Re: Followup to netpoll issues

[Francois Romieu <romieu@xxxxxxxxxxxxx>]

Matt Mackall <mpm@xxxxxxxxxxx> :
[...]
> > Sorry if I was not clear: "from anywhere" meant printk issued from
> > any part of the kernel which can interrupt the xmit_locked section
> > of a qdisc_run(), i.e. printk from irq handlers. 
> 
> Hrmm. Yes, that's uglier than I realized.
> 
> Perhaps there's a way to use the existing IRQ handler reentrancy
> avoidance to detect that we might be about to recurse on a lock.

It would help if qdisc_restart() disabled irq until xmit_lock_owner
is set (an extra memory barrier would be required btw). 

I'd say to go with in_irq() + try_lock() but one could object that
try_lock() leaves a window where a late thread could steal the
lock.

--
Ueimor