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sched/ext: convert scx_tasks_lock to raw spinlock

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Update scx_task_locks so that it's safe to lock/unlock in a
non-sleepable context in PREEMPT_RT kernels. scx_task_locks is
(non-raw) spinlock used to protect the list of tasks under SCX.
This list is updated during from finish_task_switch(), which
cannot sleep. Regular spinlocks can be locked in such a context
in non-RT kernels, but are sleepable under when CONFIG_PREEMPT_RT=y.

Convert scx_task_locks into a raw spinlock, which is not sleepable
even on RT kernels.

Sample backtrace:

<TASK>
dump_stack_lvl+0x83/0xa0
__might_resched+0x14a/0x200
rt_spin_lock+0x61/0x1c0
? sched_ext_dead+0x2d/0xf0
? lock_release+0xc6/0x280
sched_ext_dead+0x2d/0xf0
? srso_alias_return_thunk+0x5/0xfbef5
finish_task_switch.isra.0+0x254/0x360
__schedule+0x584/0x11d0
? srso_alias_return_thunk+0x5/0xfbef5
? srso_alias_return_thunk+0x5/0xfbef5
? tick_nohz_idle_exit+0x7e/0x120
schedule_idle+0x23/0x40
cpu_startup_entry+0x29/0x30
start_secondary+0xf8/0x100
common_startup_64+0x13e/0x148
</TASK>

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Emil Tsalapatis
2025-11-12 08:42:02 -10:00
committed by Tejun Heo
parent 5f02151c41
commit c87488a123
1 changed files with 8 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
kernel/sched/ext.c
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@@ -25,7 +25,7 @@ static struct scx_sched __rcu *scx_root;
* guarantee system safety. Maintain a dedicated task list which contains every
* task between its fork and eventual free.
*/
static DEFINE_SPINLOCK(scx_tasks_lock);
static DEFINE_RAW_SPINLOCK(scx_tasks_lock);
static LIST_HEAD(scx_tasks);
/* ops enable/disable */
@@ -476,7 +476,7 @@ static void scx_task_iter_start(struct scx_task_iter *iter)
BUILD_BUG_ON(__SCX_DSQ_ITER_ALL_FLAGS &
((1U << __SCX_DSQ_LNODE_PRIV_SHIFT) - 1));
spin_lock_irq(&scx_tasks_lock);
raw_spin_lock_irq(&scx_tasks_lock);
iter->cursor = (struct sched_ext_entity){ .flags = SCX_TASK_CURSOR };
list_add(&iter->cursor.tasks_node, &scx_tasks);
@@ -507,14 +507,14 @@ static void scx_task_iter_unlock(struct scx_task_iter *iter)
__scx_task_iter_rq_unlock(iter);
if (iter->list_locked) {
iter->list_locked = false;
spin_unlock_irq(&scx_tasks_lock);
raw_spin_unlock_irq(&scx_tasks_lock);
}
}
static void __scx_task_iter_maybe_relock(struct scx_task_iter *iter)
{
if (!iter->list_locked) {
spin_lock_irq(&scx_tasks_lock);
raw_spin_lock_irq(&scx_tasks_lock);
iter->list_locked = true;
}
}
@@ -2940,9 +2940,9 @@ void scx_post_fork(struct task_struct *p)
}
}
spin_lock_irq(&scx_tasks_lock);
raw_spin_lock_irq(&scx_tasks_lock);
list_add_tail(&p->scx.tasks_node, &scx_tasks);
spin_unlock_irq(&scx_tasks_lock);
raw_spin_unlock_irq(&scx_tasks_lock);
percpu_up_read(&scx_fork_rwsem);
}
@@ -2966,9 +2966,9 @@ void sched_ext_free(struct task_struct *p)
{
unsigned long flags;
spin_lock_irqsave(&scx_tasks_lock, flags);
raw_spin_lock_irqsave(&scx_tasks_lock, flags);
list_del_init(&p->scx.tasks_node);
spin_unlock_irqrestore(&scx_tasks_lock, flags);
raw_spin_unlock_irqrestore(&scx_tasks_lock, flags);
/*
* @p is off scx_tasks and wholly ours. scx_enable()'s READY -> ENABLED