sched_ext: Stop resolving a disabled scheduler's programs

A scheduler's BPF programs can outlive it. A timer it armed or a tracing
program it loaded can fire after ops.exit() has run, before the programs are
unloaded, and scx_prog_sched() still resolves the program to its scheduler
through ops->priv. Harmless while kfuncs touch only lifetime-stable state,
but a hazard once a kfunc reads global state a newly loaded scheduler can
change underneath it.

Add scx_sched->dead, set right after ops.exit() and drained with
synchronize_rcu(). It follows exit() rather than preceding it so exit()'s own
kfunc calls still resolve to @sch. scx_prog_sched() returns NULL for a dead
scheduler, so every kfunc's existing !sch bail rejects it at one choke
point.

v2: Check dead in the CONFIG_EXT_SUB_SCHED=n scx_prog_sched() too. (sashiko AI)

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

0 files changed, 0 insertions, 0 deletions