sched_ext: Don't queue balance callbacks from a core-sched pick

Commit ff0545e0c263 ("sched_ext: Don't leave balance callbacks queued
across a pick retry") queues the deferred work as a balance callback
only when do_pick_task_scx() returns a final pick. However, under core
scheduling, a pick that returns a task isn't final either:
pick_next_task() goes on to pick the SMT siblings, and their dispatch
can release the shared rq lock with the callback still queued,
triggering the rq_pin_lock() warning.

Moreover, dispatch_core_pick() returns early when another dispatch is
in flight on the rq, and do_pick_task_scx() then consumes
%SCX_RQ_BAL_CB_PENDING set by that dispatch while it's still running.

This can be reproduced running scx_qmap -I on SMT siblings with
coresched-tagged workloads that frequently sleep, mixed with untagged
CPU-bound tasks.

Fix this by always deferring the pending work to the irq_work path from
dispatch_core_pick() under core scheduling, for both the local and the
sibling picks, and by leaving %SCX_RQ_BAL_CB_PENDING alone in
do_pick_task_scx(), so that it's handled by the dispatch that set it.
Sample the core scheduling state once at the start of the pick, since
core scheduling can get enabled while a non-core dispatch has the rq lock
released, and the follow-up work must match the dispatch path that ran.

Fixes: 4c95380701f5 ("sched/ext: Fold balance_scx() into pick_task_scx()")
Cc: stable@vger.kernel.org # v6.19+
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

0 files changed, 0 insertions, 0 deletions