commit 55ed11b181 upstream.
When scx_bpf_select_cpu_dfl()/and() kfuncs are invoked outside of
ops.select_cpu() we can't rely on @p->migration_disabled to determine if
migration is disabled for the task @p.
In fact, migration is always disabled for the current task while running
BPF code: __bpf_prog_enter() disables migration and __bpf_prog_exit()
re-enables it.
To handle this, when @p->migration_disabled == 1, check whether @p is
the current task. If so, migration was not disabled before entering the
callback, otherwise migration was disabled.
This ensures correct idle CPU selection in all cases. The behavior of
ops.select_cpu() remains unchanged, because this callback is never
invoked for the current task and migration-disabled tasks are always
excluded.
Example: without this change scx_bpf_select_cpu_and() called from
ops.enqueue() always returns -EBUSY; with this change applied, it
correctly returns idle CPUs.
Fixes: 06efc9fe0b ("sched_ext: idle: Handle migration-disabled tasks in idle selection")
Cc: stable@vger.kernel.org # v6.16+
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Changwoo Min <changwoo@igalia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
4109506b7e