Commit 96611c26 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched: Improve wake_up_all_idle_cpus() take #2 



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: 8850cb66 ("sched: Simplify wake_up_*idle*()")
Reported-by: default avatar <syzbot+d5b23b18d2f4feae8a67@syzkaller.appspotmail.com>
Reported-by: default avatarPavel Machek <pavel@ucw.cz>
Reported-by: default avatarQian Cai <quic_qiancai@quicinc.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarQian Cai <quic_qiancai@quicinc.com>
parent 09089db7

kernel/smp.c

+5 −7
Original line number Diff line number Diff line
@@ -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;



	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);