sched_ext: Queue the kick_sync wait from set_next_task_scx()

The SCX_KICK_WAIT wait is deferred to rq->scx.kick_sync_bal_cb, which a
final pick queues on the local rq. Under core scheduling, a pick that
returns a task isn't final: pick_next_task() goes on to pick the SMT
siblings, and their dispatch can release the shared rq lock with the
callback still queued. A CPU acquiring the rq lock in that window then
finds a pending balance callback and triggers the warning in
rq_pin_lock().

Fix this by queuing the callback from set_next_task_scx() on SNT_PICK
and SNT_REPICK. put_prev_set_next_task() calls it once the pick is
final, after the core-wide selection, so the rq lock can't be dropped
with the callback queued. If the CPU ends up running idle or a higher
class task, no SCX task runs there and there's nothing to wait for:
kick_sync_pending stays set and the next pick of an SCX task waits
before running it.

Also, proxy exec zaps the balance callbacks and picks again when
find_proxy_task() fails, so clear kick_sync_pending when the callback
runs rather than when it's queued.

Fixes: 415cb193bb97 ("sched_ext: Fix SCX_KICK_WAIT deadlock by deferring wait to balance callback")
Cc: stable@vger.kernel.org # v7.0+: c72945693b90: sched: Restart fair hrtick after same-task repicks
Cc: stable@vger.kernel.org # v7.0+
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

0 files changed, 0 insertions, 0 deletions