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hyperv/kvp: wake up the daemon if it's sleeping due to poll()

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Without the patch, there is a race condition: when poll() is invoked(),
if kvp_globals.daemon_busy is false, the daemon won't be timely
woke up, because hv_kvp_send_msg_to_daemon() can't wake up the daemon
in this case.

Submitted by:           Dexuan Cui <decui@microsoft.com>
Sponsored by:		Microsoft OSTC
Reviewed by:		delphij, royger
MFC after:		3 days
Differential Revision:	https://reviews.freebsd.org/D4258
This commit is contained in:
Roger Pau Monné 2015-12-15 11:20:20 +00:00
parent 46b9aa2766
commit f3b0813aee
1 changed files with 10 additions and 1 deletions
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11
sys/dev/hyperv/utilities/hv_kvp.c
View File

@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$");
#include <sys/reboot.h>
#include <sys/lock.h>
#include <sys/taskqueue.h>
#include <sys/selinfo.h>
#include <sys/sysctl.h>
#include <sys/poll.h>
#include <sys/proc.h>
@ -114,6 +115,8 @@ static struct cdev *hv_kvp_dev;
static struct hv_kvp_msg *hv_kvp_dev_buf;
struct proc *daemon_task;
static struct selinfo hv_kvp_selinfo;
/*
* Global state to track and synchronize multiple
* KVP transaction requests from the host.
@ -628,6 +631,9 @@ hv_kvp_send_msg_to_daemon(void)
/* Send the msg to user via function deamon_read - setting sema */
sema_post(&kvp_globals.dev_sema);
/* We should wake up the daemon, in case it's doing poll() */
selwakeup(&hv_kvp_selinfo);
}
@ -940,7 +946,7 @@ hv_kvp_dev_daemon_write(struct cdev *dev __unused, struct uio *uio, int ioflag _
* for daemon to read.
*/
static int
hv_kvp_dev_daemon_poll(struct cdev *dev __unused, int events, struct thread *td __unused)
hv_kvp_dev_daemon_poll(struct cdev *dev __unused, int events, struct thread *td)
{
int revents = 0;
@ -953,6 +959,9 @@ hv_kvp_dev_daemon_poll(struct cdev *dev __unused, int events, struct thread *td
*/
if (kvp_globals.daemon_busy == true)
revents = POLLIN;
else
selrecord(td, &hv_kvp_selinfo);
mtx_unlock(&kvp_globals.pending_mutex);
return (revents);