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SubjectRe: [PATCH] xhci: Remove segments from radix tree on failed insert.
Hi,

On 10/17/2013 09:44 PM, Sarah Sharp wrote:
> If we're expanding a stream ring, we want to make sure we can add those
> ring segments to the radix tree that maps segments to ring pointers.
> Try the radix tree insert after the new ring segments have been allocated
> (the last segment in the new ring chunk will point to the first newly
> allocated segment), but before the new ring segments are linked into the
> old ring.
>
> If insert fails on any one segment, remove each segment from the radix
> tree, deallocate the new segments, and return. Otherwise, link the new
> segments into the tree.
>
> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
> ---
>
> Something like this.

Thanks for working on this.

> It's ugly, but it compiles. I haven't tested it.
> Hans, can you review and test this?

Reviewed, I've one small nitpick, see inline comments, other then that it looks
good, and I don't find it all that ugly :)

I've also run various tests and it seems to work as advertised (I've not
managed to trigger the error path though AFAIK).

Acked-by: Hans de Goede <hdegoede@redhat.com>

>
> Sarah Sharp
>
> drivers/usb/host/xhci-mem.c | 106 +++++++++++++++++++++++++++++++++-----------
> 1 file changed, 80 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
> index a455c56..6ce8d31 100644
> --- a/drivers/usb/host/xhci-mem.c
> +++ b/drivers/usb/host/xhci-mem.c
> @@ -180,53 +180,98 @@ static void xhci_link_rings(struct xhci_hcd *xhci, struct xhci_ring *ring,
> * extended systems (where the DMA address can be bigger than 32-bits),
> * if we allow the PCI dma mask to be bigger than 32-bits. So don't do that.
> */
> -static int xhci_update_stream_mapping(struct xhci_ring *ring, gfp_t mem_flags)
> +static int xhci_insert_segment_mapping(struct radix_tree_root *trb_address_map,
> + struct xhci_ring *ring,
> + struct xhci_segment *seg,
> + gfp_t mem_flags)
> {
> - struct xhci_segment *seg;
> unsigned long key;
> int ret;
>
> - if (WARN_ON_ONCE(ring->trb_address_map == NULL))
> + key = (unsigned long)(seg->dma >> TRB_SEGMENT_SHIFT);
> + /* Skip any segments that were already added. */
> + if (radix_tree_lookup(trb_address_map, key))
> return 0;
>
> - seg = ring->first_seg;
> - do {
> - key = (unsigned long)(seg->dma >> TRB_SEGMENT_SHIFT);
> - /* Skip any segments that were already added. */
> - if (radix_tree_lookup(ring->trb_address_map, key))
> - continue;
> + ret = radix_tree_maybe_preload(mem_flags);
> + if (ret)
> + return ret;
> + ret = radix_tree_insert(trb_address_map,
> + key, ring);
> + radix_tree_preload_end();
> + return ret;
> +}
>
> - ret = radix_tree_maybe_preload(mem_flags);
> - if (ret)
> - return ret;
> - ret = radix_tree_insert(ring->trb_address_map,
> - key, ring);
> - radix_tree_preload_end();
> +static void xhci_remove_segment_mapping(struct radix_tree_root *trb_address_map,
> + struct xhci_segment *seg)
> +{
> + unsigned long key;
> +
> + key = (unsigned long)(seg->dma >> TRB_SEGMENT_SHIFT);
> + if (radix_tree_lookup(trb_address_map, key))
> + radix_tree_delete(trb_address_map, key);
> +}
> +
> +static int xhci_update_stream_segment_mapping(
> + struct radix_tree_root *trb_address_map,
> + struct xhci_ring *ring,
> + struct xhci_segment *first_seg,
> + struct xhci_segment *last_seg,
> + gfp_t mem_flags)
> +{
> + struct xhci_segment *seg;
> + struct xhci_segment *failed_seg;
> + int ret;
> +
> + if (WARN_ON_ONCE(trb_address_map == NULL))
> + return 0;
> +
> + seg = first_seg;
> + do {
> + ret = xhci_insert_segment_mapping(trb_address_map,
> + ring, seg, mem_flags);
> if (ret)
> - return ret;
> + goto remove_streams;
> + if (seg == last_seg)
> + return 0;
> seg = seg->next;
> - } while (seg != ring->first_seg);
> + } while (seg != first_seg);

The while here tests for looping round, but that should never
happen, IMHO using do {} while (true); here would be more clear,
and also consistent with how the tear-down is done in the
error case in xhci_ring_expansion.

>
> return 0;
> +
> +remove_streams:
> + failed_seg = seg;
> + seg = first_seg;
> + do {
> + xhci_remove_segment_mapping(trb_address_map, seg);
> + if (seg == failed_seg)
> + return ret;
> + seg = seg->next;
> + } while (seg != first_seg);

And I would also prefer "} while (true};" here for the same reasons.

> +
> + return ret;
> }
>
> static void xhci_remove_stream_mapping(struct xhci_ring *ring)
> {
> struct xhci_segment *seg;
> - unsigned long key;
>
> if (WARN_ON_ONCE(ring->trb_address_map == NULL))
> return;
>
> seg = ring->first_seg;
> do {
> - key = (unsigned long)(seg->dma >> TRB_SEGMENT_SHIFT);
> - if (radix_tree_lookup(ring->trb_address_map, key))
> - radix_tree_delete(ring->trb_address_map, key);
> + xhci_remove_segment_mapping(ring->trb_address_map, seg);
> seg = seg->next;
> } while (seg != ring->first_seg);
> }
>
> +static int xhci_update_stream_mapping(struct xhci_ring *ring, gfp_t mem_flags)
> +{
> + return xhci_update_stream_segment_mapping(ring->trb_address_map, ring,
> + ring->first_seg, ring->last_seg, mem_flags);
> +}
> +
> /* XXX: Do we need the hcd structure in all these functions? */
> void xhci_ring_free(struct xhci_hcd *xhci, struct xhci_ring *ring)
> {
> @@ -429,16 +474,25 @@ int xhci_ring_expansion(struct xhci_hcd *xhci, struct xhci_ring *ring,
> if (ret)
> return -ENOMEM;
>
> + ret = xhci_update_stream_segment_mapping(ring->trb_address_map, ring,
> + first, last, flags);
> + if (ret) {
> + struct xhci_segment *next;
> + do {
> + next = first->next;
> + xhci_segment_free(xhci, first);
> + if (first == last)
> + break;
> + first = next;
> + } while (true);
> + return ret;
> + }
> +
> xhci_link_rings(xhci, ring, first, last, num_segs);
> xhci_dbg_trace(xhci, trace_xhci_dbg_ring_expansion,
> "ring expansion succeed, now has %d segments",
> ring->num_segs);
>
> - if (ring->type == TYPE_STREAM) {
> - ret = xhci_update_stream_mapping(ring, flags);
> - WARN_ON(ret); /* FIXME */
> - }
> -
> return 0;
> }
>
>

Regards,

Hans


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