[SLOF] [PATCH 3/3] virtio-serial: Do not close stdout on quiesce

Jordan Niethe jniethe5 at gmail.com
Mon Aug 28 11:37:36 AEST 2023

Commit 76fee95 ("slof: Only close stdout for virtio-serial devices")
says that commit cf28264 ("virtio-serial: Rework shutdown sequence")
fixed a hang. The problem was believed to be that it was necessary to
close stdout to shutdown the underlying virtio device.

Commit cf28264 ("virtio-serial: Rework shutdown sequence") closed stdout
on quiesce. This meant when prom_init() called write on stdout after
quiesce, there is a use after free so this is unreliable, and can also
hang (especially after reboots).

Quiescing is intended to put hardware into a safe state for the client
to take over. It is incorrect for SLOF to close ihandles that the client
could still be using, even after a quiesce.

Rather than closing the stdout device, all that needs to happen is to
ensure virtio-serial-shutdown gets called. On quiesce, close the virtio
device, but leave the stdout device itself open.

Commit 8174acd ("virtio-serial: Close device completely") handles reads
and writes as no-ops if the underlying virtio device is closed so there
is no problem with the client calling "write" on stdout after this, but
no output will be displayed.

Fixes: cf28264 ("virtio-serial: Rework shutdown sequence")
Debugged-by: Kautuk Consul <kconsul at linux.vnet.ibm.com>
Co-developed-by: Kautuk Consul <kconsul at linux.vnet.ibm.com>
Signed-off-by: Kautuk Consul <kconsul at linux.vnet.ibm.com>
Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
 board-qemu/slof/virtio-serial.fs | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/board-qemu/slof/virtio-serial.fs b/board-qemu/slof/virtio-serial.fs
index 41e2e04..54dacff 100644
--- a/board-qemu/slof/virtio-serial.fs
+++ b/board-qemu/slof/virtio-serial.fs
@@ -33,8 +33,6 @@ virtio-setup-vd VALUE virtiodev
 : virtio-serial-term-key?  virtiodev virtio-serial-haschar ;
 : virtio-serial-term-key   BEGIN virtio-serial-term-key? UNTIL virtiodev virtio-serial-getchar ;
-: virtio-serial-close-stdout s" stdout" get-chosen IF decode-int nip nip close-dev THEN ;
 \ Basic device initialization - which has only to be done once
 : init  ( -- )
 virtiodev virtio-serial-init drop
@@ -42,7 +40,7 @@ virtiodev virtio-serial-init drop
     \ Linux closes stdin at some point in prom_init(). This internally triggers a
     \ quiesce in SLOF. We must ensure stdout gets closed as well otherwise the
     \ device cannot be reset properly and the boot will hang.
-    ['] virtio-serial-close-stdout add-quiesce-xt
+    ['] shutdown add-quiesce-xt
 0 VALUE open-count
@@ -62,8 +60,8 @@ virtiodev virtio-serial-init drop
     open-count 0> IF
         open-count 1 - dup to open-count
         0= IF shutdown THEN
+        close
-    close
 : write ( addr len -- actual )

More information about the SLOF mailing list