Re: [PATCH RESEND -rt] mm: perform lru_add_drain_all() remotely

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

* Sebastian Andrzej Siewior | 2016-05-12 10:42:30 [+0200]:

>>diff --git a/mm/swap.c b/mm/swap.c
>>index ca194ae..84c3c21 100644
>>--- a/mm/swap.c
>>+++ b/mm/swap.c
>>@@ -821,9 +821,9 @@ void lru_add_drain_cpu(int cpu)
>> 		unsigned long flags;
>> 
>> 		/* No harm done if a racing interrupt already did this */
>>-		local_lock_irqsave(rotate_lock, flags);
>>+		local_lock_irqsave_other_cpu(rotate_lock, flags, cpu);
>> 		pagevec_move_tail(pvec);
>>-		local_unlock_irqrestore(rotate_lock, flags);
>>+		local_unlock_irqrestore_other_cpu(rotate_lock, flags, cpu);
>
>This piece might be required independently of this patch. It would be
>nice to have it in page_alloc_cpu_notify() :) I take care of this…

no, I won't :)
It looks halfway like an upstream bug. Vanila has here local_irq_save()
which always matches the local CPU except when it is invoked from
page_alloc_cpu_notify() CPU_DEAD notifier. Here it does not matter
because the CPU is gone and won't take the locks anymore.
Unless, we start taking them cross-CPU which is only possible with this
patch.

Sebastian
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