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[Userspace LL] schedule: zephyr_ll: grant LL thread access to per-task semaphores #11080

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[Userspace LL] schedule: zephyr_ll: grant LL thread access to per-task semaphores #11080

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1 change: 1 addition & 0 deletions src/include/sof/schedule/ll_schedule_domain.h
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Original file line number Diff line number Diff line change
Expand Up @@ -328,6 +328,7 @@ struct ll_schedule_domain *zephyr_domain_init(int clk);
#define timer_domain_init(timer, clk) zephyr_domain_init(clk)
#ifdef CONFIG_SOF_USERSPACE_LL
struct k_thread *zephyr_domain_thread_tid(struct ll_schedule_domain *domain);
struct k_thread *zephyr_domain_thread_tid_for_core(int core);
struct k_mem_domain *zephyr_ll_mem_domain(void);
#endif /* CONFIG_SOF_USERSPACE_LL */
#ifdef CONFIG_SOF_FULL_ZEPHYR_APPLICATION
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27 changes: 27 additions & 0 deletions src/schedule/zephyr_domain.c
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Expand Up @@ -289,6 +289,14 @@ static int zephyr_domain_unregister(struct ll_schedule_domain *domain,

#else /* CONFIG_SOF_USERSPACE_LL */

/*
* Kernel-owned per-core LL thread table. Populated from the privileged
* domain-thread init path and consulted by z_impl_zephyr_ll_task_sem_alloc()
* so that privileged code never has to traverse the user-accessible
* scheduler/domain objects to find the LL thread of a given core.
*/
static struct k_thread *ll_thread_tid[CONFIG_CORE_COUNT];

/*
* Privileged thread initialization for userspace LL scheduling.
* Creates the scheduling thread, sets up timer, grants access to kernel
Expand Down Expand Up @@ -343,6 +351,9 @@ static int zephyr_domain_thread_init(struct ll_schedule_domain *domain,
INT_TO_POINTER(core), NULL, CONFIG_LL_THREAD_PRIORITY,
K_USER, K_FOREVER);

/* record in the kernel-only table for syscall-context lookups */
ll_thread_tid[core] = dt->ll_thread;

#ifdef CONFIG_SCHED_CPU_MASK
k_thread_cpu_pin(thread, core);
#endif
Expand Down Expand Up @@ -477,6 +488,7 @@ static void zephyr_domain_thread_free(struct ll_schedule_domain *domain,
k_thread_abort(dt->ll_thread);
k_object_free(dt->ll_thread);
dt->ll_thread = NULL;
ll_thread_tid[core] = NULL;
}

if (dt->sem) {
Expand All @@ -498,6 +510,21 @@ struct k_thread *zephyr_domain_thread_tid(struct ll_schedule_domain *domain)
return dt->ll_thread;
}

/*
* Return the LL scheduling thread for an explicitly given core.
*
* Reads a kernel-only table keyed by core, so it is safe to call from a
* privileged syscall context without dereferencing any user-accessible
* scheduler or domain object, and without relying on cpu_get_id().
*/
struct k_thread *zephyr_domain_thread_tid_for_core(int core)
{
if (core < 0 || core >= CONFIG_CORE_COUNT)
return NULL;

return ll_thread_tid[core];
}

#endif /* CONFIG_SOF_USERSPACE_LL */

#if CONFIG_CROSS_CORE_STREAM
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19 changes: 19 additions & 0 deletions src/schedule/zephyr_ll.c
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Expand Up @@ -474,6 +474,25 @@ int z_impl_zephyr_ll_task_sem_alloc(struct task *task)

k_sem_init(ts->sem, 0, 1);

#if CONFIG_SOF_USERSPACE_LL
/*
* The per-task semaphore is signalled from zephyr_ll_task_done(),
* which runs in the (unprivileged) LL scheduler thread when a task is
* freed while it is still running. k_object_alloc() only grants access
* to the calling thread (the IPC handler that creates the task), so the
* LL thread must be granted access explicitly, otherwise its
* k_sem_give() traps with a userspace permission fault.
*
* Resolve the LL thread from kernel-only per-core state keyed by the
* task's target core; never traverse the user-accessible scheduler or
* domain objects from privileged context.
*/
struct k_thread *ll_tid = zephyr_domain_thread_tid_for_core(task->core);

@lyakh lyakh Aug 17, 2026 •
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isn't k_thread deprecated and we have to use k_tid_t?

@kv2019i kv2019i Aug 17, 2026 •
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@lyakh Is it deprecated? The value we return here is passed to k_object_access_grant() which takes "struct k_thread *" as argument. But OTOH, upstream Zephyr test code now passes k_current_get() to k_object_access_grant() (and k_current_get() returns k_tid_t). The function name has "thread_tid_for_core", so maybe I'll change for k_tid_t...
UPDATE: I think I'll keep it like this. We only store "struct k_thread*" in zephyr_domain.c. There is no function to convert a "struct k_thread *" to k_tid_t (they are the same thing, it's just a cast in zephyr thread.c). We could of course add another field to store also the k_tid_t in "struct zephyr_domain_thread", but that seems a bit silly (as the values are always the same). I think as long as Zephyr's thread.c just casts the types, we can do the same.

@lyakh lyakh Aug 18, 2026 •
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@lyakh Is it deprecated? The value we return here is passed to k_object_access_grant() which takes "struct k_thread " as argument. But OTOH, upstream Zephyr test code now passes k_current_get() to k_object_access_grant() (and k_current_get() returns k_tid_t). The function name has "thread_tid_for_core", so maybe I'll change for k_tid_t... UPDATE: I think I'll keep it like this. We only store "struct k_thread" in zephyr_domain.c. There is no function to convert a "struct k_thread *" to k_tid_t (they are the same thing, it's just a cast in zephyr thread.c). We could of course add another field to store also the k_tid_t in "struct zephyr_domain_thread", but that seems a bit silly (as the values are always the same). I think as long as Zephyr's thread.c just casts the types, we can do the same.

@kv2019i ah, oh, sorry, not really. It's only deprecated in one specific case https://github.com/zephyrproject-rtos/zephyr/blob/6b0261c4f6761b4250faf598acd8b21d36de31b4/include/zephyr/kernel.h#L4911 - that bit me at some point but then I forgot what exactly it was...


if (ll_tid)
k_thread_access_grant(ll_tid, ts->sem);
#endif

ts->task = task;
pdata->sem_p = ts->sem;
/* List is protected by IPC serialization */
Expand Down
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