Re: [Qemu-devel] [PATCH] vhost-user: return if no net clients found

[Chen Hanxiao]

在 2016-09-01 19:43:31，"Marc-André Lureau" <address@hidden> 写道：

Hi



On Thu, Sep 1, 2016 at 2:15 PM Chen Hanxiao <address@hidden> wrote:

From: Chen Hanxiao <address@hidden>

If we can't find a suitable net client, return directly.
Or we will got a segmentation fault.

Signed-off-by: Chen Hanxiao <address@hidden>
---
 net/vhost-user.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/vhost-user.c b/net/vhost-user.c
index b0595f8..fb96db7 100644
--- a/net/vhost-user.c
+++ b/net/vhost-user.c
@@ -210,6 +210,9 @@ static void net_vhost_user_event(void *opaque, int event)
                                           MAX_QUEUE_NUM);
     assert(queues < MAX_QUEUE_NUM);

+    if (queues < 1)
+        return;
+



qemu coding style has mandatory {} braces.


I don't understand what this patch fixes. even if queues == 0, there is not 
reason I can think of it would crash. Could you provide a backtrace?


A qemu-only reproducer would be really useful.


Hi, here is the backtrace:


#0  net_vhost_user_event (opaque=0x7fc2f6893be0, event=5) at 
net/vhost-user.c:196
#1  0x00007fc2f4ebfb2b in tcp_chr_disconnect (chr=0x7fc2f68cc400) at 
qemu-char.c:2837
#2  0x00007fc2f4ebfba9 in tcp_chr_sync_read (chr=0x7fc2f68cc400, buf=<optimized 
out>, len=<optimized out>) at qemu-char.c:2888
#3  0x00007fc2f4ec106d in qemu_chr_fe_read_all (s=0x7fc2f68cc400, 
address@hidden "", address@hidden) at qemu-char.c:264
#4  0x00007fc2f4f9a43a in net_vhost_user_watch (chan=<optimized out>, 
cond=<optimized out>, opaque=<optimized out>) at net/vhost-user.c:190
#5  0x00007fc2f321999a in g_main_context_dispatch () from 
/lib64/libglib-2.0.so.0
#6  0x00007fc2f4fd8fe8 in glib_pollfds_poll () at main-loop.c:209
#7  os_host_main_loop_wait (timeout=<optimized out>) at main-loop.c:254
#8  main_loop_wait (nonblocking=<optimized out>) at main-loop.c:503
#9  0x00007fc2f4dd7b1e in main_loop () at vl.c:1818
#10 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at 
vl.c:4394


Program received signal SIGSEGV, Segmentation fault.
net_vhost_user_event (opaque=0x7fc2f6893be0, event=5) at net/vhost-user.c:207
207    trace_vhost_user_event(s->chr->label, event);


Regards,
- Chen