Re: [Qemu-devel] apparently missing yet another notify_event()

[Michael Tokarev <mjt@tls.msk.ru>]

On 14.09.2012 18:47, Michael Tokarev wrote:
[]
>>
>>  qemu-kvm -nographic -kernel /boot/vmlinuz-$(uname -r) -append console=ttyS0 -serial pty
>>
>> This hangs till I send a char to the pty.
> 
> And it is even _more_ twisted than that.
> 
> It depends on the timing.  If I connect to the pty "too soon",
> it will not stall.
> 
> But if I wait for ~2 seconds or more before connecting, both
> qemu and qemu-kvm (and so current qemu/master too) will hang,
> requiring a keypress on the pty for the guest to start booting.

(qemu only in kvm mode).

I bisected this to:

commit 67c5322d7000fd105a926eec44bc1765b7d70bdd
Author: Anthony Liguori <aliguori@us.ibm.com>
Date:   Sun Apr 1 14:03:21 2012 -0500

    serial: fix retry logic

    I'm not sure if the retry logic has ever worked when not using FIFO mode.  I
    found this while writing a test case although code inspection confirms it is
    definitely broken.

    The TSR retry logic will never actually happen because it is guarded by an
    'if (s->tsr_rety > 0)' but this is the only place that can ever make the
    variable greater than zero.  That effectively makes the retry logic an 'if (0)'.

    I believe this is a typo and the intention was >= 0.  Once this is fixed though,
    I see double transmits with my test case.  This is because in the non FIFO
    case, serial_xmit may get invoked while LSR.THRE is still high because the
    character was processed but the retransmit timer was still active.

    We can handle this by simply checking for LSR.THRE and returning early.  It's
    possible that the FIFO paths also need some attention.

    Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
    Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

which is part of 1.1 development cycle.  Reverting this commit
from 1.2.0 fixes the issue there.

/mjt