Re: [Qemu-devel] [PATCH] qemu-char: another io_add_watch_poll fix

[Paolo Bonzini]

Il 10/04/2013 19:59, Amit Shah ha scritto:
> On (Wed) 10 Apr 2013 [15:23:27], Paolo Bonzini wrote:
>> After attaching the source, we have to remove the reference we hold
>> to it, because we do not hold anymore a pointer to the source.
>>
>> If we do not do this, removing the source will not finalize it and
>> will not drop the "real" I/O watch source.
>>
>> This showed up when backporting the new flow control patches to older
>> versions of QEMU that still used select.  The whole select then failed
>> with EBADF (poll instead will reporting POLLNVAL on a single pollfd)
>> and QEMU froze.
> 
> This patch doesn't apply directly to master, applies with some fuzz.
> However, this patch causes qemu freeze.  My testcase is:
> 
> Open chardev on host
> Write something to a virtserialport in guest
> Close chardev on host
> Keep writing to virtserialport in guest
> 
> When I apply the patch to the old qemu version with select, that
> starts working fine with the testcase above.

I cannot replicate the freeze.  The patch works on both old and new
versions of QEMU.  My testcases are:

1) on host, nc -l -p 12345
   on host, start qemu
   in guest, cat > /dev/vport0p1
   in guest, write something
   on host, close nc
   in guest, write something
   in guest, ^D and poweroff

2) on host, nc -l -p 12345
   on host, start qemu
   in guest, echo abc > /dev/vport0p1
   on host, close nc
   in guest, echo abc > /dev/vport0p1
   in guest, poweroff

> There's a slight difference in my old qemu tree, I have Hans's
> "virtio-console: Remove any pending watches on close" patch applied,
> which makes use of the tag obtained on adding the watch.  That patch
> hasn't found its way to master yet, but it should go in soon.

I don't have that patch in my (new) tree.  It's vanilla upstream QEMU.

Paolo