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The rcuwait utility provides an efficient and safe single wait/wake mechanism. It is used in situations where queued wait is the wrong semantics, and often too bulky. For example, cases where the wait is already done under a lock. In the past, rcuwait has been extended to support beyond only uninterruptible sleep, and similarly, there are users that can benefit for the addition of timeouts. As such, tntroduce rcuwait_wait_event_timeout(), with semantics equivalent to calls for queued wait counterparts. Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Davidlohr Bueso <dave@stgolabs.net> Link: https://lore.kernel.org/r/20230523170927.20685-2-dave@stgolabs.net Signed-off-by: Dan Williams <dan.j.williams@intel.com>
94 lines
2.3 KiB
C
94 lines
2.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_RCUWAIT_H_
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#define _LINUX_RCUWAIT_H_
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#include <linux/rcupdate.h>
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#include <linux/sched/signal.h>
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/*
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* rcuwait provides a way of blocking and waking up a single
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* task in an rcu-safe manner.
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*
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* The only time @task is non-nil is when a user is blocked (or
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* checking if it needs to) on a condition, and reset as soon as we
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* know that the condition has succeeded and are awoken.
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*/
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struct rcuwait {
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struct task_struct __rcu *task;
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};
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#define __RCUWAIT_INITIALIZER(name) \
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{ .task = NULL, }
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static inline void rcuwait_init(struct rcuwait *w)
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{
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w->task = NULL;
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}
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/*
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* Note: this provides no serialization and, just as with waitqueues,
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* requires care to estimate as to whether or not the wait is active.
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*/
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static inline int rcuwait_active(struct rcuwait *w)
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{
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return !!rcu_access_pointer(w->task);
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}
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extern int rcuwait_wake_up(struct rcuwait *w);
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/*
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* The caller is responsible for locking around rcuwait_wait_event(),
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* and [prepare_to/finish]_rcuwait() such that writes to @task are
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* properly serialized.
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*/
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static inline void prepare_to_rcuwait(struct rcuwait *w)
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{
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rcu_assign_pointer(w->task, current);
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}
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extern void finish_rcuwait(struct rcuwait *w);
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#define ___rcuwait_wait_event(w, condition, state, ret, cmd) \
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({ \
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long __ret = ret; \
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prepare_to_rcuwait(w); \
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for (;;) { \
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/* \
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* Implicit barrier (A) pairs with (B) in \
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* rcuwait_wake_up(). \
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*/ \
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set_current_state(state); \
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if (condition) \
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break; \
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\
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if (signal_pending_state(state, current)) { \
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__ret = -EINTR; \
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break; \
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} \
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\
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cmd; \
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} \
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finish_rcuwait(w); \
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__ret; \
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})
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#define rcuwait_wait_event(w, condition, state) \
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___rcuwait_wait_event(w, condition, state, 0, schedule())
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#define __rcuwait_wait_event_timeout(w, condition, state, timeout) \
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___rcuwait_wait_event(w, ___wait_cond_timeout(condition), \
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state, timeout, \
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__ret = schedule_timeout(__ret))
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#define rcuwait_wait_event_timeout(w, condition, state, timeout) \
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({ \
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long __ret = timeout; \
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if (!___wait_cond_timeout(condition)) \
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__ret = __rcuwait_wait_event_timeout(w, condition, \
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state, timeout); \
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__ret; \
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})
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#endif /* _LINUX_RCUWAIT_H_ */
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