kevin/linux
1
Fork 0
Code
57a1a19763
linux/drivers/xen/evtchn.c
David Vrabel 179fbd5a45 xen/evtchn: avoid a deadlock when unbinding an event channel 
Unbinding an event channel (either with the ioctl or when the evtchn
device is closed) may deadlock because disable_irq() is called with
port_user_lock held which is also locked by the interrupt handler.

Think of the IOCTL_EVTCHN_UNBIND is being serviced, the routine has
just taken the lock, and an interrupt happens. The evtchn_interrupt
is invoked, tries to take the lock and spins forever.

A quick glance at the code shows that the spinlock is a local IRQ
variant. Unfortunately that does not help as "disable_irq() waits for
the interrupt handler on all CPUs to stop running.  If the irq occurs
on another VCPU, it tries to take port_user_lock and can't because
the unbind ioctl is holding it." (from David). Hence we cannot
depend on the said spinlock to protect us. We could make it a system
wide IRQ disable spinlock but there is a better way.

We can piggyback on the fact that the existence of the spinlock is
to make get_port_user() checks be up-to-date. And we can alter those
checks to not depend on the spin lock (as it's protected by u->bind_mutex
in the ioctl) and can remove the unnecessary locking (this is
IOCTL_EVTCHN_UNBIND) path.

In the interrupt handler we cannot use the mutex, but we do not
need it.

"The unbind disables the irq before making the port user stale, so when
you clear it you are guaranteed that the interrupt handler that might
use that port cannot be running." (from David).

Hence this patch removes the spinlock usage on the teardown path
and piggybacks on disable_irq happening before we muck with the
get_port_user() data. This ensures that the interrupt handler will
never run on stale data.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[v1: Expanded the commit description a bit]
2013-07-30 09:21:14 -04:00

