Messages in this thread |  | | | Subject | Re: [PATCH] generic-ipi: fix deadlock in __smp_call_function_single | | From | Peter Zijlstra <> | | Date | Tue, 14 Sep 2010 10:03:47 +0200 |
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On Mon, 2010-09-13 at 11:02 -0700, Suresh Siddha wrote: > On Sat, 2010-09-11 at 09:42 -0700, Venkatesh Pallipadi wrote: > > Also, as we don't have rq lock around this point, it seems possible > > that the CPU that was busy and wants to kick idle load balance on > > remote CPU, could have become idle and nominated itself as idle load > > balancer. > > A busy cpu (currently running something -- one task on the rq atleast) > can't become idle in the middle of trigger_load_balance(). > > What might be happening is similar what you said but the opposite of it. > > cpu-x is idle which is also ilb_cpu > got a scheduler tick during idle > and the nohz_kick_needed() in trigger_load_balance() checks for > rq_x->nr_running which might not be zero (because of someone waking a > task on this rq etc) and this leads to the situation of the cpu-x > sending a kick to itself.
So what patches are we going to merge?
I share Heiko's opinion on that its somewhat surprising to have __smp_call_function_single() differ in this detail from smp_call_function_single() and think that merging his patch would be good in that respect. But Andrew seemed to have reservations.
We can also merge either my or Suresh's patch (which I think makes sense, but is kinda subtle) to avoid the needless self kick.
Hmm?
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