[jgoyvaerts]

Fixes a hard hang in the misfit rotation from #690 (2d24fbce39a3).

misfit_rotate_work() checks that the misfit task p is still on src_cpu, then reads the bigger CPUs' rq->curr without taking their locks. If load balancing pulls p onto a bigger CPU in that window, the scan can return p itself. migrate_swap(p, p) then runs migrate_swap_stop(), which takes p->pi_lock twice through guard(double_raw_spinlock) with IRQs off. That CPU never comes back, and the other CPU sits in multi_cpu_stop().

The fix skips p during the scan, which is how task_numa_compare() already handles the same case (cur == env->p).

Seen on the J616s (M4 Pro)

The machine hung hard with every core busy (a FEX build next to a game under emulation):

• CPU 5 stopped answering IPIs and the NMI backtrace.
• RCU expedited grace periods stalled.
• The misfit_rotate_mutex owner was stuck in stop_two_cpus().

It needed a hard reset. Setting NO_MISFIT_ROTATE in /sys/kernel/debug/sched/features avoids the hang until this fix is in.

Testing

• This commit, on an otherwise identical kernel/sched, has run on our daily J616s kernel since 2026-11-03 21:27 with MISFIT_ROTATE on, through the same all-core loads (game, FEX builds, kernel builds). No hang or RCU stall since.
• checkpatch is clean.

I have no deterministic reproducer: the window is a lockless read racing load balancing.

🤖 Generated with Claude Code

[RyanTheTide]

Merge train (MTL, 06/11). Gates passed on test tree 0412501 (integration/aurora 2661d71 + this batch):

• Signed-off-by from the author on every commit. Adversarial review done.
• W=1 on the touched objects: 0 new warnings. KUnit: drm/apple 112/113 (1 skip), hid 19/19, SEP 158/163 (the 4 known apple_sep_host_store failures, profile tests all pass). dt_binding_check clean. apple-dcp host selftests 86/86, run-host-tests at base parity (with Merge train: G17 hang confinement (#928) plus its host-test fixture #989's fixture).
• Regression boots of 7.3.0-aurora-mtl1106a, compared with the fleet16/fleet17 rows: M2, M1 Pro, J700 and J616s all clean (0 err-level lines, 0 AVCs, displays, Wi-Fi, BT, Touch ID, camera, speakers at minimal volume with speakerguardd, s2idle, perf at parity).