Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [RFC][PATCH 1/7] sched: Fix smp_call_function_single_async() usage for ILB | Date | Fri, 29 May 2020 16:26:04 +0100 |
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On 26/05/20 17:10, Peter Zijlstra wrote: > The recent commit: 90b5363acd47 ("sched: Clean up scheduler_ipi()") > got smp_call_function_single_async() subtly wrong. Even though it will > return -EBUSY when trying to re-use a csd, that condition is not > atomic and still requires external serialization. > > The change in kick_ilb() got this wrong. > > While on first reading kick_ilb() has an atomic test-and-set that > appears to serialize the use, the matching 'release' is not in the > right place to actually guarantee this serialization. >
I got confused the first time I read through that, and had the same thoughts as Vincent; reading Frederic's reply and the thread helped. Could we mention the tick softirq vs ilb kick race thing in the changelog?
Otherwise the change looks okay, I couldn't convince myself there were more gaps left to fill.
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> Rework the nohz_idle_balance() trigger so that the release is in the > IPI callback and thus guarantees the required serialization for the > CSD. > > Fixes: 90b5363acd47 ("sched: Clean up scheduler_ipi()") > Reported-by: Qian Cai <cai@lca.pw> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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