Re: [Qemu-devel] [PATCH] qemu_opt_foreach: Fix crasher

[Marc-André Lureau]

Hi

On Tue, Aug 16, 2016 at 7:18 PM Michal Privoznik <address@hidden>
wrote:

> Program terminated with signal SIGSEGV, Segmentation fault.
> #0  0x000055baf6ab4adc in qemu_opt_foreach (opts=0x0, func=0x55baf696b650
> <net_vhost_chardev_opts>, opaque=0x7ffc51368c00, errp=0x7ffc51368e48) at
> util/qemu-option.c:617
> 617         QTAILQ_FOREACH(opt, &opts->head, next) {
> [Current thread is 1 (Thread 0x7f1d4970bb40 (LWP 6603))]
> (gdb) bt
> #0  0x000055baf6ab4adc in qemu_opt_foreach (opts=0x0, func=0x55baf696b650
> <net_vhost_chardev_opts>, opaque=0x7ffc51368c00, errp=0x7ffc51368e48) at
> util/qemu-option.c:617
> #1  0x000055baf696b7da in net_vhost_parse_chardev (opts=0x55baf8ff9260,
> errp=0x7ffc51368e48) at net/vhost-user.c:314
> #2  0x000055baf696b985 in net_init_vhost_user (netdev=0x55baf8ff9250,
> name=0x55baf879d270 "hostnet2", peer=0x0, errp=0x7ffc51368e48) at
> net/vhost-user.c:360
> #3  0x000055baf6960216 in net_client_init1 (object=0x55baf8ff9250,
> is_netdev=true, errp=0x7ffc51368e48) at net/net.c:1051
> #4  0x000055baf6960518 in net_client_init (opts=0x55baf776e7e0,
> is_netdev=true, errp=0x7ffc51368f00) at net/net.c:1108
> #5  0x000055baf696083f in netdev_add (opts=0x55baf776e7e0,
> errp=0x7ffc51368f00) at net/net.c:1186
> #6  0x000055baf69608c7 in qmp_netdev_add (qdict=0x55baf7afaf60,
> ret=0x7ffc51368f50, errp=0x7ffc51368f48) at net/net.c:1205
> #7  0x000055baf6622135 in handle_qmp_command (parser=0x55baf77fb590,
> tokens=0x7f1d24011960) at /path/to/qemu.git/monitor.c:3978
> #8  0x000055baf6a9d099 in json_message_process_token
> (lexer=0x55baf77fb598, input=0x55baf75acd20, type=JSON_RCURLY, x=113, y=19)
> at qobject/json-streamer.c:105
> #9  0x000055baf6abf7aa in json_lexer_feed_char (lexer=0x55baf77fb598,
> ch=125 '}', flush=false) at qobject/json-lexer.c:319
> #10 0x000055baf6abf8f2 in json_lexer_feed (lexer=0x55baf77fb598,
> buffer=0x7ffc51369170 "}R\204\367\272U", size=1) at qobject/json-lexer.c:369
> #11 0x000055baf6a9d13c in json_message_parser_feed (parser=0x55baf77fb590,
> buffer=0x7ffc51369170 "}R\204\367\272U", size=1) at
> qobject/json-streamer.c:124
> #12 0x000055baf66221f7 in monitor_qmp_read (opaque=0x55baf77fb530,
> buf=0x7ffc51369170 "}R\204\367\272U", size=1) at
> /path/to/qemu.git/monitor.c:3994
> #13 0x000055baf6757014 in qemu_chr_be_write_impl (s=0x55baf7610a40,
> buf=0x7ffc51369170 "}R\204\367\272U", len=1) at qemu-char.c:387
> #14 0x000055baf6757076 in qemu_chr_be_write (s=0x55baf7610a40,
> buf=0x7ffc51369170 "}R\204\367\272U", len=1) at qemu-char.c:399
> #15 0x000055baf675b3b0 in tcp_chr_read (chan=0x55baf90244b0, cond=G_IO_IN,
> opaque=0x55baf7610a40) at qemu-char.c:2927
> #16 0x000055baf6a5d655 in qio_channel_fd_source_dispatch
> (source=0x55baf7610df0, callback=0x55baf675b25a <tcp_chr_read>,
> user_data=0x55baf7610a40) at io/channel-watch.c:84
> #17 0x00007f1d3e80cbbd in g_main_context_dispatch () from
> /usr/lib64/libglib-2.0.so.0
> #18 0x000055baf69d3720 in glib_pollfds_poll () at main-loop.c:213
> #19 0x000055baf69d37fd in os_host_main_loop_wait (timeout=126000000) at
> main-loop.c:258
> #20 0x000055baf69d38ad in main_loop_wait (nonblocking=0) at main-loop.c:506
> #21 0x000055baf676587b in main_loop () at vl.c:1908
> #22 0x000055baf676d3bf in main (argc=101, argv=0x7ffc5136a6c8,
> envp=0x7ffc5136a9f8) at vl.c:4604
> (gdb) p opts
> $1 = (QemuOpts *) 0x0
>
> The crash occurred when I tried to attach vhost-user net:
>
>
> {"execute":"chardev-add","arguments":{"id":"charnet2","backend":{"type":"socket","data":{"addr":{"type":"unix","data":{"path":"/var/run/openvswitch/vhost-user1"}},"wait":false,"server":false}}},"id":"libvirt-19"}
> {"return": {}, "id": "libvirt-19"}
>
> {"execute":"netdev_add","arguments":{"type":"vhost-user","chardev":"charnet2","id":"hostnet2"},"id":"libvirt-20"}
>
> 2016-08-16 14:52:18.274+0000: 6456: error : qemuMonitorIORead:586 : Unable
> to read from monitor: Connection reset by peer
>
>
fwiw, this crash can be reproduced with 2.5: it's not a regression. Imho,
it shouldn't prevent or delay 2.7.


>
> The solution is to teach qemu_opt_foreach() to take a shortcut if
> @opts is NULL.
>
> Signed-off-by: Michal Privoznik <address@hidden>
> ---
>
> Even after this patch I'm still unable to attach vhost-user:
>
> {"id": "libvirt-20", "error": {"class": "GenericError", "desc": "chardev
> \"charnet2\" is not a unix socket"}}
>
> But at least, qemu does not crash anymore.
>
>  util/qemu-option.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/util/qemu-option.c b/util/qemu-option.c
> index 3467dc2..78be7e1 100644
> --- a/util/qemu-option.c
> +++ b/util/qemu-option.c
> @@ -614,6 +614,11 @@ int qemu_opt_foreach(QemuOpts *opts,
> qemu_opt_loopfunc func, void *opaque,
>      QemuOpt *opt;
>      int rc;
>
> +    if (!opts) {
> +        /* Done, trivially. */
> +        return 0;
> +    }
> +
>      QTAILQ_FOREACH(opt, &opts->head, next) {
>          rc = func(opaque, opt->name, opt->str, errp);
>          if (rc) {
> --
> 2.8.4
>
>
> --
Marc-André Lureau