd707>] kernel_init_freeable+0x1b7/0x375 /init/main.c:1002
 [<ffffffff810004a6>] kernel_init+0x16/0x150 /init/main.c:938
 [<ffffffff81dc1cfc>] ret_from_fork+0x7c/0xb0 /arch/x86/kernel/entry_64.S:347
DBG: cpu = 0

DBG: addr: ffff8801ec02c740
DBG: first offset: 0, second offset: 0
DBG: first clock: 425892, second clock: 34
==================================================================
```

The write to worker->task happens before the worker task is put on the run-queue, which happens before the task is fetched from the run-queue, which happens before the write to worker->task->flags.

There must be some synchronization I miss inside the scheduler.
I'll look into it, for now I'll just remove ktsan_thr_wakeup.