From: Juergen Gross <jgross@suse.com>
To: xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org
Cc: Juergen Gross <jgross@suse.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Stefano Stabellini <sstabellini@kernel.org>
Subject: [PATCH v2 8/8] xen/evtchn: use READ/WRITE_ONCE() for accessing ring indices
Date: Thu, 11 Feb 2021 11:16:16 +0100 [thread overview]
Message-ID: <20210211101616.13788-9-jgross@suse.com> (raw)
In-Reply-To: <20210211101616.13788-1-jgross@suse.com>
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>
---
V2:
- modify all accesses (Julien Grall)
---
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 421382c73d88..620008f89dbe 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++) {
+ if (cons == prod++) {
+ WRITE_ONCE(u->ring_prod, 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;
--
2.26.2
next prev parent reply other threads:[~2021-02-11 10:18 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-11 10:16 [PATCH v2 0/8] xen/events: bug fixes and some diagnostic aids Juergen Gross
2021-02-11 10:16 ` [PATCH v2 1/8] xen/events: reset affinity of 2-level event when tearing it down Juergen Gross
2021-02-14 21:17 ` Julien Grall
2021-02-11 10:16 ` [PATCH v2 2/8] xen/events: don't unmask an event channel when an eoi is pending Juergen Gross
2021-02-11 10:16 ` [PATCH v2 3/8] xen/events: avoid handling the same event on two cpus at the same time Juergen Gross
2021-02-14 21:34 ` Julien Grall
2021-02-15 6:55 ` Jürgen Groß
2021-02-15 21:35 ` Boris Ostrovsky
2021-02-18 11:47 ` Jürgen Groß
2021-02-11 10:16 ` [PATCH v2 4/8] xen/netback: fix spurious event detection for common event case Juergen Gross
2021-02-11 10:53 ` Jan Beulich
2021-02-11 14:15 ` Paul Durrant
2021-02-11 15:24 ` Wei Liu
2021-02-11 10:16 ` [PATCH v2 5/8] xen/events: link interdomain events to associated xenbus device Juergen Gross
2021-02-11 14:16 ` Paul Durrant
2021-02-11 10:16 ` [PATCH v2 6/8] xen/events: add per-xenbus device event statistics and settings Juergen Gross
2021-02-15 21:54 ` Boris Ostrovsky
2021-02-11 10:16 ` [PATCH v2 7/8] xen/evtch: use smp barriers for user event ring Juergen Gross
2021-02-11 10:16 ` Juergen Gross [this message]
2021-02-17 13:29 ` [PATCH v2 8/8] xen/evtchn: use READ/WRITE_ONCE() for accessing ring indices Ross Lagerwall
2021-02-18 11:46 ` Jürgen Groß
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