On Mittwoch, 19. August 2020 08:29:39 CEST Geoffrey McRae wrote:
> This change registers a bottom handler to close the JACK client
> connection when a server shutdown signal is recieved. Without this
> libjack2 attempts to "clean up" old clients and causes a use after free
> segfault.
>
> Signed-off-by: Geoffrey McRae <ge...@hostfission.com>
> ---
Looks much better now, but ...
> audio/jackaudio.c | 29 ++++++++++++++++++++---------
> 1 file changed, 20 insertions(+), 9 deletions(-)
>
> diff --git a/audio/jackaudio.c b/audio/jackaudio.c
> index 72ed7c4929..b0da5cd00b 100644
> --- a/audio/jackaudio.c
> +++ b/audio/jackaudio.c
> @@ -25,6 +25,7 @@
> #include "qemu/osdep.h"
> #include "qemu/module.h"
> #include "qemu/atomic.h"
> +#include "qemu/main-loop.h"
> #include "qemu-common.h"
> #include "audio.h"
>
> @@ -63,6 +64,7 @@ typedef struct QJackClient {
> QJackState state;
> jack_client_t *client;
> jack_nframes_t freq;
> + QEMUBH *shutdown_bh;
>
> struct QJack *j;
> int nchannels;
> @@ -306,21 +308,27 @@ static int qjack_xrun(void *arg)
> return 0;
> }
>
> +static void qjack_shutdown_bh(void *opaque)
> +{
> + QJackClient *c = (QJackClient *)opaque;
> + qjack_client_fini(c);
> +}
> +
> static void qjack_shutdown(void *arg)
> {
> QJackClient *c = (QJackClient *)arg;
> - c->state = QJACK_STATE_SHUTDOWN;
> + c->state = QJACK_STATE_SHUTDOWN;
White space changes are not much embraced on high traffic projects BTW.
> + qemu_bh_schedule(c->shutdown_bh);
> }
>
> static void qjack_client_recover(QJackClient *c)
> {
> - if (c->state == QJACK_STATE_SHUTDOWN) {
> - qjack_client_fini(c);
> + if (c->state != QJACK_STATE_DISCONNECTED) {
> + return;
> }
>
> /* packets is used simply to throttle this */
> - if (c->state == QJACK_STATE_DISCONNECTED &&
> - c->packets % 100 == 0) {
> + if (c->packets % 100 == 0) {
>
> /* if enabled then attempt to recover */
> if (c->enabled) {
> @@ -417,6 +425,10 @@ static int qjack_client_init(QJackClient *c)
> options |= JackServerName;
> }
>
> + if (!c->shutdown_bh) {
> + c->shutdown_bh = qemu_bh_new(qjack_shutdown_bh, c);
> + }
> +
Where is qemu_bh_delete() ?
> c->client = jack_client_open(client_name, options, &status,
> c->opt->server_name);
>
> @@ -489,8 +501,6 @@ static int qjack_init_out(HWVoiceOut *hw, struct
> audsettings *as, QJackOut *jo = (QJackOut *)hw;
> Audiodev *dev = (Audiodev *)drv_opaque;
>
> - qjack_client_fini(&jo->c);
> -
> jo->c.out = true;
> jo->c.enabled = false;
> jo->c.nchannels = as->nchannels;
> @@ -525,8 +535,6 @@ static int qjack_init_in(HWVoiceIn *hw, struct
> audsettings *as, QJackIn *ji = (QJackIn *)hw;
> Audiodev *dev = (Audiodev *)drv_opaque;
>
> - qjack_client_fini(&ji->c);
> -
> ji->c.out = false;
> ji->c.enabled = false;
> ji->c.nchannels = as->nchannels;
> @@ -557,6 +565,8 @@ static int qjack_init_in(HWVoiceIn *hw, struct
> audsettings *as,
>
> static void qjack_client_fini(QJackClient *c)
> {
> + qemu_bh_cancel(c->shutdown_bh);
> +
Looks like a potential race. Quote from the API doc of qemu_bh_cancel():
"While cancellation itself is also wait-free and thread-safe, it can of
course race with the loop that executes bottom halves unless you are
holding the iothread mutex. This makes it mostly useless if you are
not
holding the mutex."
> switch (c->state) {
> case QJACK_STATE_RUNNING:
> jack_deactivate(c->client);
> @@ -564,6 +574,7 @@ static void qjack_client_fini(QJackClient *c)
>
> case QJACK_STATE_SHUTDOWN:
> jack_client_close(c->client);
> + c->client = NULL;
> /* fallthrough */
>
> case QJACK_STATE_DISCONNECTED:
Best regards,
Christian Schoenebeck
