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xen/blkfront: Fix crash if backend doesn't follow the right states.

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We have split the setting up of all the resources in two steps:
1) talk_to_blkback  - which figures out the num_ring_pages (from
   the default value of zero), sets up shadow and so
2) blkfront_connect - does the real part of filling out the
   internal structures.

The problem is if we bypass the 1) step and go straight to 2)
and call blkfront_setup_indirect where we use the macro
BLK_RING_SIZE - which returns an negative value (because
sz is zero  - since num_ring_pages is zero - since it has never
been set).

We can fix this by making sure that we always have called
talk_to_blkback before going to blkfront_connect.

Or we could set in blkfront_probe info->nr_ring_pages = 1
to have a default value. But that looks odd - as we haven't
actually negotiated any ring size.

This patch changes XenbusStateConnected state to detect if
we haven't done the initial handshake - and if so continue
on as if were in XenbusStateInitWait state.

We also roll the error recovery (freeing the structure) into
talk_to_blkback error path - which is safe since that function
is only called from blkback_changed.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Konrad Rzeszutek Wilk 2015-12-18 16:28:53 -05:00
parent 93bb277f97
commit c31ecf6c12
1 changed files with 8 additions and 4 deletions
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12
drivers/block/xen-blkfront.c
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@ -1867,6 +1867,9 @@ again:
destroy_blkring:
blkif_free(info, 0);
kfree(info);
dev_set_drvdata(&dev->dev, NULL);
return err;
}
@ -2453,11 +2456,8 @@ static void blkback_changed(struct xenbus_device *dev,
case XenbusStateInitWait:
if (dev->state != XenbusStateInitialising)
break;
if (talk_to_blkback(dev, info)) {
kfree(info);
dev_set_drvdata(&dev->dev, NULL);
if (talk_to_blkback(dev, info))
break;
}
case XenbusStateInitialising:
case XenbusStateInitialised:
case XenbusStateReconfiguring:
@ -2466,6 +2466,10 @@ static void blkback_changed(struct xenbus_device *dev,
break;
case XenbusStateConnected:
if (dev->state != XenbusStateInitialised) {
if (talk_to_blkback(dev, info))
break;
}
blkfront_connect(info);
break;