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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/2] xen/blkfront: Add BUG_ON to deal with misbehaving backends.
On Thu, 7 Jun 2012, Konrad Rzeszutek Wilk wrote:
> On Fri, Jun 01, 2012 at 11:16:29AM +0100, Stefano Stabellini wrote:
> > On Thu, 31 May 2012, Konrad Rzeszutek Wilk wrote:
> > > The blkfront_remove part is .. that is going to take some surgery to do
> > > and I don't think I am going to be able to attempt that within the next
> > > couple
> > > of weeks. So lets put that on the TODO list and just do this one?
> >
> > OK
> >
> > > >From 4aabb5b44778fc0c0b8d4f5a2e2cd8e8490064d7 Mon Sep 17 00:00:00 2001
> > > From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > 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]
> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > > ---
> > > drivers/block/xen-blkfront.c | 39
> > > +++++++++++++++++++++++++++++----------
> > > 1 files changed, 29 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> > > index 60eed4b..c7ef8a4 100644
> > > --- a/drivers/block/xen-blkfront.c
> > > +++ b/drivers/block/xen-blkfront.c
> > > @@ -144,11 +144,22 @@ static int get_id_from_freelist(struct
> > > blkfront_info *info)
> > > static void add_id_to_freelist(struct blkfront_info *info,
> > > unsigned long id)
> > > {
> > > + BUG_ON(info->shadow[id].req.u.rw.id != id);
> > > info->shadow[id].req.u.rw.id = info->shadow_free;
> > > + BUG_ON(info->shadow[id].request == NULL);
> > > info->shadow[id].request = NULL;
> > > info->shadow_free = id;
> > > }
> >
> > Like Jan said, it would be best to change the two BUG_ON into WARN_ON
> > and return an error.
>
> Yes. I missed that.
> >
> >
> > > +static const char *op_name(int op)
> > > +{
> > > + const char *names[BLKIF_OP_DISCARD+1] = {
> > > + "read" , "write", "barrier", "flush", "reserved", "discard"};
> > > +
> > > + if (op > BLKIF_OP_DISCARD)
> > > + return "unknown";
> > > + return names[op];
> > > +}
> >
> > Considering that op is an int, shoudn't we check for negative values
> > too?
>
> Yes! I also converted this per Jan's excellent idea.
>
> Please see:
>
>
> >From 3877611c3096423a7741e99e9c9b9e63a9f2e557 Mon Sep 17 00:00:00 2001
> From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> 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]
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> drivers/block/xen-blkfront.c | 58 +++++++++++++++++++++++++++++--------
> include/xen/interface/io/blkif.h | 6 ++++
> 2 files changed, 51 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 2f22874..ae8e3b7 100644
> --- 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[] = {
> + [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;
> +
> 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;
>
> 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
> +
> +/*
> * 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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