Messages in this thread | | | Date | Mon, 22 Jun 2020 11:41:26 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/6] sched: Fix ttwu_queue_cond() |
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On Mon, Jun 22, 2020 at 10:11:22AM +0100, Mel Gorman wrote: > On Mon, Jun 15, 2020 at 02:56:55PM +0200, Peter Zijlstra wrote: > > Where the condition: > > > > !cpus_share_cache(smp_processor_id(), cpu) > > > > already implies 'cpu != smp_processor_id()', because a CPU always > > shares cache with itself, the secondary condition added in commit: > > > > 2ebb17717550 ("sched/core: Offload wakee task activation if it the wakee is descheduling") > > > > voids that implication, resulting in attempting to do local wake-ups > > through the queue mechanism. > > > > Fixes: 2ebb17717550 ("sched/core: Offload wakee task activation if it the wakee is descheduling") > > Reported-by: Paul E. McKenney <paulmck@kernel.org> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > Tested-by: Paul E. McKenney <paulmck@kernel.org> > > Yep, I mistakenly though this would be covered by the self-wakeup check > early in try_to_wake_up() but it is not
It is, one should not be able to observe 'p->on_cpu && task_cpu(cpu) == smp_processor_id()); I've since found the actual problem, find here:
https://lkml.kernel.org/r/20200620184622.GA19696@paulmck-ThinkPad-P72
I'm currently polishing the changelog a little, and will shortly post a new version of that.
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