From 2b6148ef2bd6d8ddc76e7873114f7769b6aa25f0 Mon Sep 17 00:00:00 2001
From: Valentin Schneider <valentin.schneider@arm.com>
Date: Wed, 7 Jul 2021 19:38:31 +0100
Subject: [PATCH] powerpc/preempt: Don't touch the idle task's preempt_count
during hotplug
commit 2c669ef6979c370f98d4b876e54f19613c81e075 upstream.
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.
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>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Bharata B Rao <bharata@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210707183831.2106509-1-valentin.schneider@arm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/platforms/cell/smp.c | 3 ---
arch/powerpc/platforms/pseries/smp.c | 3 ---
2 files changed, 6 deletions(-)
diff --git a/arch/powerpc/platforms/cell/smp.c b/arch/powerpc/platforms/cell/smp.c
index c855a0aeb49cc..d7ab868aab54a 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 096629f545769..f47429323eee9 100644
--- a/arch/powerpc/platforms/pseries/smp.c
+++ b/arch/powerpc/platforms/pseries/smp.c
@@ -105,9 +105,6 @@ 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.
--
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