[PATCH 17/24] xen/dev-evtchn: clean up locking in evtchn

Jeremy Fitzhardinge
2009-03-13T08:20:04Z

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

Define a new per_user_data mutex to serialize bind/unbind operations
to prevent them from racing with each other. Fix error returns
and don't do a bind while holding a spinlock.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
drivers/xen/evtchn.c | 37 +++++++++++++++++++++++++------------
1 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index 517b9ee..af03195 100644
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -54,6 +54,8 @@
#include <asm/xen/hypervisor.h>

struct per_user_data {
+ struct mutex bind_mutex; /* serialize bind/unbind operations */
+
/* Notification ring, accessed via /dev/xen/evtchn. */
#define EVTCHN_RING_SIZE (PAGE_SIZE / sizeof(evtchn_port_t))
#define EVTCHN_RING_MASK(_i) ((_i)&(EVTCHN_RING_SIZE-1))
@@ -69,7 +71,7 @@ struct per_user_data {

/* Who's bound to each port? */
static struct per_user_data *port_user[NR_EVENT_CHANNELS];
-static DEFINE_SPINLOCK(port_user_lock);
+static DEFINE_SPINLOCK(port_user_lock); /* protects port_user[] and ring_prod */

irqreturn_t evtchn_interrupt(int irq, void *data)
{
@@ -210,22 +212,24 @@ static ssize_t evtchn_write(struct file *file, const char __user *buf,

static int evtchn_bind_to_user(struct per_user_data *u, int port)
{
- int irq;
int rc = 0;

- spin_lock_irq(&port_user_lock);
-
+ /*
+ * Ports are never reused, so every caller should pass in a
+ * unique port.
+ *
+ * (Locking not necessary because we haven't registered the
+ * interrupt handler yet, and our caller has already
+ * serialized bind operations.)
+ */
BUG_ON(port_user[port] != NULL);
-
- irq = bind_evtchn_to_irqhandler(port, evtchn_interrupt, IRQF_DISABLED,
- u->name, (void *)(unsigned long)port);
- if (rc < 0)
- goto fail;
-
port_user[port] = u;

-fail:
- spin_unlock_irq(&port_user_lock);
+ rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, IRQF_DISABLED,
+ u->name, (void *)(unsigned long)port);
+ if (rc >= 0)
+ rc = 0;
+
return rc;
}

@@ -234,6 +238,10 @@ static void evtchn_unbind_from_user(struct per_user_data *u, int port)
int irq = irq_from_evtchn(port);

unbind_from_irqhandler(irq, (void *)(unsigned long)port);
+
+ /* make sure we unbind the irq handler before clearing the port */
+ barrier();
+
port_user[port] = NULL;
}

@@ -244,6 +252,9 @@ static long evtchn_ioctl(struct file *file,
struct per_user_data *u = file->private_data;
void __user *uarg = (void __user *) arg;

+ /* Prevent bind from racing with unbind */
+ mutex_lock(&u->bind_mutex);
+
switch (cmd) {
case IOCTL_EVTCHN_BIND_VIRQ: {
struct ioctl_evtchn_bind_virq bind;
@@ -368,6 +379,7 @@ static long evtchn_ioctl(struct file *file,
rc = -ENOSYS;
break;
}
+ mutex_unlock(&u->bind_mutex);

return rc;
}
@@ -414,6 +426,7 @@ static int evtchn_open(struct inode *inode, struct file *filp)
return -ENOMEM;
}

+ mutex_init(&u->bind_mutex);
mutex_init(&u->ring_cons_mutex);

filp->private_data = u;
--
1.6.0.6