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Re: [PATCH] udevProcessCSS: fix segfault



On Tue, Sep 22, 2020 at 10:45:09AM +0200, Boris Fiuczynski wrote:
> On 9/22/20 8:26 AM, Erik Skultety wrote:
> > On Mon, Sep 21, 2020 at 07:06:32PM +0200, Marc Hartmayer wrote:
> > > Don't process subchannel devices where `def->driver` is not set. This
> > > fixes the following segfault:
> > > 
> > > Thread 21 "nodedev-init" received signal SIGSEGV, Segmentation fault.
> > > [Switching to Thread 0x3ffb08fc910 (LWP 64303)]
> > > (gdb) bt
> > >   #0  0x000003fffd1272b4 in __strcmp_vx () at /lib64/libc.so.6
> > >   #1  0x000003ffc260c3a8 in udevProcessCSS (device=0x3ff9018d130, def=0x3ff90194a90)
> > >   #2  0x000003ffc260cb78 in udevGetDeviceDetails (device=0x3ff9018d130, def=0x3ff90194a90)
> > >   #3  0x000003ffc260d126 in udevAddOneDevice (device=0x3ff9018d130)
> > >   #4  0x000003ffc260d414 in udevProcessDeviceListEntry (udev=0x3ffa810d800, list_entry=0x3ff90001990)
> > >   #5  0x000003ffc260d638 in udevEnumerateDevices (udev=0x3ffa810d800)
> > >   #6  0x000003ffc260e08e in nodeStateInitializeEnumerate (opaque=0x3ffa810d800)
> > >   #7  0x000003fffdaa14b6 in virThreadHelper (data=0x3ffa810df00)
> > >   #8  0x000003fffc309ed6 in start_thread ()
> > >   #9  0x000003fffd185e66 in thread_start ()
> > > (gdb) p *def
> > > $2 = {
> > >    name = 0x0,
> > >    sysfs_path = 0x3ff90198e80 "/sys/devices/css0/0.0.ff40",
> > 
> > Okay, this patch fixes the segfault. However, if ^this generated it because the
> > driver name is not set, how do we even get to the resulting device tree as
> > outlined in 05e6cdafa6e0?
> > 
> > +- css_0_0_003a
> >      |
> >      +- ccw_0_0_1a2b
> >          |
> >          +- scsi_host0
> > 
> > What kind of CSS device is the one causing the error? If we skip this CSS
> > device, we don't generate a name for it and don't put it in the list, so I'm
> > quite puzzled on what I missed in the IBM document and thus in the review
> > process.
> > 
> > FWIW:
> > Reviewed-by: Erik Skultety <eskultet redhat com>
> > 
> 
> Erik,
> for whatever reason Marcs system does not have the subchannel device driver
> "chsc_subchannel" loaded. Therefore the subchannel is not bound to any
> driver and by the way this would be a filtered device since we want to show
> the users only io_subchannel and vfio_ccw subchannels.
> The tree above shows a subchannel bound to the io_subchannel device driver.
> Maybe it helps you to see a full example of how it looks on my system:

Oh, it would have been a different driver anyway - impossible to spot just from
the address :).
Yeah, the tree dump makes it much clearer, thanks, I pushed the patch.

Erik


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