From: Tejun Heo Date: Fri, 10 Apr 2026 17:54:06 +0000 (-1000) Subject: sched_ext: Warn on task-based SCX op recursion X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e719e17d99aaf3922dbc15ae3ac3bb62fac32bad;p=thirdparty%2Fkernel%2Flinux.git sched_ext: Warn on task-based SCX op recursion The kf_tasks[] design assumes task-based SCX ops don't nest - if they did, kf_tasks[0] would get clobbered. The old scx_kf_allow() WARN_ONCE caught invalid nesting via kf_mask, but that machinery is gone now. Add a WARN_ON_ONCE(current->scx.kf_tasks[0]) at the top of each SCX_CALL_OP_TASK*() macro. Checking kf_tasks[0] alone is sufficient: all three variants (SCX_CALL_OP_TASK, SCX_CALL_OP_TASK_RET, SCX_CALL_OP_2TASKS_RET) write to kf_tasks[0], so a non-NULL value at entry to any of the three means re-entry from somewhere in the family. Signed-off-by: Tejun Heo Acked-by: Andrea Righi --- diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 40421698c9e3..b8dbae251fd5 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -502,10 +502,13 @@ do { \ * held by try_to_wake_up() with rq tracking via scx_rq.in_select_cpu. So if * kf_tasks[] is set, @p's scheduler-protected fields are stable. * - * These macros only work for non-nesting ops since kf_tasks[] is not stacked. + * kf_tasks[] can not stack, so task-based SCX ops must not nest. The + * WARN_ON_ONCE() in each macro catches a re-entry of any of the three variants + * while a previous one is still in progress. */ #define SCX_CALL_OP_TASK(sch, op, rq, task, args...) \ do { \ + WARN_ON_ONCE(current->scx.kf_tasks[0]); \ current->scx.kf_tasks[0] = task; \ SCX_CALL_OP((sch), op, rq, task, ##args); \ current->scx.kf_tasks[0] = NULL; \ @@ -514,6 +517,7 @@ do { \ #define SCX_CALL_OP_TASK_RET(sch, op, rq, task, args...) \ ({ \ __typeof__((sch)->ops.op(task, ##args)) __ret; \ + WARN_ON_ONCE(current->scx.kf_tasks[0]); \ current->scx.kf_tasks[0] = task; \ __ret = SCX_CALL_OP_RET((sch), op, rq, task, ##args); \ current->scx.kf_tasks[0] = NULL; \ @@ -523,6 +527,7 @@ do { \ #define SCX_CALL_OP_2TASKS_RET(sch, op, rq, task0, task1, args...) \ ({ \ __typeof__((sch)->ops.op(task0, task1, ##args)) __ret; \ + WARN_ON_ONCE(current->scx.kf_tasks[0]); \ current->scx.kf_tasks[0] = task0; \ current->scx.kf_tasks[1] = task1; \ __ret = SCX_CALL_OP_RET((sch), op, rq, task0, task1, ##args); \