linux-kernel - Re: [PATCH rev2 1/4] dmaengine: enable mutliple clients and operations

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Message-Id: <20060731.231158.91311705.davem@davemloft.net>
Date:	Mon, 31 Jul 2006 23:11:58 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	dan.j.williams@...el.com
Cc:	linux-kernel@...r.kernel.org, neilb@...e.de,
	galak@...nel.crashing.org, christopher.leech@...el.com,
	alan@...rguk.ukuu.org.uk
Subject: Re: [PATCH rev2 1/4] dmaengine: enable mutliple clients and
 operations

Can I ask that the known bugs in the I/O AT DMA code be fixed
before we start adding new features to it?

Specifically, the lock_cpu_hotplug() call in net_dma_rebalance()
is still there and being invoked with a spinlock held.  The
spinlock is grabbed by the caller, netdev_dma_event() which
grabs the net_dma_event_lock spinlock.

You cannot invoke lock_cpu_hotplug() while holding a spinlock
because lock_cpu_hotplug(), as seen in kernel/cpu.c, takes
a semaphore which can sleep.  Sleeping while holding a spinlock
is not allowed.

This is the second time I have tried to make the Intel developers
aware of this bug.  So please fix this problem.

Thanks a lot.
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