Re: [PATCH v2 4/4] cxl/mem: Fix shutdown order

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Fri, 29 Sep 2023 16:52:06 -0700
Ira Weiny <ira.weiny@intel.com> wrote:

> Dan Williams wrote:
> > Ira reports that removing cxl_mock_mem causes a crash with the following
> > trace:
> > 
> >  BUG: kernel NULL pointer dereference, address: 0000000000000044
> >  [..]
> >  RIP: 0010:cxl_region_decode_reset+0x7f/0x180 [cxl_core]
> >  [..]
> >  Call Trace:
> >   <TASK>
> >   cxl_region_detach+0xe8/0x210 [cxl_core]
> >   cxl_decoder_kill_region+0x27/0x40 [cxl_core]
> >   cxld_unregister+0x29/0x40 [cxl_core]
> >   devres_release_all+0xb8/0x110
> >   device_unbind_cleanup+0xe/0x70
> >   device_release_driver_internal+0x1d2/0x210
> >   bus_remove_device+0xd7/0x150
> >   device_del+0x155/0x3e0
> >   device_unregister+0x13/0x60
> >   devm_release_action+0x4d/0x90
> >   ? __pfx_unregister_port+0x10/0x10 [cxl_core]
> >   delete_endpoint+0x121/0x130 [cxl_core]
> >   devres_release_all+0xb8/0x110
> >   device_unbind_cleanup+0xe/0x70
> >   device_release_driver_internal+0x1d2/0x210
> >   bus_remove_device+0xd7/0x150
> >   device_del+0x155/0x3e0
> >   ? lock_release+0x142/0x290
> >   cdev_device_del+0x15/0x50
> >   cxl_memdev_unregister+0x54/0x70 [cxl_core]
> > 
> > This crash is due to the clearing out the cxl_memdev's driver context
> > (@cxlds) before the subsystem is done with it. This is ultimately due to
> > the region(s), that this memdev is a member, being torn down and expecting
> > to be able to de-reference @cxlds, like here:
> > 
> > static int cxl_region_decode_reset(struct cxl_region *cxlr, int count)
> > ...
> >                 if (cxlds->rcd)
> >                         goto endpoint_reset;
> > ...
> > 
> > Fix it by keeping the driver context valid until memdev-device
> > unregistration, and subsequently the entire stack of related
> > dependencies, unwinds.
> > 
> > Fixes: 9cc238c7a526 ("cxl/pci: Introduce cdevm_file_operations")
> > Reported-by: Ira Weiny <ira.weiny@intel.com>  
> 
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> Tested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Thanks for cleaning up the whole area whilst fixing this.

Jonathan