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Re: [Xen-devel] [PATCH]: Fix deadlock in mm_pin

On 20/11/08 10:31, "Chris Lalancette" <clalance@xxxxxxxxxx> wrote:

> it applies to the 2.6.18 tree as well; the deadlock scenario is below.
> "After running an arbitrary workload involving network traffic for some time
> (1-2 days), a xen guest running the 2.6.9-67 x86_64 xenU kernel locks up with
> both vcpu's spinning at 100%.
> The problem is due to a race between the scheduler and network interrupts.  On
> one vcpu, the scheduler takes the runqueue spinlock of the other vcpu to
> schedule a process, and attempts to lock mm_unpinned_lock.  On the other vcpu,
> another process is holding mm_unpinned_lock (because it is starting or
> exiting), and is interrupted by a network interrupt.  The network interrupt
> handler attempts to wake up the same process that the first vcpu is trying to
> schedule, and will try to get the runqueue spinlock that the first vcpu is
> already holding."

I don't believe that mm_unpinned_lock can ever be taken while a runqueue
lock is already held in 2.6.18. If you can provide a call chain then I'll
consider the patch -- but I think you'd still be screwed by the
mm->page_table_lock (also acquired in mm_pin() code, also not IRQ safe, but
less easy for you to go convert all the users of that lock).

You might have some backporting from 2.6.18 to do...

 -- Keir

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