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sched: Improve wake_up_all_idle_cpus() take #2

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As reported by syzbot and experienced by Pavel, using cpus_read_lock()
in wake_up_all_idle_cpus() generates lock inversion (against mmap_sem
and possibly others).

Instead, shrink the preempt disable region by iterating all CPUs and
checking the online status for each individual CPU while having
preemption disabled.

Fixes: 8850cb663b ("sched: Simplify wake_up_*idle*()")
Reported-by: syzbot+d5b23b18d2f4feae8a67@syzkaller.appspotmail.com
Reported-by: Pavel Machek <pavel@ucw.cz>
Reported-by: Qian Cai <quic_qiancai@quicinc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Qian Cai <quic_qiancai@quicinc.com>
This commit is contained in:
Peter Zijlstra 2021-10-18 16:41:05 +02:00
parent 09089db798
commit 96611c26dc
1 changed files with 5 additions and 7 deletions
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12
kernel/smp.c
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@ -1170,14 +1170,12 @@ void wake_up_all_idle_cpus(void)
{
int cpu;
cpus_read_lock();
for_each_online_cpu(cpu) {
if (cpu == raw_smp_processor_id())
continue;
wake_up_if_idle(cpu);
for_each_possible_cpu(cpu) {
preempt_disable();
if (cpu != smp_processor_id() && cpu_online(cpu))
wake_up_if_idle(cpu);
preempt_enable();
}
cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);