On Fri, 15 Oct 2021 12:39:02 -0500, Nathan Lynch wrote:

With PREEMPT_COUNT=y, when a CPU is offlined and then onlined again, we
get:

BUG: scheduling while atomic: swapper/1/0/0x00000000
no locks held by swapper/1/0.
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.15.0-rc2+ #100
Call Trace:
 dump_stack_lvl+0xac/0x108
 __schedule_bug+0xac/0xe0
 __schedule+0xcf8/0x10d0
 schedule_idle+0x3c/0x70
 do_idle+0x2d8/0x4a0
 cpu_startup_entry+0x38/0x40
 start_secondary+0x2ec/0x3a0
 start_secondary_prolog+0x10/0x14

[...]

Applied to powerpc/fixes.

[1/1] powerpc/smp: do not decrement idle task preempt count in CPU offline
      https://git.kernel.org/powerpc/c/787252a10d9422f3058df9a4821f389e5326c440

cheers