Re: [PATCH] xhci: use dma_alloc_coherent with fully cleared pages

[Tim Chen]

On Thu, 2015-02-19 at 17:05 +0200, Mathias Nyman wrote:
> On 19.02.2015 02:34, Tim Chen wrote:
> > 
> > Commit d92ef66c4f8f ("x86: make dma_alloc_coherent() return zeroed memory
> > if CMA is enabled") changed the dma_alloc_coherent page clearance from
> > using an __GFP_ZERO in page allocation to not setting the flag but doing
> > an explicit memory clear at the end.
> > 
> > However the memory clear only covered the memory size that
> > was requested, but may not be up to the full extent of the
> > last page, if the total pages returned exceed the
> > memory size requested.  This behavior has caused problem with XHCI
> > and caused it to hang:
> > 
> > kernel: xhci_hcd 0000:00:14.0: Stopped the command ring failed, maybe the host is dead
> > kernel: xhci_hcd 0000:00:14.0: Abort command ring failed
> > kernel: xhci_hcd 0000:00:14.0: HC died; cleaning up
> > kernel: xhci_hcd 0000:00:14.0: Error while assigning device slot ID
> > kernel: xhci_hcd 0000:00:14.0: Max number of devices this xHCI host supports is 64.
> > 
> > This patch reverts xhci the use the old behavior to avoid the hang.  XHCI should
> > do a proper fix to avoid this un-allocated memory.
> > 
> > Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx> # 3.16+
> > ---
> >  drivers/usb/host/xhci-mem.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> > index 5cb3d7a..39e7196 100644
> > --- a/drivers/usb/host/xhci-mem.c
> > +++ b/drivers/usb/host/xhci-mem.c
> > @@ -1658,7 +1658,7 @@ static int scratchpad_alloc(struct xhci_hcd *xhci, gfp_t flags)
> >  		goto fail_sp;
> >  
> >  	xhci->scratchpad->sp_array = dma_alloc_coherent(dev,
> > -				     num_sp * sizeof(u64),
> > +				     PAGE_ALIGN(num_sp * sizeof(u64)),
> >  				     &xhci->scratchpad->sp_dma, flags);
> >  	if (!xhci->scratchpad->sp_array)
> >  		goto fail_sp2;
> > 
> 
> Thanks for figuring out that the issue was in allocation of scratchpad memory.
> 
> Turns out we don't calculate the num_sp correctly in the first place, we didn't include
> the additional high order field of the max scratchpad buffers xhci tells we should reserve.
> I got a patch for this and will send it to forward to Greg once 3.20-rc1 is tagged
> 
> -Mathias

Confirmed that the patch:  xhci: Allocate correct amount of scratchpad buffers did resolve
the problem I've seen for XHCI.

Tim

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