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Michael Ellerman authored
In smp_cpus_done() we need to call smp_ops->setup_cpu() for the boot CPU, which means it has to run *on* the boot CPU. In the past we ensured it ran on the boot CPU by changing the CPU affinity mask of current directly. That was removed in commit 6d11b87d ("powerpc/smp: Replace open coded task affinity logic"), and replaced with a work queue call. Unfortunately using a work queue leads to a lockdep warning, now that the CPU hotplug lock is a regular semaphore: ====================================================== WARNING: possible circular locking dependency detected ... kworker/0:1/971 is trying to acquire lock: (cpu_hotplug_lock.rw_sem){++++++}, at: [<c000000000100974>] apply_workqueue_attrs+0x34/0xa0 but task is already holding lock: ((&wfc.work)){+.+.+.}, at: [<c0000000000fdb2c>] process_one_work+0x25c/0x800 ... CPU0 CPU1 ---- ---- lock((&wfc.work)); lock(cpu_hotplug_lock.rw_sem); lock((&wfc.work)); lock(cpu_hotplug_lock.rw_sem); Although the deadlock can't happen in practice, because smp_cpus_done() only runs in early boot before CPU hotplug is allowed, lockdep can't tell that. Luckily in commit 8fb12156 ("init: Pin init task to the boot CPU, initially") tglx changed the generic code to pin init to the boot CPU to begin with. The unpinning of init from the boot CPU happens in sched_init_smp(), which is called after smp_cpus_done(). So smp_cpus_done() is always called on the boot CPU, which means we don't need the work queue call at all - and the lockdep warning goes away. Signed-off-by:
Michael Ellerman <mpe@ellerman.id.au> Reviewed-by:
Thomas Gleixner <tglx@linutronix.de>
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