Re: [PATCH for-next v2] RDMA/rxe: fix regression caused by recent patch

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Oct 30, 2020 at 12:45:54PM -0500, Bob Pearson wrote:
> >> +
> >> +	/* rdma_rxe never does real DMA but does rely on
> >> +	 * pinning user memory in MRs to avoid page faults
> >> +	 * in responder and completer tasklets. This code
> >> +	 * supplies a valid dma_mask from the underlying
> >> +	 * network device. It is never used but is checked.
> >> +	 */
> >> +	dev->dev.parent = rxe_dma_device(rxe);
> > 
> > Oh! This is another bug, the parent of an ib_device should never be
> > set to a net_device!! This is probably why we get all those mysterious
> > syzkaller faults :| Just leave it NULL
> > 
> >> +	dma_mask = *(dev->dev.parent->dma_mask);
> >> +	err = dma_coerce_mask_and_coherent(&dev->dev, dma_mask);
> > 
> > Why not use Parav's logic?
> > 
> > Jason
> 
> It's not the network device. It is the parent of the network device.
> On 64 bit machines it gives 0xffffffffffffffff as dma_mask.

No, it is some weird thing because network devices don't always have
physical device parents.

There is no relation between the netdevice RXE is running on and the
DMA mask to use for the dummy dma ops, AFAICT

> that should work on any architecture. If there is no reason to set
> dev.parent I can get rid of rxe_dma_device.

Please, that arrangement is causing bugs.

Jason