Linux: sched/core: Avoid false migration warning for proxy donors

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

sched/core: Avoid false migration warning for proxy donors

Proxy execution can move a blocked donor's scheduling context to the lock owner's CPU even when the donor is migration-disabled. The donor does not execute there, and its original execution CPU remains recorded in wake_cpu.

set_task_cpu() warns unconditionally for migration-disabled tasks, so a subsequent proxy migration or the wakeup path returning the donor home triggers a false positive: moving a blocked scheduling context does not violate the migration-disabled execution context.

For example, creating a mutex owner on CPU1 and a migration-disabled waiter on CPU0 can trigger the following warning:

proxy_migrate_repro: donor blocking on CPU0 with migration disabled proxy_migrate_repro: donor moved from CPU0 to CPU1 WARNING: kernel/sched/core.c:3389 at set_task_cpu+0x1d3/0x280 ... Call Trace: try_to_wake_up+0x43f/0x780 __mutex_unlock_slowpath+0x330/0x540 owner_fn+0x9f/0xc0 [proxy_migrate_repro] ... proxy_migrate_repro: donor woke on CPU0, task_cpu=0 proxy_migrate_repro: completed

Exclude blocked proxy donors from the warning. The proxy wakeup path restores an executable placement before clearing the blocked state.