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| author | Dr. David Alan Gilbert <dgilbert@redhat.com> | 2019-12-18 11:30:12 +0000 |
|---|---|---|
| committer | Gerd Hoffmann <kraxel@redhat.com> | 2020-01-13 14:05:46 +0100 |
| commit | 394642a8d3742c885e397d5bb5ee0ec40743cdc6 (patch) | |
| tree | ec6b5ea99341cffe2fc1fdd72cb9cacbd36dab94 /hw | |
| parent | 32187f3d902afdfa9f4d861d9612739d3391fdc3 (diff) | |
| download | qemu-394642a8d3742c885e397d5bb5ee0ec40743cdc6.zip | |
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>
Diffstat (limited to 'hw')
| -rw-r--r-- | hw/usb/redirect.c | 9 |
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; } |