556 lines
13 KiB
C
Raw Blame History

/******************************************************************************
* evtchn.c
*
* Driver for receiving and demuxing event-channel signals.
*
* Copyright (c) 2004-2005, K A Fraser
* Multi-process extensions Copyright (c) 2004, Steven Smith
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation; or, when distributed
* separately from the Linux kernel or incorporated into other
* software packages, subject to the following license:
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this source file (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use, copy, modify,
* merge, publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
#define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/major.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/poll.h>
#include <linux/irq.h>
#include <linux/init.h>
#include <linux/mutex.h>
#include <linux/cpu.h>
#include <xen/xen.h>
#include <xen/events.h>
#include <xen/evtchn.h>
#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))
evtchn_port_t *ring;
unsigned int ring_cons, ring_prod, ring_overflow;
struct mutex ring_cons_mutex; /* protect against concurrent readers */
/* Processes wait on this queue when ring is empty. */
wait_queue_head_t evtchn_wait;
struct fasync_struct *evtchn_async_queue;
const char *name;
};
/*
* Who's bound to each port? This is logically an array of struct
* per_user_data *, but we encode the current enabled-state in bit 0.
*/
static unsigned long *port_user;
static DEFINE_SPINLOCK(port_user_lock); /* protects port_user[] and ring_prod */
static inline struct per_user_data *get_port_user(unsigned port)
{
return (struct per_user_data *)(port_user[port] & ~1);
}
static inline void set_port_user(unsigned port, struct per_user_data *u)
{
port_user[port] = (unsigned long)u;
}
static inline bool get_port_enabled(unsigned port)
{
return port_user[port] & 1;
}
static inline void set_port_enabled(unsigned port, bool enabled)
{
if (enabled)
port_user[port] |= 1;
else
port_user[port] &= ~1;
}
static irqreturn_t evtchn_interrupt(int irq, void *data)
{
unsigned int port = (unsigned long)data;
struct per_user_data *u;
spin_lock(&port_user_lock);
u = get_port_user(port);
WARN(!get_port_enabled(port),
"Interrupt for port %d, but apparently not enabled; per-user %p\n",
port, u);
disable_irq_nosync(irq);
set_port_enabled(port, false);
if ((u->ring_prod - u->ring_cons) < EVTCHN_RING_SIZE) {
u->ring[EVTCHN_RING_MASK(u->ring_prod)] = port;
wmb(); /* Ensure ring contents visible */
if (u->ring_cons == u->ring_prod++) {
wake_up_interruptible(&u->evtchn_wait);
kill_fasync(&u->evtchn_async_queue,
SIGIO, POLL_IN);
}
} else
u->ring_overflow = 1;
spin_unlock(&port_user_lock);
return IRQ_HANDLED;
}
static ssize_t evtchn_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
int rc;
unsigned int c, p, bytes1 = 0, bytes2 = 0;
struct per_user_data *u = file->private_data;
/* Whole number of ports. */
count &= ~(sizeof(evtchn_port_t)-1);
if (count == 0)
return 0;
if (count > PAGE_SIZE)
count = PAGE_SIZE;
for (;;) {
mutex_lock(&u->ring_cons_mutex);
rc = -EFBIG;
if (u->ring_overflow)
goto unlock_out;
c = u->ring_cons;
p = u->ring_prod;
if (c != p)
break;
mutex_unlock(&u->ring_cons_mutex);
if (file->f_flags & O_NONBLOCK)
return -EAGAIN;
rc = wait_event_interruptible(u->evtchn_wait,
u->ring_cons != u->ring_prod);
if (rc)
return rc;
}
/* Byte lengths of two chunks. Chunk split (if any) is at ring wrap. */
if (((c ^ p) & EVTCHN_RING_SIZE) != 0) {
bytes1 = (EVTCHN_RING_SIZE - EVTCHN_RING_MASK(c)) *
sizeof(evtchn_port_t);
bytes2 = EVTCHN_RING_MASK(p) * sizeof(evtchn_port_t);
} else {
bytes1 = (p - c) * sizeof(evtchn_port_t);
bytes2 = 0;
}
/* Truncate chunks according to caller's maximum byte count. */
if (bytes1 > count) {
bytes1 = count;
bytes2 = 0;
} else if ((bytes1 + bytes2) > count) {
bytes2 = count - bytes1;
}
rc = -EFAULT;
rmb(); /* Ensure that we see the port before we copy it. */
if (copy_to_user(buf, &u->ring[EVTCHN_RING_MASK(c)], bytes1) ||
((bytes2 != 0) &&
copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
goto unlock_out;
u->ring_cons += (bytes1 + bytes2) / sizeof(evtchn_port_t);
rc = bytes1 + bytes2;
unlock_out:
mutex_unlock(&u->ring_cons_mutex);
return rc;
}
static ssize_t evtchn_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
int rc, i;
evtchn_port_t *kbuf = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
struct per_user_data *u = file->private_data;
if (kbuf == NULL)
return -ENOMEM;
/* Whole number of ports. */
count &= ~(sizeof(evtchn_port_t)-1);
rc = 0;
if (count == 0)
goto out;
if (count > PAGE_SIZE)
count = PAGE_SIZE;
rc = -EFAULT;
if (copy_from_user(kbuf, buf, count) != 0)
goto out;
spin_lock_irq(&port_user_lock);
for (i = 0; i < (count/sizeof(evtchn_port_t)); i++) {
unsigned port = kbuf[i];
if (port < NR_EVENT_CHANNELS &&
get_port_user(port) == u &&
!get_port_enabled(port)) {
set_port_enabled(port, true);
enable_irq(irq_from_evtchn(port));
}
}
spin_unlock_irq(&port_user_lock);
rc = count;
out:
free_page((unsigned long)kbuf);
return rc;
}
static int evtchn_bind_to_user(struct per_user_data *u, int port)
{
int rc = 0;
/*
* 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(get_port_user(port) != NULL);
set_port_user(port, u);
set_port_enabled(port, true); /* start enabled */
rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, IRQF_DISABLED,
u->name, (void *)(unsigned long)port);
