From 6977c0b560f190d0d4786f99d9c120126fe654f2 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Fri, 19 Feb 2021 16:40:30 +0100 Subject: [PATCH] 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 Reviewed-by: Boris Ostrovsky Link: https://lore.kernel.org/r/20210219154030.10892-9-jgross@suse.com Signed-off-by: Boris Ostrovsky --- drivers/xen/evtchn.c | 25 ++++++++++++++++--------- 1 file changed, 16 insertions(+), 9 deletions(-) diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c index 421382c..c99415a 100644 --- a/drivers/xen/evtchn.c +++ b/drivers/xen/evtchn.c @@ -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; -- 2.7.4