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

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

Liu, Jinsong wrote:
> 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 
> 

Sorry, I update the patch a little, for spinlock to avoid deadlock.

Thanks,
Jinsong

====================
>From db6c0ac9372c6fbc3637ec4216830e7ee01b31aa Mon Sep 17 00:00:00 2001
From: Liu, Jinsong <jinsong.liu@xxxxxxxxx>
Date: Mon, 11 Jun 2012 19:21:24 +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 issue.

This patch also change the manipulation of mcelog_lock from
spin_lock_irqsave to spin_trylock to avoid deadlock, since
mcelog_lock is used at normal process context and
mce context (which is async exception context that could
not protected by spin_lock_irqsave). When fail to get spinlock,
mc_info would be transferred by hypervisor next time.

Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Liu, Jinsong <jinsong.liu@xxxxxxxxx>
---
 drivers/xen/mcelog.c |   38 +++++++++++++++++++++++++++++++-------
 1 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/drivers/xen/mcelog.c b/drivers/xen/mcelog.c
index 72e87d2..fac29e4 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 */
@@ -106,9 +108,19 @@ static ssize_t xen_mce_chrdev_read(struct file *filp, char 
__user *ubuf,
        unsigned num;
        int i, err;
 
+       /*
+        * copy_to_user might sleep and print a stack trace
+        * if it is executed in an atomic spinlock context
+        */
+       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;
 }
@@ -313,9 +325,21 @@ static int mc_queue_handle(uint32_t flags)
 static irqreturn_t xen_mce_interrupt(int irq, void *dev_id)
 {
        int err;
-       unsigned long tmp;
 
-       spin_lock_irqsave(&mcelog_lock, tmp);
+       /*
+        * mcelog_lock is used at normal process context and
+        * mce context (which is async exception context that could
+        * not protected by spin_lock_irqsave).
+        *
+        * use spin_trylock to avoid deadlock. When fail to get spinlock,
+        * mc_info would be transferred by hypervisor next time.
+        */
+       if (unlikely(!spin_trylock(&mcelog_lock))) {
+               pr_err(XEN_MCELOG
+                      "Failed to get mcelog_lock, mc_info would "
+                      "be transferred by hypervisor next time.\n");
+               return IRQ_NONE;
+       }
 
        /* urgent mc_info */
        err = mc_queue_handle(XEN_MC_URGENT);
@@ -330,7 +354,7 @@ static irqreturn_t xen_mce_interrupt(int irq, void *dev_id)
                pr_err(XEN_MCELOG
                       "Failed to handle nonurgent mc_info queue.\n");
 
-       spin_unlock_irqrestore(&mcelog_lock, tmp);
+       spin_unlock(&mcelog_lock);
 
        return IRQ_HANDLED;
 }
-- 
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

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