kern: cpuset: drop the lock to allocate domainsets

[kevans]

Summary

Restructure the loop a little bit to make it a little more clear how it really operates: we never allocate any domains at the beginning of the first iteration, and it will run until we've satisfied the amount we need or we encounter an error.

The lock is now taken outside of the loop to make stuff inside the loop easier to evaluate w.r.t. locking.

This fixes it to not try and allocate any domains for the freelist under the spinlock, which would have happened before if we needed any new domains.

Reported-by: [e-mail]

[markj]

Thanks. I tested this patch with syzkaller's repro for the bug, seems to be fixed.

Reported-by: [e-mail]

It'll still work if you write "Reported by:" as we normally do, i.e. without the dash.