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

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

This looks bogus to me. check_is_dirty() definitely isn't needed - if at all, a
memory read barrier may need to be added, but since kthread_should_stop()
is a function call even that ought to be unnecessary.

I also think the other change is more involved than it needs to be - it'd be
much simpler to let xenfb_update_screen() check-and-clear the dirty flag
along with reading the other fields, and bail if the flag was clear.

Jan

>>> Akio Takebe <takebe_akio@xxxxxxxxxxxxxx> 27.01.09 03:58 >>>
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


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