sched_ext: When calling ops.dispatch() @prev must be on the same scx_sched

The @prev parameter passed into ops.dispatch() is expected to be on the
same sched. Passing in @prev which isn't on the sched can spuriously
trigger failures that can kill the scheduler. Pass in @prev iff it's on
the same sched.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 28ac7ba3ece08ad2a316b2cd75acf272c69f631f..413d0558372f04f3a22bf0515cf2749fa276035d 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2392,9 +2392,10 @@ static bool scx_dispatch_sched(struct scx_sched *sch, struct rq *rq,
                               struct task_struct *prev)
 {
        struct scx_dsp_ctx *dspc = this_cpu_ptr(scx_dsp_ctx);
-       bool prev_on_scx = prev->sched_class == &ext_sched_class;
        int nr_loops = SCX_DSP_MAX_LOOPS;
        s32 cpu = cpu_of(rq);
+       bool prev_on_sch = (prev->sched_class == &ext_sched_class) &&
+               scx_task_on_sched(sch, prev);
 
        if (consume_global_dsq(sch, rq))
                return true;
@@ -2418,7 +2419,7 @@ static bool scx_dispatch_sched(struct scx_sched *sch, struct rq *rq,
                dspc->nr_tasks = 0;
 
                SCX_CALL_OP(sch, SCX_KF_DISPATCH, dispatch, rq, cpu,
-                           prev_on_scx ? prev : NULL);
+                           prev_on_sch ? prev : NULL);
 
                flush_dispatch_buf(sch, rq);