[Xen-devel] [Patch] fix xenfb_update_screen bogus rect

[Akio Takebe <takebe_akio@xxxxxxxxxxxxxx>]

Hi,

When I tested pvfb, I got the following warnings.
It seems to be caused by checking/setting info->dirty without dirty_lock.
We need to check/set info->dirty safely.

xenfb_update_screen bogus rect 2147483647 0 2147483647 0
 BUG: warning at 
/root/linux-2.6.18-xen.hg/drivers/xen/fbfront/xenfb.c:240/xenfb_update_screen()

 Call Trace:
  [<ffffffff8036920e>] xenfb_thread+0x19b/0x2be
  [<ffffffff8022730a>] try_to_wake_up+0x33b/0x34c
  [<ffffffff80225c3d>] __wake_up_common+0x3e/0x68
  [<ffffffff80241e20>] autoremove_wake_function+0x0/0x2e
  [<ffffffff80241a75>] keventd_create_kthread+0x0/0x61
  [<ffffffff80369073>] xenfb_thread+0x0/0x2be
  [<ffffffff80241a75>] keventd_create_kthread+0x0/0x61
  [<ffffffff80241ceb>] kthread+0xd4/0x109
  [<ffffffff8020afe0>] child_rip+0xa/0x12
  [<ffffffff80241a75>] keventd_create_kthread+0x0/0x61
  [<ffffffff8021477f>] xen_send_IPI_mask+0x0/0xf5
  [<ffffffff80241c17>] kthread+0x0/0x109
  [<ffffffff8020afd6>] child_rip+0x0/0x12


FYI, when I tested it, I used the following shell scripts on PV guest.
The above warnings occurred in /var/log/messages.
=======================
#!/bin/bash

while true
do
    date
done
=======================

The attached patch fixed this warnings.
How about it?

Signed-off-by: Akio Takebe <takebe_akio@xxxxxxxxxxxxxx>

Best Regards,

Akio Takebe

diff -r 83b71f4b5cb2 drivers/xen/fbfront/xenfb.c
--- a/drivers/xen/fbfront/xenfb.c       Tue Jan 20 13:28:35 2009 +0000
+++ b/drivers/xen/fbfront/xenfb.c       Tue Jan 27 20:09:58 2009 +0900
@@ -255,19 +255,36 @@
        }
        spin_unlock_irqrestore(&info->resize_lock, flags);
 }
+static int check_is_dirty(struct xenfb_info *info)
+{
+       int is_dirty;
+       unsigned long flags;
+       spin_lock_irqsave(&info->dirty_lock, flags);
+       is_dirty = info->dirty;
+       spin_unlock_irqrestore(&info->dirty_lock, flags);
+
+       return is_dirty;
+}
 
 static int xenfb_thread(void *data)
 {
        struct xenfb_info *info = data;
+       unsigned long flags;
+       int is_dirty;
 
        while (!kthread_should_stop()) {
                xenfb_handle_resize_dpy(info);
-               if (info->dirty) {
+               spin_lock_irqsave(&info->dirty_lock, flags);
+               is_dirty = info->dirty;
+               if (is_dirty) {
                        info->dirty = 0;
+                       spin_unlock_irqrestore(&info->dirty_lock, flags);
                        xenfb_update_screen(info);
+               } else {
+                       spin_unlock_irqrestore(&info->dirty_lock, flags);
                }
                wait_event_interruptible(info->wq,
-                       kthread_should_stop() || info->dirty);
+                       kthread_should_stop() || check_is_dirty(info));
                try_to_freeze();
        }
        return 0;

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