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sched/wait: Add a waitqueue helper for fully exclusive priority waiters

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Add a waitqueue helper to add a priority waiter that requires exclusive
wakeups, i.e. that requires that it be the _only_ priority waiter.  The
API will be used by KVM to ensure that at most one of KVM's irqfds is
bound to a single eventfd (across the entire kernel).

Open code the helper instead of using __add_wait_queue() so that the
common path doesn't need to "handle" impossible failures.

Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250522235223.3178519-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2025-06-23 09:50:58 -07:00
parent a52664134a
commit 0d09582b3a
2 changed files with 20 additions and 0 deletions
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include/linux/wait.h
+2
View File
@@ -164,6 +164,8 @@ static inline bool wq_has_sleeper(struct wait_queue_head *wq_head)
extern void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry);
extern void add_wait_queue_exclusive(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry);
extern void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry);
extern int add_wait_queue_priority_exclusive(struct wait_queue_head *wq_head,
struct wait_queue_entry *wq_entry);
extern void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry);
static inline void __add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
kernel/sched/wait.c
+18
View File
@@ -47,6 +47,24 @@ void add_wait_queue_priority(struct wait_queue_head *wq_head, struct wait_queue_
}
EXPORT_SYMBOL_GPL(add_wait_queue_priority);
int add_wait_queue_priority_exclusive(struct wait_queue_head *wq_head,
struct wait_queue_entry *wq_entry)
{
struct list_head *head = &wq_head->head;
wq_entry->flags |= WQ_FLAG_EXCLUSIVE | WQ_FLAG_PRIORITY;
guard(spinlock_irqsave)(&wq_head->lock);
if (!list_empty(head) &&
(list_first_entry(head, typeof(*wq_entry), entry)->flags & WQ_FLAG_PRIORITY))
return -EBUSY;
list_add(&wq_entry->entry, head);
return 0;
}
EXPORT_SYMBOL_GPL(add_wait_queue_priority_exclusive);
void remove_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq_entry)
{
unsigned long flags;