netdev - Re: [PATCH] bonding: change spinlocks and remove timers in favor of workqueues

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Date:	Thu, 30 Nov 2006 11:38:43 -0800
From:	Jay Vosburgh <fubar@...ibm.com>
To:	Andy Gospodarek <andy@...yhouse.net>
cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] bonding: change spinlocks and remove timers in favor of workqueues 


Andy Gospodarek <andy@...yhouse.net> wrote:
>The main purpose of this patch is to clean-up the bonding code so that
>several important operations are not done in the incorrect (softirq)
>context. Whenever a kernel is compiled with CONFIG_DEBUG_SPINLOCK_SLEEP
>all sorts of backtraces are spewed to the log since might_sleep will
>kindly remind us we are doing something in a atomic context when we
>probably should not.
[...]

	I'll look at the patch in detail in a bit (and I have 802.3ad
switches to test on), but on first glance, does this not still hold a
lock during failover operations in balance-alb mode?  I.e., this doesn't
change the locking model, it just moves the timers to workqueues and
relaxes the _bh locking.

	The really problematic case calls dev_set_mac_address() with a
lock held, and I don't see that this patch changes that behavior.  Do
you still get the lock warnings during link fail / recovery in
balance-alb mode?

	Also, on an CONFIG_PREEMPT kernel, it'll still get the sleep
warnings, since in_atomic() will trip __might_sleep() for any lock (if
I'm reading things correctly).

	Don't get me wrong, this (switching to workqueues, etc) needs to
be done, but I don't think this patch really resolves the underlying
problem that causes the warnings.

	Let me see if I can dust off the extensive patch that does
change the locking model; I'll see if I can bring it up to the current
git and post it.

	-J

---
	-Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
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