Re: RT and Cascade interrupts

[john cooper <john.cooper@timesys.com>]

Ingo Molnar wrote:
> * john cooper <john.cooper@timesys.com> wrote:
>>The RPC code is attempting to replicate state of
>>timer ownership for a given rpc_task via RPC_TASK_HAS_TIMER
>>in rpc_task.tk_runstate.  Besides not working
>>correctly in the case of preemptable context it is
>>a replication of state of a timer pending in the
>>cascade structure (ie: timer->base).  The fix
>>changes the RPC code to use timer->base when
>>deciding whether an outstanding timer registration
>>exists during rpc_task tear down.
>>
>>Note: this failure occurred in the 40-04 version of
>>the patch though it applies to more current versions.
>>It was seen when executing stress tests on a number
>>of PPC targets running on an NFS mounted root though
>>was not observed on a x86 target under similar
>>conditions.
> 
> 
> should this fix go upstream too?

Yes.  The RPC code is attempting to replicate existing
and easily accessible state information in a timer
structure.  The simplistic means by which it does so
fails if ksoftirqd/rpc_run_timer() runs in preemptive
context.

-john


-- 
john.cooper@timesys.com