sched_ext: Wait for SCX_OPSS_DISPATCHING before moving tasks off DSQs

Overview

In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Wait for SCX_OPSS_DISPATCHING before moving tasks off DSQs

A task can be found on a non-local DSQ while the CPU which dispatched it is still running ops.dequeue() and hasn't cleared SCX_OPSS_DISPATCHING. The DSQ consume and move paths don't wait for the dispatch to finish and can operate on the task concurrently with the dispatcher.

Call scx_wait_dispatching() in scx_move_local_task_to_local_dsq(), unlink_dsq_and_switch_rq_lock() and move_task_between_dsqs() before they operate on the task. In scx_move_local_task_to_local_dsq(), wait before scx_resolve_local_dsq() as it may update p->scx.flags.

Affected

• Linux >= ebf1ccff79c43f860cbd2f9d6cfab9a462d0cb2d < cc2839946328c1618b3870d521b32bb9483d49d0
• Linux >= ebf1ccff79c43f860cbd2f9d6cfab9a462d0cb2d < 2935062be77113c1c4565ca9d0c72180449aafee
• Linux 7.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.