Re: [Patch] fix xenfb_update_screen bogus rect

["Jan Beulich" <jbeulich@novell.com>]

Generally this looks okay (assuming it works), but couldn't the update_wanted
field then go away altogether?

Jan

>>> Akio Takebe <takebe_akio@jp.fujitsu.com> 28.01.09 08:31 >>>
Hi, Jan

Thank you for your review.
I remade it simpler.
But Just moving check-and-clear dirty flag to xenfb_update_screen(),
a guest with vcpu=1 could not boot.
It is caused by info->update_wanted = 0.
So I moved kthread_run() into XenbusStateConnected handling.
How about it?

Signed-off-by: Akio Takebe <takebe_akio@jp.fujitsu.com>

Best Regards,

Akio Takebe

Jan Beulich wrote:
> 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@jp.fujitsu.com> 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@jp.fujitsu.com>
> 
> Best Regards,
> 
> Akio Takebe
> 
>