Re: [Xen-devel] Xen PVM: Strange lockups when running PostgreSQL load

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.10.12 at 22:52, Stefan Bader <stefan.bader@xxxxxxxxxxxxx> wrote:
> Actually I begin to suspect that it could be possible that I just overlooked 
> the
> most obvious thing. Provoking question: are we sure we are on the same page
> about the purpose of the spin_lock_flags variant of the pv lock ops 
> interface?
> 
> I begin to suspect that it really is not for giving a chance to re-enable
> interrupts. Just what it should be used for I am not clear. Anyway it seems 
> all
> other places more or less ignore the flags and map themselves back to an
> ignorant version of spinlock.
> Also I believe that the only high level function that would end up in 
> passing
> any flags, would be the spin_lock_irqsave one. And I am pretty sure that 
> this
> one will expect interrupts to stay disabled.

No - the only requirement here is that from the point on where
the lock is owned interrupt must remain disabled. Re-enabling
intermediately is quite okay (and used to be done by the
native kernel prior to the conversion to ticket locks iirc).

> So I tried below approach and that seems to be surviving the previously 
> breaking
> testcase for much longer than anything I tried before.

If that indeed fixes your problem, then (minus eventual problems
with the scope of the interrupts-enabled window) this rather
points at a bug in the users of the spinlock interfaces.

Jan


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