From 394642a8d3742c885e397d5bb5ee0ec40743cdc6 Mon Sep 17 00:00:00 2001 From: "Dr. David Alan Gilbert" Date: Wed, 18 Dec 2019 11:30:12 +0000 Subject: 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 Message-Id: <20191218113012.13331-1-dgilbert@redhat.com> Signed-off-by: Gerd Hoffmann --- hw/usb/redirect.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'hw') diff --git a/hw/usb/redirect.c b/hw/usb/redirect.c index b5c1558..0461477 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; } -- cgit v1.1