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sched: Fix smp_call_function_single_async() usage for ILB

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The recent commit: 90b5363acd ("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.

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: 90b5363acd ("sched: Clean up scheduler_ipi()")
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Cc: mgorman@techsingularity.net
Link: https://lore.kernel.org/r/20200526161907.778543557@infradead.org
This commit is contained in:
Peter Zijlstra
2020-05-26 18:10:58 +02:00
committed by Ingo Molnar
parent 58ef57b16d
commit 19a1f5ec69
3 changed files with 20 additions and 37 deletions
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1
kernel/sched/sched.h
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@@ -951,6 +951,7 @@ struct rq {
struct callback_head *balance_callback;
unsigned char nohz_idle_balance;
unsigned char idle_balance;
unsigned long misfit_task_load;