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block: set device_list.tqe_prev to NULL on BDS removal

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This fixes a regression introduced with commit 3f09bfbc7.  Multiple
bugs arise in conjunction with live snapshots and mirroring operations
(which include active layer commit).

After a live snapshot occurs, the active layer and the base layer both
have a non-NULL tqe_prev field in the device_list, although the base
node's tqe_prev field points to a NULL entry.  This non-NULL tqe_prev
field occurs after the bdrv_append() in the external snapshot calls
change_parent_backing_link().

In change_parent_backing_link(), when the previous active layer is
removed from device_list, the device_list.tqe_prev pointer is not
set to NULL.

The operating scheme in the block layer is to indicate that a BDS belongs
in the bdrv_states device_list iff the device_list.tqe_prev pointer
is non-NULL.

This patch does two things:

1.) Introduces a new block layer helper bdrv_device_remove() to remove a
    BDS from the device_list, and
2.) uses that new API, which also fixes the regression once used in
    change_parent_backing_link().

Signed-off-by: Jeff Cody <jcody@redhat.com>
Message-id: 0cd51e11c0666c04ddb7c05293fe94afeb551e89.1454376655.git.jcody@redhat.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Jeff Cody 2016-02-01 20:33:10 -05:00 • committed by Max Reitz
parent c7fc50d376
commit f8aa905a4f
3 changed files with 16 additions and 12 deletions
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24
block.c
View file

@ -2242,21 +2242,25 @@ void bdrv_close_all(void)
}
}
/* Note that bs->device_list.tqe_prev is initially null,
* and gets set to non-null by QTAILQ_INSERT_TAIL(). Establish
* the useful invariant "bs in bdrv_states iff bs->tqe_prev" by
* resetting it to null on remove. */
void bdrv_device_remove(BlockDriverState *bs)
{
QTAILQ_REMOVE(&bdrv_states, bs, device_list);
bs->device_list.tqe_prev = NULL;
}
/* make a BlockDriverState anonymous by removing from bdrv_state and
* graph_bdrv_state list.
Also, NULL terminate the device_name to prevent double remove */
void bdrv_make_anon(BlockDriverState *bs)
{
/*
* Take care to remove bs from bdrv_states only when it's actually
* in it. Note that bs->device_list.tqe_prev is initially null,
* and gets set to non-null by QTAILQ_INSERT_TAIL(). Establish
* the useful invariant "bs in bdrv_states iff bs->tqe_prev" by
* resetting it to null on remove.
*/
/* Take care to remove bs from bdrv_states only when it's actually
* in it. */
if (bs->device_list.tqe_prev) {
QTAILQ_REMOVE(&bdrv_states, bs, device_list);
bs->device_list.tqe_prev = NULL;
bdrv_device_remove(bs);
}
if (bs->node_name[0] != '\0') {
QTAILQ_REMOVE(&graph_bdrv_states, bs, node_list);
@ -2297,7 +2301,7 @@ static void change_parent_backing_link(BlockDriverState *from,
if (!to->device_list.tqe_prev) {
QTAILQ_INSERT_BEFORE(from, to, device_list);
}
QTAILQ_REMOVE(&bdrv_states, from, device_list);
bdrv_device_remove(from);
}
}