Re: [PATCH] powerpc: preempt: Don't touch the idle task's preempt_count during hotplug

On Wed, Jul 07, 2021 at 07:38:31PM +0100, Valentin Schneider wrote:

Powerpc currently resets a CPU's idle task preempt_count to 0 before said
task starts executing the secondary startup routine (and becomes an idle
task proper).

This conflicts with commit

  f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled")

which initializes all of the idle tasks' preempt_count to PREEMPT_DISABLED
during smp_init(). Note that this was superfluous before said commit, as
back then the hotplug machinery would invoke init_idle() via
idle_thread_get(), which would have already reset the CPU's idle task's
preempt_count to PREEMPT_ENABLED.

Get rid of this preempt_count write.

Cc: Guenter Roeck <linux@roeck-us.net>
Fixes: f1a0a376ca0c ("sched/core: Initialize the idle task with preemption disabled")
Reported-by: Bharata B Rao <redacted>
Signed-off-by: Valentin Schneider <redacted>
---
 arch/powerpc/platforms/cell/smp.c    | 3 ---
 arch/powerpc/platforms/pseries/smp.c | 5 +----
 2 files changed, 1 insertion(+), 7 deletions(-)

The messages like "BUG: scheduling while atomic: swapper/1/0/0x00000000"
for each secondary CPU are no longer seen after this patch on powerpc.

Tested-by: Bharata B Rao <redacted>