Messages in this thread | | | Date | Tue, 21 Oct 2014 12:10:11 +0200 | From | Thomas Petazzoni <> | Subject | Re: RCU stall in af_unix.c, should use spin_lock_irqsave? |
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Dear Eric Dumazet,
On Tue, 21 Oct 2014 03:04:34 -0700, Eric Dumazet wrote:
> > So, the question is: is this patch the correct solution (but then other > > usage of spin_lock in af_unix.c might also need fixing) ? Or is the > > network driver at fault? > > > > Thanks for your input, > > > > Thomas > > Locks in af_unix do not need to mask irqs. Ever. > > skb_queue_tail() uses an irqsave variant because its a generic function, > and _some_ skb list might be manipulated from hard irq handlers in pre > NAPI drivers. But af_unix does not have an interrupt handler that could > potentially try to lock sk_receive_queue.lock
Ok. So it's actually safe to mix spin_lock() and spin_lock_irqsave() on the same lock, if you know that this lock will never ever be taken in an interrupt context?
> mvpp2 is seriously brain damaged : on_each_cpu() cannot be used from > a bottom half handler.
That's what I thought. Back to the drawing board then, to fix mvpp2.
Do you think there is a place where we can write down those assumptions? It isn't easy to spot whether on_each_cpu() is safe to use in a bottom half or not.
Anyway, thanks a lot for your quick feedback!
Best regards,
Thomas -- Thomas Petazzoni, CTO, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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