Re: netpoll trapped question

[Matt Mackall <mpm@selenic.com>]

On Tue, Sep 07, 2004 at 01:10:00PM -0400, Jeff Moyer wrote:
> ==> Regarding Re: netpoll trapped question; Matt Mackall <mpm@selenic.com> adds:
> 
> mpm> On Tue, Sep 07, 2004 at 12:53:17PM -0400, Jeff Moyer wrote: A random
> mpm> lock private to a given driver, for instance one taken on entry to the
> mpm> IRQ handler. If said driver tries to do a printk inside that lock and
> mpm> we recursively call the handler in netconsole, we're in trouble.
> mpm> These are the issues that will have to be cleaned up in individual
> mpm> drivers. So far, I haven't seen any reports, but I'm pretty sure such
> mpm> cases exist. I suppose it's also possible for us to disable recursion
> mpm> in netconsole instead of at the netpoll level.
> >> Recursion in netconsole is protected by the console semaphore.
> 
> mpm> Yes, true. But we're still in trouble if we have nic irq handler ->
> mpm> take private lock -> printk -> netconsole -> nic irq handler -> take
> mpm> private lock. See?
> 
> Okay, so that one has to be addressed on a per-driver basis.  There's no
> way for us to detect that situation.  And how do drivers address this?
> Simply don't printk inside the lock?  I think that's reasonable.

That or drop the lock where possible.

-- 
Mathematics is the supreme nostalgia of our time.