Re: [PATCH v3 6/6] freezer,sched: Rewrite core freezer logic

[Christian Borntraeger]

Am 26.09.22 um 12:55 schrieb Christian Borntraeger:
> Am 26.09.22 um 10:06 schrieb Christian Borntraeger:
> > Am 23.09.22 um 09:53 schrieb Christian Borntraeger:
> > > Am 23.09.22 um 09:21 schrieb Christian Borntraeger:
> > > > Peter,
> > > >
> > > > as a heads-up. This commit (bisected and verified) triggers a
> > > > regression in our KVM on s390x CI. The symptom is that a specific
> > > > testcase (start a guest with next kernel and a poky ramdisk,
> > > > then ssh via vsock into the guest and run the reboot command) now
> > > > takes much longer (300 instead of 20 seconds). From a first look
> > > > it seems that the sshd takes very long to end during shutdown
> > > > but I have not looked into that yet.
> > > > Any quick idea?
> > > >
> > > > Christian
> > >
> > > the sshd seems to hang in virtio-serial (not vsock).
> >
> > FWIW, sshd does not seem to hang, instead it seems to busy loop in
> > wait_port_writable calling into the scheduler over and over again.
>
> -#define TASK_FREEZABLE                 0x00002000
> +#define TASK_FREEZABLE                 0x00000000
>
> "Fixes" the issue. Just have to find out which of users is responsible.

So it seems that my initial test was not good enough.

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 9fa3c76a267f..e93df4f735fe 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -790,7 +790,7 @@ static int wait_port_writable(struct port *port, bool nonblock)
                if (nonblock)
                        return -EAGAIN;
 
-               ret = wait_event_freezable(port->waitqueue,
+               ret = wait_event_interruptible(port->waitqueue,
                                           !will_write_block(port));
                if (ret < 0)
                        return ret;

Does fix the problem.
My initial test was the following

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -790,10 +790,8 @@ static int wait_port_writable(struct port *port, bool nonblock)
                if (nonblock)
                        return -EAGAIN;
 
-               ret = wait_event_freezable(port->waitqueue,
+               wait_event(port->waitqueue,
                                           !will_write_block(port));
-               if (ret < 0)
-                       return ret;
        }
        /* Port got hot-unplugged. */
        if (!port->guest_connected)

and obviously it did not provide an exit path.