chardev: Don't attempt to unregister yank function more than once

tcp_chr_free_connection() can be called multiple times in succession, in which case the yank function will get as argument a NULL s->sioc that has been cleared by the previous tcp_chr_free_connection() call. This leads to an abort() at yank_unregister_function(). #0 __GI_raise (sig=6) at ../sysdeps/unix/sysv/linux/raise.c:51 #1 __GI_abort () at abort.c:79 #2 qtest_check_status (s=0x513000005600) at ../tests/qtest/libqtest.c:209 #3 qtest_wait_qemu (s=0x513000005600) at ../tests/qtest/libqtest.c:273 #4 qtest_kill_qemu (s=0x513000005600) at ../tests/qtest/libqtest.c:285 #5 kill_qemu_hook_func (s=0x513000005600) at ../tests/qtest/libqtest.c:294 #6 g_hook_list_invoke (hook_list=0x55ea9cc750c0 <abrt_hooks>, may_recurse=0) at ../glib/ghook.c:534 #7 sigabrt_handler (signo=6) at ../tests/qtest/libqtest.c:299 #8 <signal handler called> #9 __GI_raise (sig=6) at ../sysdeps/unix/sysv/linux/raise.c:51 #10 __GI_abort () at abort.c:79 #11 yank_unregister_function (instance=0x7fb26f2ea9a0, func=0x55ea9bcc0a10 <char_socket_yank_iochannel>, opaque=0x0) at ../util/yank.c:151 #12 tcp_chr_free_connection (chr=0x51300000ffc0) at ../chardev/char-socket.c:385 #13 tcp_chr_disconnect_locked (chr=0x51300000ffc0) at ../chardev/char-socket.c:477 #14 tcp_chr_disconnect (chr=0x51300000ffc0) at ../chardev/char-socket.c:495 #15 tcp_chr_hup (channel=0x514000000040, cond=G_IO_HUP, opaque=0x51300000ffc0) at ../chardev/char-socket.c:536 #16 qio_channel_fd_source_dispatch (source=0x50c0000b5fc0, callback=0x55ea9bcd6770 <tcp_chr_hup>, user_data=0x51300000ffc0) at ../io/channel-watch.c:84 #17 g_main_dispatch (context=0x50f000000040) at ../glib/gmain.c:3381 #18 g_main_context_dispatch (context=context@entry=0x50f000000040) at ../glib/gmain.c:4099 #19 g_main_context_iterate (context=0x50f000000040, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/gmain.c:4175 #20 g_main_loop_run (loop=0x502000055690) at ../glib/gmain.c:4373 Commit ebae6477dc ("chardev: check if the chardev is registered for yanking") seems to have encountered a similar issue, but checking s->registered_yank is not a complete solution because that flag pertains to the yank instance, not to each individual function. Skip the yank_unregister_function() in case s->sioc is already NULL, which indicates the last yank function was already removed. Signed-off-by: Fabiano Rosas <farosas@suse.de> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Message-id: 20260302092225.4088227-7-peter.maydell@linaro.org [PMM: rebased] Signed-off-by: Peter Maydell <peter.maydell@linaro.org>