netdev - Re: [PATCH RFC] spinlock: split out debugging check from spin_lock

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Message-ID: <3142935.JcJEKt2WmH@cpaasch-mac>
Date:	Thu, 11 Apr 2013 19:51:20 +0200
From:	Christoph Paasch <christoph.paasch@...ouvain.be>
To:	Neil Horman <nhorman@...driver.com>
Cc:	g@...lslaptop.think-freely.org,
	Bart Van Assche <bvanassche@....org>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH RFC] spinlock: split out debugging check from spin_lock_mutex

On Thursday 11 April 2013 13:04:05 Neil Horman wrote:
> I dont believe the deadlock you describe can happen.  The spin_lock_mutex
> operation disables irqs on the local cpu with local_irq_save, so we won't
> loose the cpu while we're holding the spinlock.  Likewise we don't restore
> the irq flags until after we release said lock.  Once we have the mutex, if
> we're preempted by another path that goes through the netpoll_poll_dev
> path, then we hit the trylock api call.  The spinlock is either released or
> held on another cpu (read: no deadlock), and if the mutex is held, then the
> trylock simply fails.

Thanks for explaining this to me. I was looking for a local_bh_disable() - but 
local_irq_save does the job too.


Thanks,
Christoph

-- 
IP Networking Lab --- http://inl.info.ucl.ac.be
MultiPath TCP in the Linux Kernel --- http://multipath-tcp.org
UCLouvain
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