scx_sched_hash is inserted into under scx_sched_lock (raw_spinlock_irq)
in scx_link_sched(). rhashtable's sync grow path calls get_random_u32()
and does a GFP_ATOMIC allocation; both acquire regular spinlocks, which
is unsafe under raw_spinlock_t. Set insecure_elasticity to skip the
sync grow.

v2:
- Dropped dsq_hash changes. Insertion is not under raw_spin_lock.

- Switched from no_sync_grow flag to insecure_elasticity.

Fixes: 25037af712eb ("sched_ext: Add rhashtable lookup for sub-schedulers")
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/sched/ext.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -32,6 +32,7 @@ static const struct rhashtable_params sc
 	.key_len		= sizeof_field(struct scx_sched, ops.sub_cgroup_id),
 	.key_offset		= offsetof(struct scx_sched, ops.sub_cgroup_id),
 	.head_offset		= offsetof(struct scx_sched, hash_node),
+	.insecure_elasticity	= true,	/* inserted under scx_sched_lock */
 };
 
 static struct rhashtable scx_sched_hash;

Applying the rhashtable patch and sched_ext fix to sched_ext/for-7.1-fixes.
Herbert, if this wasn't what you meant and want the rhashtable patch routed
differently, please let me know.

Thanks.

-- 
tejun