Re: [Xen-devel] xenstored crashes with SIGSEGV

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-12-16 at 10:45 +0000, Ian Campbell wrote:
> On Mon, 2014-12-15 at 23:29 +0100, Philipp Hahn wrote:
> > > I notice in your bugzilla (for a different occurrence, I think):
> > >> [2090451.721705] univention-conf[2512]: segfault at ff00000000 ip 
> > >> 000000000045e238 sp 00007ffff68dfa30 error 6 in python2.6[400000+21e000]
> > > 
> > > Which appears to have faulted access 0xff000000000 too. It looks like
> > > this process is a python thing, it's nothing to do with xenstored I
> > > assume?
> > 
> > Yes, that's one univention-config, which is completely independent of
> > xen(stored).
> > 
> > > It seems rather coincidental that it should be accessing the 
> > > same sort of address and be faulting.
> > 
> > Yes, good catch. I'll have another look at those core dumps.
> 
> With this in mind, please can you confirm what model of machines you've
> seen this on, and in particular whether they are all the same class of
> machine or whether they are significantly different.
> 
> The reason being that randomly placed 0xff values in a field of 0x00
> could possibly indicate hardware (e.g. a GPU) DMAing over the wrong
> memory pages.

Thanks for giving me access to the core files. This is very suspicious:
(gdb) frame 2
#2  0x000000000040a348 in tdb_open_ex (name=0x1941fb0 
"/var/lib/xenstored/tdb.0x1935bb0", hash_size=<value optimized out>, 
tdb_flags=0, open_flags=<value optimized out>, mode=<value optimized out>, 
    log_fn=0x4093b0 <null_log_fn>, hash_fn=<value optimized out>) at tdb.c:1958
1958            SAFE_FREE(tdb->locked);

(gdb) x/96x tdb
0x1921270:      0x00000000      0x00000000      0x00000000      0x00000000
0x1921280:      0x0000001f      0x000000ff      0x0000ff00      0x000000ff
0x1921290:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x19212a0:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x19212b0:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x19212c0:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x19212d0:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x19212e0:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x19212f0:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x1921300:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x1921310:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x1921320:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x1921330:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x1921340:      0x00000000      0x00000000      0x0000ff00      0x000000ff
0x1921350:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x1921360:      0x00000000      0x000000ff      0x0000ff00      0x000000ff
0x1921370:      0x004093b0      0x00000000      0x004092f0      0x00000000
0x1921380:      0x00000002      0x00000000      0x00000091      0x00000000
0x1921390:      0x0193de70      0x00000000      0x01963600      0x00000000
0x19213a0:      0x00000000      0x00000000      0x0193fbb0      0x00000000
0x19213b0:      0x00000000      0x00000000      0x00000000      0x00000000
0x19213c0:      0x00405870      0x00000000      0x0040e3e0      0x00000000
0x19213d0:      0x00000038      0x00000000      0xe814ec70      0x6f2f6567
0x19213e0:      0x01963650      0x00000000      0x0193dec0      0x00000000

Something has clearly done a number on the ram of this process.
0x1921270 through 0x192136f is 256 bytes...

Since it appears to be happening to other processes too I would hazard
that this is not a xenstored issue.

Ian.


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