[Qemu-devel] "make check -j4" hangs (was: Re: chardev/char-socket: add POLLHUP handler)

[Thomas Huth <thuth@redhat.com>]

On 30.01.2018 20:49, Paolo Bonzini wrote:
> On 25/01/2018 08:51, Klim Kireev wrote:
>> The following behavior was observed for QEMU configured by libvirt
>> to use guest agent as usual for the guests without virtio-serial
>> driver (Windows or the guest remaining in BIOS stage).
>>
>> In QEMU on first connect to listen character device socket
>> the listen socket is removed from poll just after the accept().
>> virtio_serial_guest_ready() returns 0 and the descriptor
>> of the connected Unix socket is removed from poll and it will
>> not be present in poll() until the guest will initialize the driver
>> and change the state of the serial to "guest connected".
>>
>> In libvirt connect() to guest agent is performed on restart and
>> is run under VM state lock. Connect() is blocking and can
>> wait forever.
>> In this case libvirt can not perform ANY operation on that VM.
>>
>> The bug can be easily reproduced this way:
>>
>> Terminal 1:
>> qemu-system-x86_64 -m 512 -device pci-serial,chardev=serial1 -chardev socket,id=serial1,path=/tmp/console.sock,server,nowait
>> (virtio-serial and isa-serial also fit)
>>
>> Terminal 2:
>> minicom -D unix\#/tmp/console.sock
>> (type something and press enter)
>> C-a x (to exit)
>>
>> Do 3 times:
>> minicom -D unix\#/tmp/console.sock
>> C-a x
>>
>> It needs 4 connections, because the first one is accepted by QEMU, then two are queued by
>> the kernel, and the 4th blocks.
>>
>> The problem is that QEMU doesn't add a read watcher after succesful read
>> until the guest device wants to acquire recieved data, so
>> I propose to install a separate pullhup watcher regardless of
>> whether the device waits for data or not.
>>
>> Signed-off-by: Klim Kireev <klim.kireev@virtuozzo.com>
>> ---
>> Changelog:
>> v2: Remove timer as a redundant feature
>>
>> v3: Remove read call and return G_SOURCE_REMOVE
>>
>> v4: Move to GSource API
>>
>> v5: Fix git typos 
>>
>>  chardev/char-socket.c | 22 ++++++++++++++++++++++
>>  1 file changed, 22 insertions(+)
>>
>> diff --git a/chardev/char-socket.c b/chardev/char-socket.c
>> index 77cdf487eb..a340af6cd3 100644
>> --- a/chardev/char-socket.c
>> +++ b/chardev/char-socket.c
>> @@ -42,6 +42,7 @@ typedef struct {
>>      QIOChannel *ioc; /* Client I/O channel */
>>      QIOChannelSocket *sioc; /* Client master channel */
>>      QIONetListener *listener;
>> +    GSource *hup_source;
>>      QCryptoTLSCreds *tls_creds;
>>      int connected;
>>      int max_size;
>> @@ -352,6 +353,12 @@ static void tcp_chr_free_connection(Chardev *chr)
>>          s->read_msgfds_num = 0;
>>      }
>>  
>> +    if (s->hup_source != NULL) {
>> +        g_source_destroy(s->hup_source);
>> +        g_source_unref(s->hup_source);
>> +        s->hup_source = NULL;
>> +    }
>> +
>>      tcp_set_msgfds(chr, NULL, 0);
>>      remove_fd_in_watch(chr);
>>      object_unref(OBJECT(s->sioc));
>> @@ -455,6 +462,15 @@ static gboolean tcp_chr_read(QIOChannel *chan, GIOCondition cond, void *opaque)
>>      return TRUE;
>>  }
>>  
>> +static gboolean tcp_chr_hup(QIOChannel *channel,
>> +                               GIOCondition cond,
>> +                               void *opaque)
>> +{
>> +    Chardev *chr = CHARDEV(opaque);
>> +    tcp_chr_disconnect(chr);
>> +    return G_SOURCE_REMOVE;
>> +}
>> +
>>  static int tcp_chr_sync_read(Chardev *chr, const uint8_t *buf, int len)
>>  {
>>      SocketChardev *s = SOCKET_CHARDEV(chr);
>> @@ -528,6 +544,12 @@ static void tcp_chr_connect(void *opaque)
>>                                             tcp_chr_read,
>>                                             chr, chr->gcontext);
>>      }
>> +
>> +    s->hup_source = qio_channel_create_watch(s->ioc, G_IO_HUP);
>> +    g_source_set_callback(s->hup_source, (GSourceFunc)tcp_chr_hup,
>> +                          chr, NULL);
>> +    g_source_attach(s->hup_source, chr->gcontext);
>> +
>>      qemu_chr_be_event(chr, CHR_EVENT_OPENED);
>>  }
>>  
>>
> 
> Queued, thanks.

 Hi!

I'm currently facing some issues with "make check -j4" (i.e. running the
tests in parallel). Git bisect blames this commit - though I'm not sure
whether this is really the right one ... Starting with this commit, I
saw hangs in test-filter-redirector, but git master rather seems to hang
with vhost-user-test instead.
Stefan also had issues with "make check -j4" today, so it's apparently
not only me ... can somebody else reproduce the problem with the git
master branch?

 Thomas