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Subject[PATCH] powerpc: preempt: Don't touch the idle task's preempt_count during hotplug
Date
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 <bharata@linux.ibm.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
arch/powerpc/platforms/cell/smp.c | 3 ---
arch/powerpc/platforms/pseries/smp.c | 5 +----
2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/powerpc/platforms/cell/smp.c b/arch/powerpc/platforms/cell/smp.c
index c855a0aeb49c..d7ab868aab54 100644
--- a/arch/powerpc/platforms/cell/smp.c
+++ b/arch/powerpc/platforms/cell/smp.c
@@ -78,9 +78,6 @@ static inline int smp_startup_cpu(unsigned int lcpu)

pcpu = get_hard_smp_processor_id(lcpu);

- /* Fixup atomic count: it exited inside IRQ handler. */
- task_thread_info(paca_ptrs[lcpu]->__current)->preempt_count = 0;
-
/*
* If the RTAS start-cpu token does not exist then presume the
* cpu is already spinning.
diff --git a/arch/powerpc/platforms/pseries/smp.c b/arch/powerpc/platforms/pseries/smp.c
index 096629f54576..7ebf3382816a 100644
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -105,10 +105,7 @@ static inline int smp_startup_cpu(unsigned int lcpu)
return 1;
}

- /* Fixup atomic count: it exited inside IRQ handler. */
- task_thread_info(paca_ptrs[lcpu]->__current)->preempt_count = 0;
-
- /*
+ /*
* If the RTAS start-cpu token does not exist then presume the
* cpu is already spinning.
*/
--
2.25.1
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