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
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boot	Kbuild updates for v5.9	2020-08-09 14:10:26 -07:00
configs	xtensa: reorganize vectors placement	2020-02-04 21:57:02 -08:00
include	local64.h: make <asm/local64.h> mandatory	2021-01-12 20:18:16 +01:00
kernel	sched/core: Initialize the idle task with preemption disabled	2021-07-14 16:55:50 +02:00
lib	xtensa: propagate the calling conventions change down into csum_partial_copy_generic()	2020-08-20 15:45:21 -04:00
mm	xtensa: fix uaccess-related livelock in do_page_fault	2021-04-07 15:00:09 +02:00
oprofile
platforms	xtensa/simdisk: remove the call to check_disk_change	2020-07-08 16:20:01 -06:00
variants
Kconfig	Merge branch 'work.set_fs' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs	2020-10-22 09:59:21 -07:00
Kconfig.debug	xtensa: make stack dump size configurable	2019-11-26 11:33:39 -08:00
Makefile	xtensa: add XIP kernel support	2019-11-26 11:33:38 -08:00