Re: [Xen-devel] [RFC] x86/watchdog: Always disable watchdog before console_force_unlock()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.08.13 at 23:17, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> Depending on the state of the conring and serial_tx_buffer,
> console_force_unlock() can be a long running operation, usually because of
> serial_start_sync()
> 
> XenServer testing has found a reliable case where console_force_unlock() on
> one PCPU takes long enough for another PCPU to timeout due to the watchdog
> (such as waiting for a tlb flush callin).
> 
> The watchdog timeout causes the second PCPU to repeat the
> console_force_unlock(), at which point the first PCPU typically fails an
> assertion in spin_unlock_irqrestore(&port->tx_lock) (because the tx_lock has
> been unlocked behind itself).
> 
> console_force_unlock() is only on emergency paths, so one way or another the
> host is going down.  Disable the watchdog before forcing the console lock to
> help prevent having pcpus completing with each other to bring the host down.

So perhaps rather than calling watchdog_disable() before calling
console_force_unlock(), would we not better call the former first
thing from the latter?

Jan


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