Re: [Qemu-devel] [5187] Use signalfd() to work around signal/select race

[Anthony Liguori <anthony@codemonkey.ws>]

Laurent Vivier wrote:
> Le mercredi 10 septembre 2008 à 15:45 +0000, Anthony Liguori a écrit :
>   
>> Revision: 5187
>>           http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5187
>> Author:   aliguori
>> Date:     2008-09-10 15:45:19 +0000 (Wed, 10 Sep 2008)
>>
>> Log Message:
>> -----------
>> Use signalfd() to work around signal/select race
>>     
>
> This commit breaks qemu-nbd:
>
> # ./qemu-nbd --port 1024 --persistent ../disk.qcow2 
> generates "Bus error" when I connect the client:
> # ./x86_64-softmmu/qemu-system-x86_64 -hda ../etch64.qcow2 -hdb
> nbd:localhost:1024
>
> * gdb output:
>
> Program received signal SIGBUS, Bus error.
> [Switching to Thread 0x7f3accdf76e0 (LWP 13146)]
> qemu_aio_wait () at block-raw-posix.c:541
> 541	        FD_SET(aio_sig_fd, &rdfds);
> (gdb) bt
> #0  qemu_aio_wait () at block-raw-posix.c:541
> #1  0x0000000000406245 in bdrv_read_em (bs=0x0,
> sector_num=140736764918416, 
>     buf=0x8000000000000000 <Address 0x8000000000000000 out of bounds>, 
>     nb_sectors=0) at block.c:1289
> #2  0x000000000040437a in nbd_trip (bs=0x622010, csock=8,
> size=6442450944, 
>     dev_offset=0, offset=0x7fffd4e13c78, readonly=false, 
>     data=0x7f3acccd5200 "�H\220м", data_size=1048576) at nbd.c:573
> #3  0x0000000000402d11 in main (argc=1, argv=0x1) at qemu-nbd.c:444
>   

That's because qemu-nbd isn't doing an qemu_aio_init().  There still 
appears to be an issue though because qemu_aio_wait() doesn't ever 
returning.  I'm looking into it right now.

Regards,

Anthony Liguori

> Laurent
>