mirror of
https://github.com/projectacrn/acrn-hypervisor.git
synced 2025-04-29 12:14:13 +00:00
d575edf79a
Currently the sched event handling may encounter data race problem, and
as a result some vcpus might be stalled forever.
One example can be wbinvd handling where more than 1 vcpus are doing
wbinvd concurrently. The following is a possible execution of 3 vcpus:
-------
0 1 2
req [Note: 0]
req bit0 set [Note: 1]
IPI -> 0
req bit2 set
IPI -> 2
VMExit
req bit2 cleared
wait
vcpu2 descheduled
VMExit
req bit0 cleared
wait
vcpu0 descheduled
signal 0
event0->set=true
wake 0
signal 2
event2->set=true [Note: 3]
wake 2
vcpu2 scheduled
event2->set=false
resume
req
req bit0 set
IPI -> 0
req bit1 set
IPI -> 1
(doesn't matter)
vcpu0 scheduled [Note: 4]
signal 0
event0->set=true
(no wake) [Note: 2]
event0->set=false (the rest doesn't matter)
resume
Any VMExit
req bit0 cleared
wait
idle running
(blocked forever)
Notes:
0: req: vcpu_make_request(vcpu, ACRN_REQUEST_WAIT_WBINVD).
1: req bit: Bit in pending_req_bits. Bit0 stands for bit for vcpu0.
2: In function signal_event, At this time the event->waiting_thread
is not NULL, so wake_thread will not execute
3: eventX: struct sched_event of vcpuX.
4: In function wait_event, the lock does not strictly cover the execution between
schedule() and event->set=false, so other threads may kick in.
-----
As shown in above example, before the last random VMExit, vcpu0 ended up
with request bit set but event->set==false, so blocked forever.
This patch proposes to change event->set from a boolean variable to an
integer. The semantic is very similar to a semaphore. The wait_event
will add 1 to this value, and block when this value is > 0, whereas signal_event
will decrease this value by 1.
It may happen that this value was decreased to a negative number but that
is OK. As long as the wait_event and signal_event are paired and
program order is observed (that is, wait_event always happens-before signal_event
on a single vcpu), this value will eventually be 0.
Tracked-On: #6405
Signed-off-by: Yifan Liu <yifan1.liu@intel.com>
58 lines
1.4 KiB
C
58 lines
1.4 KiB
C
/*
|
|
* Copyright (C) 2018 Intel Corporation. All rights reserved.
|
|
*
|
|
* SPDX-License-Identifier: BSD-3-Clause
|
|
*/
|
|
#include <asm/cpu.h>
|
|
#include <schedule.h>
|
|
#include <event.h>
|
|
#include <logmsg.h>
|
|
|
|
void init_event(struct sched_event *event)
|
|
{
|
|
spinlock_init(&event->lock);
|
|
event->nqueued = 0;
|
|
event->waiting_thread = NULL;
|
|
}
|
|
|
|
void reset_event(struct sched_event *event)
|
|
{
|
|
uint64_t rflag;
|
|
|
|
spinlock_irqsave_obtain(&event->lock, &rflag);
|
|
event->nqueued = 0;
|
|
event->waiting_thread = NULL;
|
|
spinlock_irqrestore_release(&event->lock, rflag);
|
|
}
|
|
|
|
/* support exclusive waiting only */
|
|
void wait_event(struct sched_event *event)
|
|
{
|
|
uint64_t rflag;
|
|
|
|
spinlock_irqsave_obtain(&event->lock, &rflag);
|
|
ASSERT((event->waiting_thread == NULL), "only support exclusive waiting");
|
|
event->waiting_thread = sched_get_current(get_pcpu_id());
|
|
event->nqueued++;
|
|
while ((event->nqueued > 0) && (event->waiting_thread != NULL)) {
|
|
sleep_thread(event->waiting_thread);
|
|
spinlock_irqrestore_release(&event->lock, rflag);
|
|
schedule();
|
|
spinlock_irqsave_obtain(&event->lock, &rflag);
|
|
}
|
|
event->waiting_thread = NULL;
|
|
spinlock_irqrestore_release(&event->lock, rflag);
|
|
}
|
|
|
|
void signal_event(struct sched_event *event)
|
|
{
|
|
uint64_t rflag;
|
|
|
|
spinlock_irqsave_obtain(&event->lock, &rflag);
|
|
event->nqueued--;
|
|
if (event->waiting_thread != NULL) {
|
|
wake_thread(event->waiting_thread);
|
|
}
|
|
spinlock_irqrestore_release(&event->lock, rflag);
|
|
}
|