if (rc >= 0)
rc = evtchn_make_refcounted(port);
else {
/* bind failed, should close the port now */
struct evtchn_close close;
close.port = port;
if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
BUG();
set_port_user(port, NULL);
}
return rc;
}
static void evtchn_unbind_from_user(struct per_user_data *u, int port)
{
int irq = irq_from_evtchn(port);
BUG_ON(irq < 0);
unbind_from_irqhandler(irq, (void *)(unsigned long)port);
set_port_user(port, NULL);
}
static long evtchn_ioctl(struct file *file,
unsigned int cmd, unsigned long arg)
{
int rc;
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;
struct evtchn_bind_virq bind_virq;
rc = -EFAULT;
if (copy_from_user(&bind, uarg, sizeof(bind)))
break;
bind_virq.virq = bind.virq;
bind_virq.vcpu = 0;
rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_virq,
&bind_virq);
if (rc != 0)
break;
rc = evtchn_bind_to_user(u, bind_virq.port);
if (rc == 0)
rc = bind_virq.port;
break;
}
case IOCTL_EVTCHN_BIND_INTERDOMAIN: {
struct ioctl_evtchn_bind_interdomain bind;
struct evtchn_bind_interdomain bind_interdomain;
rc = -EFAULT;
if (copy_from_user(&bind, uarg, sizeof(bind)))
break;
bind_interdomain.remote_dom = bind.remote_domain;
bind_interdomain.remote_port = bind.remote_port;
rc = HYPERVISOR_event_channel_op(EVTCHNOP_bind_interdomain,
&bind_interdomain);
if (rc != 0)
break;
rc = evtchn_bind_to_user(u, bind_interdomain.local_port);
if (rc == 0)
rc = bind_interdomain.local_port;
break;
}
case IOCTL_EVTCHN_BIND_UNBOUND_PORT: {
struct ioctl_evtchn_bind_unbound_port bind;
struct evtchn_alloc_unbound alloc_unbound;
rc = -EFAULT;
if (copy_from_user(&bind, uarg, sizeof(bind)))
break;
alloc_unbound.dom = DOMID_SELF;
alloc_unbound.remote_dom = bind.remote_domain;
rc = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound,
&alloc_unbound);
if (rc != 0)
break;
rc = evtchn_bind_to_user(u, alloc_unbound.port);
if (rc == 0)
rc = alloc_unbound.port;
break;
}
case IOCTL_EVTCHN_UNBIND: {
struct ioctl_evtchn_unbind unbind;
rc = -EFAULT;
if (copy_from_user(&unbind, uarg, sizeof(unbind)))
break;
rc = -EINVAL;
if (unbind.port >= NR_EVENT_CHANNELS)
break;
rc = -ENOTCONN;
if (get_port_user(unbind.port) != u)
break;
disable_irq(irq_from_evtchn(unbind.port));
evtchn_unbind_from_user(u, unbind.port);
rc = 0;
break;
}
case IOCTL_EVTCHN_NOTIFY: {
struct ioctl_evtchn_notify notify;
rc = -EFAULT;
if (copy_from_user(&notify, uarg, sizeof(notify)))
break;
if (notify.port >= NR_EVENT_CHANNELS) {
rc = -EINVAL;
} else if (get_port_user(notify.port) != u) {
rc = -ENOTCONN;
} else {
notify_remote_via_evtchn(notify.port);
rc = 0;
}
break;
}
case IOCTL_EVTCHN_RESET: {
/* Initialise the ring to empty. Clear errors. */
mutex_lock(&u->ring_cons_mutex);
spin_lock_irq(&port_user_lock);
u->ring_cons = u->ring_prod = u->ring_overflow = 0;
spin_unlock_irq(&port_user_lock);
mutex_unlock(&u->ring_cons_mutex);
rc = 0;
break;
}
default:
rc = -ENOSYS;
break;
}
mutex_unlock(&u->bind_mutex);
return rc;
}
static unsigned int evtchn_poll(struct file *file, poll_table *wait)
{
unsigned int mask = POLLOUT | POLLWRNORM;
struct per_user_data *u = file->private_data;
poll_wait(file, &u->evtchn_wait, wait);
if (u->ring_cons != u->ring_prod)
mask |= POLLIN | POLLRDNORM;
if (u->ring_overflow)
mask = POLLERR;
return mask;
}
static int evtchn_fasync(int fd, struct file *filp, int on)
{
struct per_user_data *u = filp->private_data;
return fasync_helper(fd, filp, on, &u->evtchn_async_queue);
}
static int evtchn_open(struct inode *inode, struct file *filp)
{
struct per_user_data *u;
u = kzalloc(sizeof(*u), GFP_KERNEL);
if (u == NULL)
return -ENOMEM;
u->name = kasprintf(GFP_KERNEL, "evtchn:%s", current->comm);
if (u->name == NULL) {
kfree(u);
return -ENOMEM;
}
init_waitqueue_head(&u->evtchn_wait);
u->ring = (evtchn_port_t *)__get_free_page(GFP_KERNEL);
if (u->ring == NULL) {
kfree(u->name);
kfree(u);
return -ENOMEM;
}
mutex_init(&u->bind_mutex);
mutex_init(&u->ring_cons_mutex);
filp->private_data = u;
return nonseekable_open(inode, filp);
}
static int evtchn_release(struct inode *inode, struct file *filp)
{
int i;
struct per_user_data *u = filp->private_data;
for (i = 0; i < NR_EVENT_CHANNELS; i++) {
if (get_port_user(i) != u)
continue;
disable_irq(irq_from_evtchn(i));
evtchn_unbind_from_user(get_port_user(i), i);
}
free_page((unsigned long)u->ring);
kfree(u->name);
kfree(u);
return 0;
}
static const struct file_operations evtchn_fops = {
.owner = THIS_MODULE,
.read = evtchn_read,
.write = evtchn_write,
.unlocked_ioctl = evtchn_ioctl,
.poll = evtchn_poll,
.fasync = evtchn_fasync,
.open = evtchn_open,
.release = evtchn_release,
.llseek = no_llseek,
};
static struct miscdevice evtchn_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "xen/evtchn",
.fops = &evtchn_fops,
};
static int __init evtchn_init(void)
{
int err;
if (!xen_domain())
return -ENODEV;
port_user = kcalloc(NR_EVENT_CHANNELS, sizeof(*port_user), GFP_KERNEL);
if (port_user == NULL)
return -ENOMEM;
spin_lock_init(&port_user_lock);
/* Create '/dev/xen/evtchn'. */
err = misc_register(&evtchn_miscdev);
if (err != 0) {
pr_err("Could not register /dev/xen/evtchn\n");
return err;
}
pr_info("Event-channel device installed\n");
return 0;
}
static void __exit evtchn_cleanup(void)
{
kfree(port_user);
port_user = NULL;
misc_deregister(&evtchn_miscdev);
}
module_init(evtchn_init);
module_exit(evtchn_cleanup);
MODULE_LICENSE("GPL");
View Git Blame Copy Permalink