linux-stable/include/linux/rcuwait.h
Paolo Bonzini febd668d37 rcuwait: avoid lockdep splats from rcuwait_active()
rcuwait_active only returns whether w->task is not NULL.  This is
exactly one of the usecases that are mentioned in the documentation
for rcu_access_pointer() where it is correct to bypass lockdep checks.

This avoids a splat from kvm_vcpu_on_spin().

Reported-by: Wanpeng Li <kernellwp@gmail.com>
Tested-by: Wanpeng Li <kernellwp@gmail.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2020-05-20 03:39:40 -04:00

80 lines
1.8 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_RCUWAIT_H_
#define _LINUX_RCUWAIT_H_
#include <linux/rcupdate.h>
#include <linux/sched/signal.h>
/*
* rcuwait provides a way of blocking and waking up a single
* task in an rcu-safe manner.
*
* The only time @task is non-nil is when a user is blocked (or
* checking if it needs to) on a condition, and reset as soon as we
* know that the condition has succeeded and are awoken.
*/
struct rcuwait {
struct task_struct __rcu *task;
};
#define __RCUWAIT_INITIALIZER(name) \
{ .task = NULL, }
static inline void rcuwait_init(struct rcuwait *w)
{
w->task = NULL;
}
/*
* Note: this provides no serialization and, just as with waitqueues,
* requires care to estimate as to whether or not the wait is active.
*/
static inline int rcuwait_active(struct rcuwait *w)
{
return !!rcu_access_pointer(w->task);
}
extern int rcuwait_wake_up(struct rcuwait *w);
/*
* The caller is responsible for locking around rcuwait_wait_event(),
* and [prepare_to/finish]_rcuwait() such that writes to @task are
* properly serialized.
*/
static inline void prepare_to_rcuwait(struct rcuwait *w)
{
rcu_assign_pointer(w->task, current);
}
static inline void finish_rcuwait(struct rcuwait *w)
{
rcu_assign_pointer(w->task, NULL);
__set_current_state(TASK_RUNNING);
}
#define rcuwait_wait_event(w, condition, state) \
({ \
int __ret = 0; \
prepare_to_rcuwait(w); \
for (;;) { \
/* \
* Implicit barrier (A) pairs with (B) in \
* rcuwait_wake_up(). \
*/ \
set_current_state(state); \
if (condition) \
break; \
\
if (signal_pending_state(state, current)) { \
__ret = -EINTR; \
break; \
} \
\
schedule(); \
} \
finish_rcuwait(w); \
__ret; \
})
#endif /* _LINUX_RCUWAIT_H_ */