Linux kernel: What process does schedule() run in?

Question

When you call a system call such as fork in process X, the kernel is said to be executing in process context. So, fork can be said to be running in pro

Answer 1

It really depends upon where the schedule() call is made from; schedule() can be called both from process context or from a work queue. The work queues are kernel-scheduled threads:

# ps auxw | grep worker
root      1378  0.0  0.0      0     0 ?        S    20:45   0:00 [kworker/1:0]
root      1382  0.0  0.0      0     0 ?        S    20:45   0:00 [kworker/2:0]
root      1384  0.0  0.0      0     0 ?        S    20:45   0:00 [kworker/3:1]
...

The [..] signifies that the processes do not execute in userspace.

The worker_thread() function calls schedule() after handling a work item but before starting all over again.

schedule() can also be called on behalf of a process, either by a driver or by signal handling code, or filesystem internals, or myriad other options.