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xen/evtchn: use READ/WRITE_ONCE() for accessing ring indices 

For avoiding read- and write-tearing by the compiler use READ_ONCE()
and WRITE_ONCE() for accessing the ring indices in evtchn.c.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20210219154030.10892-9-jgross@suse.com
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
This commit is contained in:
Juergen Gross 2021-02-19 16:40:30 +01:00 committed by Boris Ostrovsky
parent d566995940
commit 6977c0b560
1 changed files with 16 additions and 9 deletions
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25
drivers/xen/evtchn.c
View File

@ -162,6 +162,7 @@ static irqreturn_t evtchn_interrupt(int irq, void *data)
{
struct user_evtchn *evtchn = data;
struct per_user_data *u = evtchn->user;
unsigned int prod, cons;
WARN(!evtchn->enabled,
"Interrupt for port %u, but apparently not enabled; per-user %p\n",
@ -171,10 +172,14 @@ static irqreturn_t evtchn_interrupt(int irq, void *data)
spin_lock(&u->ring_prod_lock);
if ((u->ring_prod - u->ring_cons) < u->ring_size) {
*evtchn_ring_entry(u, u->ring_prod) = evtchn->port;
prod = READ_ONCE(u->ring_prod);
cons = READ_ONCE(u->ring_cons);
if ((prod - cons) < u->ring_size) {
*evtchn_ring_entry(u, prod) = evtchn->port;
smp_wmb(); /* Ensure ring contents visible */
if (u->ring_cons == u->ring_prod++) {
WRITE_ONCE(u->ring_prod, prod + 1);
if (cons == prod) {
wake_up_interruptible(&u->evtchn_wait);
kill_fasync(&u->evtchn_async_queue,
SIGIO, POLL_IN);
@ -210,8 +215,8 @@ static ssize_t evtchn_read(struct file *file, char __user *buf,
if (u->ring_overflow)
goto unlock_out;
c = u->ring_cons;
p = u->ring_prod;
c = READ_ONCE(u->ring_cons);
p = READ_ONCE(u->ring_prod);
if (c != p)
break;
@ -221,7 +226,7 @@ static ssize_t evtchn_read(struct file *file, char __user *buf,
return -EAGAIN;
rc = wait_event_interruptible(u->evtchn_wait,
u->ring_cons != u->ring_prod);
READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod));
if (rc)
return rc;
}
@ -251,7 +256,7 @@ static ssize_t evtchn_read(struct file *file, char __user *buf,
copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
goto unlock_out;
u->ring_cons += (bytes1 + bytes2) / sizeof(evtchn_port_t);
WRITE_ONCE(u->ring_cons, c + (bytes1 + bytes2) / sizeof(evtchn_port_t));
rc = bytes1 + bytes2;
unlock_out:
@ -552,7 +557,9 @@ static long evtchn_ioctl(struct file *file,
/* Initialise the ring to empty. Clear errors. */
mutex_lock(&u->ring_cons_mutex);
spin_lock_irq(&u->ring_prod_lock);
u->ring_cons = u->ring_prod = u->ring_overflow = 0;
WRITE_ONCE(u->ring_cons, 0);
WRITE_ONCE(u->ring_prod, 0);
u->ring_overflow = 0;
spin_unlock_irq(&u->ring_prod_lock);
mutex_unlock(&u->ring_cons_mutex);
rc = 0;
@ -595,7 +602,7 @@ static __poll_t evtchn_poll(struct file *file, poll_table *wait)
struct per_user_data *u = file->private_data;
poll_wait(file, &u->evtchn_wait, wait);
if (u->ring_cons != u->ring_prod)
if (READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod))
mask |= EPOLLIN | EPOLLRDNORM;
if (u->ring_overflow)
mask = EPOLLERR;