xen/mce: add .poll method for mcelog device driver
If a driver leaves its poll method NULL, the device is assumed to
be both readable and writable without blocking.
This patch add .poll method to xen mcelog device driver, so that
when mcelog use system calls like ppoll or select, it would be
blocked when no data available, and avoid spinning at CPU.
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Liu, Jinsong <jinsong.liu@intel.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/mcelog.c b/drivers/xen/mcelog.c
index 804aa3c..8feee08 100644
--- a/drivers/xen/mcelog.c
+++ b/drivers/xen/mcelog.c
@@ -41,6 +41,8 @@
#include <linux/miscdevice.h>
#include <linux/uaccess.h>
#include <linux/capability.h>
+#include <linux/poll.h>
+#include <linux/sched.h>
#include <xen/interface/xen.h>
#include <xen/events.h>
@@ -67,6 +69,8 @@
static int xen_mce_chrdev_open_count; /* #times opened */
static int xen_mce_chrdev_open_exclu; /* already open exclusive? */
+static DECLARE_WAIT_QUEUE_HEAD(xen_mce_chrdev_wait);
+
static int xen_mce_chrdev_open(struct inode *inode, struct file *file)
{
spin_lock(&xen_mce_chrdev_state_lock);
@@ -135,6 +139,16 @@
return err ? err : buf - ubuf;
}
+static unsigned int xen_mce_chrdev_poll(struct file *file, poll_table *wait)
+{
+ poll_wait(file, &xen_mce_chrdev_wait, wait);
+
+ if (xen_mcelog.next)
+ return POLLIN | POLLRDNORM;
+
+ return 0;
+}
+
static long xen_mce_chrdev_ioctl(struct file *f, unsigned int cmd,
unsigned long arg)
{
@@ -166,6 +180,7 @@
.open = xen_mce_chrdev_open,
.release = xen_mce_chrdev_release,
.read = xen_mce_chrdev_read,
+ .poll = xen_mce_chrdev_poll,
.unlocked_ioctl = xen_mce_chrdev_ioctl,
.llseek = no_llseek,
};
@@ -329,6 +344,9 @@
pr_err(XEN_MCELOG
"Failed to handle nonurgent mc_info queue.\n");
+ /* wake processes polling /dev/mcelog */
+ wake_up_interruptible(&xen_mce_chrdev_wait);
+
mutex_unlock(&mcelog_lock);
}
static DECLARE_WORK(xen_mce_work, xen_mce_work_fn);
