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| author | Peter Zijlstra <peterz@infradead.org> | 2026-02-18 17:33:29 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2026-02-23 11:19:19 +0100 |
| commit | 5324953c06bd929c135d9e04be391ee2c11b5a19 (patch) | |
| tree | 58bb232b3cde0656cb2acf2a65e89216296fdd85 /kernel/sched/ext.c | |
| parent | 4c652a47722f69c6f2685f05b17490ea97f643a8 (diff) | |
| download | linux-next-5324953c06bd929c135d9e04be391ee2c11b5a19.tar.gz linux-next-5324953c06bd929c135d9e04be391ee2c11b5a19.zip | |
sched/core: Fix wakeup_preempt's next_class tracking
Kernel test robot reported that
tools/testing/selftests/kvm/hardware_disable_test was failing due to
commit 704069649b5b ("sched/core: Rework sched_class::wakeup_preempt()
and rq_modified_*()")
It turns out there were two related problems that could lead to a
missed preemption:
- when hitting newidle balance from the idle thread, it would elevate
rb->next_class from &idle_sched_class to &fair_sched_class, causing
later wakeup_preempt() calls to not hit the sched_class_above()
case, and not issue resched_curr().
Notably, this modification pattern should only lower the
next_class, and never raise it. Create two new helper functions to
wrap this.
- when doing schedule_idle(), it was possible to miss (re)setting
rq->next_class to &idle_sched_class, leading to the very same
problem.
Cc: Sean Christopherson <seanjc@google.com>
Fixes: 704069649b5b ("sched/core: Rework sched_class::wakeup_preempt() and rq_modified_*()")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202602122157.4e861298-lkp@intel.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260218163329.GQ1395416@noisy.programming.kicks-ass.net
Diffstat (limited to 'kernel/sched/ext.c')
| -rw-r--r-- | kernel/sched/ext.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 62b1f3ac5630..06cc0a4aec66 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -2460,7 +2460,7 @@ do_pick_task_scx(struct rq *rq, struct rq_flags *rf, bool force_scx) /* see kick_cpus_irq_workfn() */ smp_store_release(&rq->scx.kick_sync, rq->scx.kick_sync + 1); - rq->next_class = &ext_sched_class; + rq_modified_begin(rq, &ext_sched_class); rq_unpin_lock(rq, rf); balance_one(rq, prev); @@ -2475,7 +2475,7 @@ do_pick_task_scx(struct rq *rq, struct rq_flags *rf, bool force_scx) * If @force_scx is true, always try to pick a SCHED_EXT task, * regardless of any higher-priority sched classes activity. */ - if (!force_scx && sched_class_above(rq->next_class, &ext_sched_class)) + if (!force_scx && rq_modified_above(rq, &ext_sched_class)) return RETRY_TASK; keep_prev = rq->scx.flags & SCX_RQ_BAL_KEEP; |