Commit 6977c0b5 authored by Juergen Gross's avatar Juergen Gross Committed by Boris Ostrovsky
Browse files

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: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20210219154030.10892-9-jgross@suse.com


Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
parent d5669959

drivers/xen/evtchn.c

+16 −9
Original line number Diff line number Diff line
@@ -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;