Commit e719e17d authored by Tejun Heo's avatar Tejun Heo
Browse files

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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarAndrea Righi <arighi@nvidia.com>
parent 979a98b6

kernel/sched/ext.c

+6 −1
Original line number Diff line number Diff line
@@ -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);		\