Re: [PATCH] migration/multifd: fix nullptr access in multifd_send_terminate_threads

[Juan Quintela <quintela@redhat.com>]

Zhimin Feng <fengzhimin1@huawei.com> wrote:
> If the multifd_send_threads is not created when migration is failed,
> multifd_save_cleanup would be called twice. In this senario, the
> multifd_send_state is accessed after it has been released, the result
> is that the source VM is crashing down.
>
> Here is the coredump stack:
>     Program received signal SIGSEGV, Segmentation fault.
>     0x00005629333a78ef in multifd_send_terminate_threads (err=err@entry=0x0) at migration/ram.c:1012
>     1012            MultiFDSendParams *p = &multifd_send_state->params[i];
>     #0  0x00005629333a78ef in multifd_send_terminate_threads (err=err@entry=0x0) at migration/ram.c:1012
>     #1  0x00005629333ab8a9 in multifd_save_cleanup () at migration/ram.c:1028
>     #2  0x00005629333abaea in multifd_new_send_channel_async (task=0x562935450e70, opaque=<optimized out>) at migration/ram.c:1202
>     #3  0x000056293373a562 in qio_task_complete (task=task@entry=0x562935450e70) at io/task.c:196
>     #4  0x000056293373a6e0 in qio_task_thread_result (opaque=0x562935450e70) at io/task.c:111
>     #5  0x00007f475d4d75a7 in g_idle_dispatch () from /usr/lib64/libglib-2.0.so.0
>     #6  0x00007f475d4da9a9 in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
>     #7  0x0000562933785b33 in glib_pollfds_poll () at util/main-loop.c:219
>     #8  os_host_main_loop_wait (timeout=<optimized out>) at util/main-loop.c:242
>     #9  main_loop_wait (nonblocking=nonblocking@entry=0) at util/main-loop.c:518
>     #10 0x00005629334c5acf in main_loop () at vl.c:1810
>     #11 0x000056293334d7bb in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4471
>
> If the multifd_send_threads is not created when migration is failed.
> In this senario, we don't call multifd_save_cleanup in multifd_new_send_channel_async.
>
> Signed-off-by: Zhimin Feng <fengzhimin1@huawei.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>