[Xen-devel] [PATCH] xen/mce: Add mutex lock and buffer to avoid sleep in atomic context

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

>From a9c5f29330a056291356b912816b5b2e0e061a30 Mon Sep 17 00:00:00 2001
From: Liu, Jinsong <jinsong.liu@xxxxxxxxx>
Date: Sat, 9 Jun 2012 00:56:46 +0800
Subject: [PATCH] xen/mce: Add mutex lock and buffer to avoid sleep in atomic 
context

copy_to_user might sleep and print a stack trace if it is executed
in an atomic spinlock context. This patch add a mutex lock and a
buffer to avoid the case.

Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Liu, Jinsong <jinsong.liu@xxxxxxxxx>
---
 drivers/xen/mcelog.c |   20 ++++++++++++++++----
 1 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/mcelog.c b/drivers/xen/mcelog.c
index 72e87d2..4046f01 100644
--- a/drivers/xen/mcelog.c
+++ b/drivers/xen/mcelog.c
@@ -56,12 +56,14 @@ static struct mcinfo_logical_cpu *g_physinfo;
 static uint32_t ncpus;
 
 static DEFINE_SPINLOCK(mcelog_lock);
+static DEFINE_MUTEX(xen_mce_chrdev_read_mutex);
 
 static struct xen_mce_log xen_mcelog = {
        .signature      = XEN_MCE_LOG_SIGNATURE,
        .len            = XEN_MCE_LOG_LEN,
        .recordlen      = sizeof(struct xen_mce),
 };
+static struct xen_mce_log xen_mcelog_u;
 
 static DEFINE_SPINLOCK(xen_mce_chrdev_state_lock);
 static int xen_mce_chrdev_open_count;  /* #times opened */
@@ -99,6 +101,10 @@ static int xen_mce_chrdev_release(struct inode *inode, 
struct file *file)
        return 0;
 }
 
+/*
+ * copy_to_user might sleep and print a stack trace
+ * if it is executed in an atomic spinlock context
+ */
 static ssize_t xen_mce_chrdev_read(struct file *filp, char __user *ubuf,
                                size_t usize, loff_t *off)
 {
@@ -106,9 +112,15 @@ static ssize_t xen_mce_chrdev_read(struct file *filp, char 
__user *ubuf,
        unsigned num;
        int i, err;
 
+       mutex_lock(&xen_mce_chrdev_read_mutex);
+
        spin_lock(&mcelog_lock);
+       memcpy(&xen_mcelog_u, &xen_mcelog, sizeof(struct xen_mce_log));
 
        num = xen_mcelog.next;
+       memset(xen_mcelog.entry, 0, num * sizeof(struct xen_mce));
+       xen_mcelog.next = 0;
+       spin_unlock(&mcelog_lock);
 
        /* Only supports full reads right now */
        err = -EINVAL;
@@ -117,20 +129,20 @@ static ssize_t xen_mce_chrdev_read(struct file *filp, 
char __user *ubuf,
 
        err = 0;
        for (i = 0; i < num; i++) {
-               struct xen_mce *m = &xen_mcelog.entry[i];
+               struct xen_mce *m = &xen_mcelog_u.entry[i];
 
                err |= copy_to_user(buf, m, sizeof(*m));
                buf += sizeof(*m);
        }
 
-       memset(xen_mcelog.entry, 0, num * sizeof(struct xen_mce));
-       xen_mcelog.next = 0;
+       memset(xen_mcelog_u.entry, 0, num * sizeof(struct xen_mce));
+       xen_mcelog_u.next = 0;
 
        if (err)
                err = -EFAULT;
 
 out:
-       spin_unlock(&mcelog_lock);
+       mutex_unlock(&xen_mce_chrdev_read_mutex);
 
        return err ? err : buf - ubuf;
 }
-- 
1.7.1

Attachment: 0001-xen-mce-Add-mutex-lock-and-buffer-to-avoid-sleep-in-.patch
Description: 0001-xen-mce-Add-mutex-lock-and-buffer-to-avoid-sleep-in-.patch

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel