Valentin Schneider 3c51d82d0b sched/core: Initialize the idle task with preemption disabled ... [ Upstream commit f1a0a376ca0c4ef1fc3d24e3e502acbb5b795674 ] As pointed out by commit de9b8f5dcb ("sched: Fix crash trying to dequeue/enqueue the idle thread") init_idle() can and will be invoked more than once on the same idle task. At boot time, it is invoked for the boot CPU thread by sched_init(). Then smp_init() creates the threads for all the secondary CPUs and invokes init_idle() on them. As the hotplug machinery brings the secondaries to life, it will issue calls to idle_thread_get(), which itself invokes init_idle() yet again. In this case it's invoked twice more per secondary: at _cpu_up(), and at bringup_cpu(). Given smp_init() already initializes the idle tasks for all *possible* CPUs, no further initialization should be required. Now, removing init_idle() from idle_thread_get() exposes some interesting expectations with regards to the idle task's preempt_count: the secondary startup always issues a preempt_disable(), requiring some reset of the preempt count to 0 between hot-unplug and hotplug, which is currently served by idle_thread_get() -> idle_init(). Given the idle task is supposed to have preemption disabled once and never see it re-enabled, it seems that what we actually want is to initialize its preempt_count to PREEMPT_DISABLED and leave it there. Do that, and remove init_idle() from idle_thread_get(). Secondary startups were patched via coccinelle: @begone@ @@ -preempt_disable(); ... cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Link: https://lore.kernel.org/r/20210512094636.2958515-1-valentin.schneider@arm.com Signed-off-by: Sasha Levin <sashal@kernel.org>		2021-07-14 16:55:50 +02:00
..
boot	.gitignore: add SPDX License Identifier	2020-03-25 11:50:48 +01:00
configs	scsi: sr: remove references to BLK_DEV_SR_VENDOR, leave it enabled	2020-02-24 14:59:01 -05:00
crypto	crypto: sparc - rename sha256 to sha256_alg	2020-07-16 21:49:04 +10:00
include	sparc64: Use arch_validate_flags() to validate ADI flag	2021-03-17 17:06:24 +01:00
kernel	sched/core: Initialize the idle task with preemption disabled	2021-07-14 16:55:50 +02:00
lib	sparc32: fix a user-triggerable oops in clear_user()	2021-03-04 11:38:43 +01:00
math-emu	treewide: Use fallthrough pseudo-keyword	2020-08-23 17:36:59 -05:00
mm	sparc32: Limit memblock allocation to low memory	2021-03-17 17:06:24 +01:00
net	treewide: Use fallthrough pseudo-keyword	2020-08-23 17:36:59 -05:00
oprofile
power
prom
vdso	treewide: remove DISABLE_LTO	2020-10-21 00:28:53 +09:00
Kbuild
Kconfig	sparc64: only select COMPAT_BINFMT_ELF if BINFMT_ELF is set	2021-03-04 11:38:10 +01:00
Kconfig.debug
Makefile