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SubjectRe: [Xen-devel] [PATCH 2/2] xen/blkfront: Add BUG_ON to deal with misbehaving backends.
>>> On 07.06.12 at 23:59, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> wrote:
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -141,14 +141,33 @@ 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 *names[] = {

Could/should really be "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_RESERVED_1] = "reserved",
> + [BLKIF_OP_DISCARD] = "discard" };
> +
> + if (op < 0 || op >= ARRAY_SIZE(names))
> + return "unknown";
> + return names[op];
> +}
> static int xlbd_reserve_minors(unsigned int minor, unsigned int nr)
> {
> unsigned int end = minor + nr;
> @@ -744,20 +763,31 @@ 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)
> + /* We can't safely get the 'struct request' as
> + * the id is busted. So limp along. */
> + goto err_out;

Getting out of the loop here isn't really what I'd call "limp along" -
it'd likely get the communication to a halt (if there are more
responses ready). I'd rather see this print something, and then
continue the loop. Or alternatively, if we really want to stop
communication in such a case, initiate tear down of the device.

> +
> 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))
> + goto err_out;

Same here, obviously.

>
> 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;
> @@ -769,18 +799,14 @@ 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)) {
> @@ -813,12 +839,18 @@ static irqreturn_t blkif_interrupt(int irq, void
> *dev_id)
> goto again;
> } else
> info->ring.sring->rsp_event = i + 1;
> -
> kick_pending_request_queues(info);
>
> spin_unlock_irqrestore(&blkif_io_lock, flags);
>
> return IRQ_HANDLED;
> +err_out:
> + WARN(1, "%s: response to %s has incorrect id\n",
> + info->gd->disk_name, op_name(bret->operation));
> +
> + spin_unlock_irqrestore(&info->io_lock, flags);
> +
> + return IRQ_HANDLED;
> }
>
>
> diff --git a/include/xen/interface/io/blkif.h
> b/include/xen/interface/io/blkif.h
> index ee338bf..bc75c75 100644
> --- a/include/xen/interface/io/blkif.h
> +++ b/include/xen/interface/io/blkif.h
> @@ -59,6 +59,12 @@ typedef uint64_t blkif_sector_t;
> #define BLKIF_OP_FLUSH_DISKCACHE 3
>
> /*
> + * Used in SLES sources for device specific command packet
> + * contained within the request. Reserved for that purpose.
> + */
> +#define BLKIF_OP_RESERVED_1 4

If you really want to give this a numeric tag, wouldn't it be better
to make this _4? But maybe you could leave out the definition here
altogether, and leave the corresponding names[] slot set to NULL?

Jan

> +
> +/*
> * Recognised only if "feature-discard" is present in backend xenbus info.
> * The "feature-discard" node contains a boolean indicating whether trim
> * (ATA) or unmap (SCSI) - conviently called discard requests are likely
> --
> 1.7.7.6




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