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During a suspend/resume, the xenwatch thread waits for all outstanding
xenstore requests and transactions to complete. This does not work
correctly for transactions started by userspace because it waits for
them to complete after freezing userspace threads which means the
transactions have no way of completing, resulting in a deadlock. This is
trivial to reproduce by running this script and then suspending the VM:
import pyxs, time
c = pyxs.client.Client(xen_bus_path="/dev/xen/xenbus")
c.connect()
c.transaction()
time.sleep(3600)
Even if this deadlock were resolved, misbehaving userspace should not
prevent a VM from being migrated. So, instead of waiting for these
transactions to complete before suspending, store the current generation
id for each transaction when it is started. The global generation id is
incremented during resume. If the caller commits the transaction and the
generation id does not match the current generation id, return EAGAIN so
that they try again. If the transaction was instead discarded, return OK
since no changes were made anyway.
This only affects users of the xenbus file interface. In-kernel users of
xenbus are assumed to be well-behaved and complete all transactions
before freezing.
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
139 lines
4.2 KiB
C
139 lines
4.2 KiB
C
/*
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* Private include for xenbus communications.
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*
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* Copyright (C) 2005 Rusty Russell, IBM Corporation
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* Copyright (C) 2005 XenSource Ltd.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License version 2
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* as published by the Free Software Foundation; or, when distributed
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* separately from the Linux kernel or incorporated into other
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* software packages, subject to the following license:
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this source file (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use, copy, modify,
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* merge, publish, distribute, sublicense, and/or sell copies of the Software,
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* and to permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*/
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#ifndef _XENBUS_XENBUS_H
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#define _XENBUS_XENBUS_H
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#include <linux/mutex.h>
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#include <linux/uio.h>
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#include <xen/xenbus.h>
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#define XEN_BUS_ID_SIZE 20
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struct xen_bus_type {
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char *root;
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unsigned int levels;
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int (*get_bus_id)(char bus_id[XEN_BUS_ID_SIZE], const char *nodename);
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int (*probe)(struct xen_bus_type *bus, const char *type,
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const char *dir);
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void (*otherend_changed)(struct xenbus_watch *watch, const char *path,
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const char *token);
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struct bus_type bus;
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};
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enum xenstore_init {
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XS_UNKNOWN,
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XS_PV,
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XS_HVM,
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XS_LOCAL,
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};
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struct xs_watch_event {
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struct list_head list;
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unsigned int len;
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struct xenbus_watch *handle;
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const char *path;
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const char *token;
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char body[];
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};
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enum xb_req_state {
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xb_req_state_queued,
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xb_req_state_wait_reply,
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xb_req_state_got_reply,
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xb_req_state_aborted
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};
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struct xb_req_data {
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struct list_head list;
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wait_queue_head_t wq;
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struct xsd_sockmsg msg;
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uint32_t caller_req_id;
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enum xsd_sockmsg_type type;
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char *body;
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const struct kvec *vec;
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int num_vecs;
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int err;
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enum xb_req_state state;
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bool user_req;
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void (*cb)(struct xb_req_data *);
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void *par;
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};
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extern enum xenstore_init xen_store_domain_type;
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extern const struct attribute_group *xenbus_dev_groups[];
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extern struct mutex xs_response_mutex;
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extern struct list_head xs_reply_list;
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extern struct list_head xb_write_list;
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extern wait_queue_head_t xb_waitq;
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extern struct mutex xb_write_mutex;
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int xs_init(void);
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int xb_init_comms(void);
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void xb_deinit_comms(void);
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int xs_watch_msg(struct xs_watch_event *event);
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void xs_request_exit(struct xb_req_data *req);
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int xenbus_match(struct device *_dev, struct device_driver *_drv);
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int xenbus_dev_probe(struct device *_dev);
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int xenbus_dev_remove(struct device *_dev);
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int xenbus_register_driver_common(struct xenbus_driver *drv,
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struct xen_bus_type *bus,
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struct module *owner,
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const char *mod_name);
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int xenbus_probe_node(struct xen_bus_type *bus,
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const char *type,
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const char *nodename);
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int xenbus_probe_devices(struct xen_bus_type *bus);
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void xenbus_dev_changed(const char *node, struct xen_bus_type *bus);
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void xenbus_dev_shutdown(struct device *_dev);
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int xenbus_dev_suspend(struct device *dev);
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int xenbus_dev_resume(struct device *dev);
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int xenbus_dev_cancel(struct device *dev);
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void xenbus_otherend_changed(struct xenbus_watch *watch,
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const char *path, const char *token,
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int ignore_on_shutdown);
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int xenbus_read_otherend_details(struct xenbus_device *xendev,
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char *id_node, char *path_node);
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void xenbus_ring_ops_init(void);
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int xenbus_dev_request_and_reply(struct xsd_sockmsg *msg, void *par);
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void xenbus_dev_queue_reply(struct xb_req_data *req);
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extern unsigned int xb_dev_generation_id;
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#endif
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