diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2020-05-26 18:10:58 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2020-05-28 10:54:15 +0200 |
| commit | 19a1f5ec699954d21be10f74ff71c2a7079e99ad (patch) | |
| tree | 4ec037e6193e760846705d2a9bcb9948f03187aa /kernel/sched/fair.c | |
| parent | 58ef57b16d9e91cce1c640a6fe8a21d53a85181d (diff) | |
sched: Fix smp_call_function_single_async() usage for ILB
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.
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>
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
Diffstat (limited to 'kernel/sched/fair.c')
| -rw-r--r-- | kernel/sched/fair.c | 18 |
1 files changed, 8 insertions, 10 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index dda9b194d225..2890bd54a088 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10024,6 +10024,10 @@ static void kick_ilb(unsigned int flags) if (ilb_cpu >= nr_cpu_ids) return; + /* + * Access to rq::nohz_csd is serialized by NOHZ_KICK_MASK; he who sets + * the first flag owns it; cleared by nohz_csd_func(). + */ flags = atomic_fetch_or(flags, nohz_flags(ilb_cpu)); if (flags & NOHZ_KICK_MASK) return; @@ -10371,20 +10375,14 @@ abort: */ static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { - int this_cpu = this_rq->cpu; - unsigned int flags; + unsigned int flags = this_rq->nohz_idle_balance; - if (!(atomic_read(nohz_flags(this_cpu)) & NOHZ_KICK_MASK)) + if (!flags) return false; - if (idle != CPU_IDLE) { - atomic_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu)); - return false; - } + this_rq->nohz_idle_balance = 0; - /* could be _relaxed() */ - flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu)); - if (!(flags & NOHZ_KICK_MASK)) + if (idle != CPU_IDLE) return false; _nohz_idle_balance(this_rq, flags, idle); |