From f3b0813aeee2c98d1f01b1db1d7d7059cf0a240a Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= Date: Tue, 15 Dec 2015 11:20:20 +0000 Subject: [PATCH] hyperv/kvp: wake up the daemon if it's sleeping due to poll() 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 Sponsored by: Microsoft OSTC Reviewed by: delphij, royger MFC after: 3 days Differential Revision: https://reviews.freebsd.org/D4258 --- sys/dev/hyperv/utilities/hv_kvp.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/sys/dev/hyperv/utilities/hv_kvp.c b/sys/dev/hyperv/utilities/hv_kvp.c index 4598510bb8d..58d565c44bf 100644 --- a/sys/dev/hyperv/utilities/hv_kvp.c +++ b/sys/dev/hyperv/utilities/hv_kvp.c @@ -44,6 +44,7 @@ __FBSDID("$FreeBSD$"); #include #include #include +#include #include #include #include @@ -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);