qemu-kvm/SOURCES/kvm-usbredir-Prevent-recursion-in-usbredir_write.patch

107 lines
3.2 KiB
Diff

From 8f6311159977b8ee4b78172caa411d3cee4d2ae5 Mon Sep 17 00:00:00 2001
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Date: Tue, 14 Jan 2020 20:23:30 +0000
Subject: [PATCH 4/5] usbredir: Prevent recursion in usbredir_write
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
RH-Author: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-id: <20200114202331.51831-2-dgilbert@redhat.com>
Patchwork-id: 93344
O-Subject: [RHEL-AV-8.2.0 qemu-kvm PATCH 1/2] usbredir: Prevent recursion in usbredir_write
Bugzilla: 1790844
RH-Acked-by: Peter Xu <peterx@redhat.com>
RH-Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>
RH-Acked-by: Gerd Hoffmann <kraxel@redhat.com>
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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 land 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>
(cherry picked from commit 394642a8d3742c885e397d5bb5ee0ec40743cdc6)
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
hw/usb/redirect.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/hw/usb/redirect.c b/hw/usb/redirect.c
index e0f5ca6..97f2c3a 100644
--- a/hw/usb/redirect.c
+++ b/hw/usb/redirect.c
@@ -113,6 +113,7 @@ struct USBRedirDevice {
/* Properties */
CharBackend cs;
bool enable_streams;
+ bool in_write;
uint8_t debug;
int32_t bootindex;
char *filter_str;
@@ -290,6 +291,13 @@ 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) {
@@ -300,6 +308,7 @@ static int usbredir_write(void *priv, uint8_t *data, int count)
r = 0;
}
}
+ dev->in_write = false;
return r;
}
--
1.8.3.1