diff options
authorDr. David Alan Gilbert <dgilbert@redhat.com>2019-12-18 11:30:12 +0000
committerGerd Hoffmann <kraxel@redhat.com>2020-01-13 14:05:46 +0100
commit394642a8d3742c885e397d5bb5ee0ec40743cdc6 (patch)
parent32187f3d902afdfa9f4d861d9612739d3391fdc3 (diff)
usbredir: Prevent recursion in usbredir_write
I've got a case where usbredir_write manages to call back into itself via spice; this patch causes the recursion to fail (0 bytes) the write; this seems to avoid the deadlock I was previously seeing. I can't say I fully understand the interaction of usbredir and spice; but there are a few similar guards in spice and usbredir to catch other cases especially onces also related to spice_server_char_device_wakeup This case seems to be triggered by repeated migration+repeated reconnection of the viewer; but my debugging suggests the migration finished before this hits. The backtrace of the hang looks like: reds_handle_ticket reds_handle_other_links reds_channel_do_link red_channel_connect spicevmc_connect usbredir_create_parser usbredirparser_do_write usbredir_write qemu_chr_fe_write qemu_chr_write qemu_chr_write_buffer spice_chr_write spice_server_char_device_wakeup red_char_device_wakeup red_char_device_write_to_device vmc_write usbredirparser_do_write usbredir_write qemu_chr_fe_write qemu_chr_write qemu_chr_write_buffer qemu_mutex_lock_impl and we fail as we lang through qemu_chr_write_buffer's lock twice. Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1752320 Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Message-Id: <20191218113012.13331-1-dgilbert@redhat.com> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
1 files changed, 9 insertions, 0 deletions
diff --git a/hw/usb/redirect.c b/hw/usb/redirect.c
index b5c1558687..04614778fe 100644
--- a/hw/usb/redirect.c
+++ b/hw/usb/redirect.c
@@ -114,6 +114,7 @@ struct USBRedirDevice {
CharBackend cs;
bool enable_streams;
bool suppress_remote_wake;
+ bool in_write;
uint8_t debug;
int32_t bootindex;
char *filter_str;
@@ -291,6 +292,13 @@ static int usbredir_write(void *priv, uint8_t *data, int count)
return 0;
+ /* Recursion check */
+ if (dev->in_write) {
+ DPRINTF("usbredir_write recursion\n");
+ return 0;
+ }
+ dev->in_write = true;
r = qemu_chr_fe_write(&dev->cs, data, count);
if (r < count) {
if (!dev->watch) {
@@ -301,6 +309,7 @@ static int usbredir_write(void *priv, uint8_t *data, int count)
r = 0;
+ dev->in_write = false;
return r;