by Jan Beulich

[permalink] [raw]

Subject: Re: [Xen-devel] [PATCH 2/2] xen/blkfront: Add BUG_ON to deal with misbehaving backends.

>>> On 11.06.12 at 20:52, Konrad Rzeszutek Wilk <[email protected]> wrote:
> From: Konrad Rzeszutek Wilk <[email protected]>
> Date: Fri, 25 May 2012 17:34:51 -0400
> Subject: [PATCH] xen/blkfront: Add WARN to deal with misbehaving backends.
>
> Part of the ring structure is the 'id' field which is under
> control of the frontend. The frontend stamps it with "some"
> value (this some in this implementation being a value less
> than BLK_RING_SIZE), and when it gets a response expects
> said value to be in the response structure. We have a check
> for the id field when spolling new requests but not when
> de-spolling responses.
>
> We also add an extra check in add_id_to_freelist to make
> sure that the 'struct request' was not NULL - as we cannot
> pass a NULL to __blk_end_request_all, otherwise that crashes
> (and all the operations that the response is dealing with
> end up with __blk_end_request_all).
>
> Lastly we also print the name of the operation that failed.
>
> [v1: s/BUG/WARN/ suggested by Stefano]
> [v2: Add extra check in add_id_to_freelist]
> [v3: Redid op_name per Jan's suggestion]
> [v4: add const * and add WARN on failure returns]
> Acked-by: Stefano Stabellini <[email protected]>
> Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>

Acked-by: Jan Beulich <[email protected]>

> ---
> drivers/block/xen-blkfront.c | 58 +++++++++++++++++++++++++++++++++--------
> 1 files changed, 46 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 60eed4b..e4fb337 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -141,14 +141,36 @@ static int get_id_from_freelist(struct blkfront_info
> *info)
> return free;
> }
>
> -static void add_id_to_freelist(struct blkfront_info *info,
> +static int add_id_to_freelist(struct blkfront_info *info,
> unsigned long id)
> {
> + if (info->shadow[id].req.u.rw.id != id)
> + return -EINVAL;
> + if (info->shadow[id].request == NULL)
> + return -EINVAL;
> info->shadow[id].req.u.rw.id = info->shadow_free;
> info->shadow[id].request = NULL;
> info->shadow_free = id;
> + return 0;
> }
>
> +static const char *op_name(int op)
> +{
> + static const char *const names[] = {
> + [BLKIF_OP_READ] = "read",
> + [BLKIF_OP_WRITE] = "write",
> + [BLKIF_OP_WRITE_BARRIER] = "barrier",
> + [BLKIF_OP_FLUSH_DISKCACHE] = "flush",
> + [BLKIF_OP_DISCARD] = "discard" };
> +
> + if (op < 0 || op >= ARRAY_SIZE(names))
> + return "unknown";
> +
> + if (!names[op])
> + return "reserved";
> +
> + return names[op];
> +}
> static int xlbd_reserve_minors(unsigned int minor, unsigned int nr)
> {
> unsigned int end = minor + nr;
> @@ -746,20 +768,36 @@ static irqreturn_t blkif_interrupt(int irq, void
> *dev_id)
>
> bret = RING_GET_RESPONSE(&info->ring, i);
> id = bret->id;
> + /*
> + * The backend has messed up and given us an id that we would
> + * never have given to it (we stamp it up to BLK_RING_SIZE -
> + * look in get_id_from_freelist.
> + */
> + if (id >= BLK_RING_SIZE) {
> + WARN(1, "%s: response to %s has incorrect id (%ld)\n",
> + info->gd->disk_name, op_name(bret->operation), id);
> + /* We can't safely get the 'struct request' as
> + * the id is busted. */
> + continue;
> + }
> req = info->shadow[id].request;
>
> if (bret->operation != BLKIF_OP_DISCARD)
> blkif_completion(&info->shadow[id]);
>
> - add_id_to_freelist(info, id);
> + if (add_id_to_freelist(info, id)) {
> + WARN(1, "%s: response to %s (id %ld) couldn't be recycled!\n",
> + info->gd->disk_name, op_name(bret->operation), id);
> + continue;
> + }
>
> error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
> switch (bret->operation) {
> case BLKIF_OP_DISCARD:
> if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
> struct request_queue *rq = info->rq;
> - printk(KERN_WARNING "blkfront: %s: discard op failed\n",
> - info->gd->disk_name);
> + printk(KERN_WARNING "blkfront: %s: %s op failed\n",
> + info->gd->disk_name, op_name(bret->operation));
> error = -EOPNOTSUPP;
> info->feature_discard = 0;
> info->feature_secdiscard = 0;
> @@ -771,18 +809,14 @@ static irqreturn_t blkif_interrupt(int irq, void
> *dev_id)
> case BLKIF_OP_FLUSH_DISKCACHE:
> case BLKIF_OP_WRITE_BARRIER:
> if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
> - printk(KERN_WARNING "blkfront: %s: write %s op failed\n",
> - info->flush_op == BLKIF_OP_WRITE_BARRIER ?
> - "barrier" : "flush disk cache",
> - info->gd->disk_name);
> + printk(KERN_WARNING "blkfront: %s: %s op failed\n",
> + info->gd->disk_name, op_name(bret->operation));
> error = -EOPNOTSUPP;
> }
> if (unlikely(bret->status == BLKIF_RSP_ERROR &&
> info->shadow[id].req.u.rw.nr_segments == 0)) {
> - printk(KERN_WARNING "blkfront: %s: empty write %s op failed\n",
> - info->flush_op == BLKIF_OP_WRITE_BARRIER ?
> - "barrier" : "flush disk cache",
> - info->gd->disk_name);
> + printk(KERN_WARNING "blkfront: %s: empty %s op failed\n",
> + info->gd->disk_name, op_name(bret->operation));
> error = -EOPNOTSUPP;
> }
> if (unlikely(error)) {
> --
> 1.7.7.6