Revert "softirq: more optimization"

This reverts commit 7e30374f83924b859f73f595908cfb6272ce1af2.
Revert "kernel/timer: Optimise apply_slack() for size and speed."

This reverts commit 0f2deaa36e9b8597cadc923a041c28a1b4656503.
Revert "FIX previous commit"

This reverts commit a11607f4a603ba795d6324451761f56cc855ab87.
Revert "mm: retry page fault when blocking on disk transfer"

This reverts commit 9da0c8eaa76ab14eba60c2dae5a5f4e9c19b5978.
Revert "FIX: to allow previous commit cb21b92e9cc467e1ac3fc10023fba3f093759967"

This reverts commit c7a7fc4a2fa2a603e28849654d2e17fe06c4a61d.
Revert "introduce for_each_thread() to replace the buggy while_each_thread() …"

This reverts commit cb21b92e9cc467e1ac3fc10023fba3f093759967.