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xen-block: Fix removal of backend instance via xenstore

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Whenever a Xen block device is detach via xenstore, the image
associated with it remained open by the backend QEMU and an error is
logged:
    qemu-system-i386: failed to destroy drive: Node xvdz-qcow2 is in use

This happened since object_unparent() doesn't immediately frees the
object and thus keep a reference to the node we are trying to free.
The reference is hold by the "drive" property and the call
xen_block_drive_destroy() fails.

In order to fix that, we call drain_call_rcu() to run the callback
setup by bus_remove_child() via object_unparent().

Fixes: 2d24a6466154 ("device-core: use RCU for list of children of a bus")

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Message-Id: <20210308143232.83388-1-anthony.perard@citrix.com>
This commit is contained in:
Anthony PERARD 2021-03-08 14:32:32 +00:00
parent 5ca634afcf
commit b807ca3fa0
1 changed files with 9 additions and 0 deletions
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9
hw/block/xen-block.c
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@ -972,6 +972,15 @@ static void xen_block_device_destroy(XenBackendInstance *backend,
object_unparent(OBJECT(xendev));
/*
* Drain all pending RCU callbacks as object_unparent() frees `xendev'
* in a RCU callback.
* And due to the property "drive" still existing in `xendev', we
* can't destroy the XenBlockDrive associated with `xendev' with
* xen_block_drive_destroy() below.
*/
drain_call_rcu();
if (iothread) {
xen_block_iothread_destroy(iothread, errp);
if (*errp) {