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xenbus: Make xenbus_switch_state transactional

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According to the comments, this was how it's been done years ago, but
apparently took an xbt pointer from elsewhere back then. The code was
removed because of consistency issues: cancellation wont't roll back
the saved xbdev->state.

Still, unsolicited writes to the state field remain an issue,
especially if device shutdown takes thread synchronization, and subtle
races cause accidental recreation of the device node.

Fixed by reintroducing the transaction. An internal one is sufficient,
so the xbdev->state value remains consistent.

Also fixes the original hack to prevent infinite recursion. Instead of
bailing out on the first attempt to switch to Closing, checks call
depth now.

Signed-off-by: Daniel Stodden <daniel.stodden@citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
This commit is contained in:
Daniel Stodden 2010-04-30 22:01:15 +00:00 committed by Jens Axboe
parent 2def141e71
commit 5b61cb90c2
1 changed files with 77 additions and 35 deletions
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112
drivers/xen/xenbus/xenbus_client.c
View file

@ -133,6 +133,64 @@ int xenbus_watch_pathfmt(struct xenbus_device *dev,
}
EXPORT_SYMBOL_GPL(xenbus_watch_pathfmt);
static void xenbus_switch_fatal(struct xenbus_device *, int, int,
const char *, ...);
static int
__xenbus_switch_state(struct xenbus_device *dev,
enum xenbus_state state, int depth)
{
/* We check whether the state is currently set to the given value, and
if not, then the state is set. We don't want to unconditionally
write the given state, because we don't want to fire watches
unnecessarily. Furthermore, if the node has gone, we don't write
to it, as the device will be tearing down, and we don't want to
resurrect that directory.
Note that, because of this cached value of our state, this
function will not take a caller's Xenstore transaction
(something it was trying to in the past) because dev->state
would not get reset if the transaction was aborted.
*/
struct xenbus_transaction xbt;
int current_state;
int err, abort;
if (state == dev->state)
return 0;
again:
abort = 1;
err = xenbus_transaction_start(&xbt);
if (err) {
xenbus_switch_fatal(dev, depth, err, "starting transaction");
return 0;
}
err = xenbus_scanf(xbt, dev->nodename, "state", "%d", &current_state);
if (err != 1)
goto abort;
err = xenbus_printf(xbt, dev->nodename, "state", "%d", state);
if (err) {
xenbus_switch_fatal(dev, depth, err, "writing new state");
goto abort;
}
abort = 0;
abort:
err = xenbus_transaction_end(xbt, abort);
if (err) {
if (err == -EAGAIN && !abort)
goto again;
xenbus_switch_fatal(dev, depth, err, "ending transaction");
} else
dev->state = state;
return 0;
}
/**
* xenbus_switch_state
@ -145,42 +203,9 @@ EXPORT_SYMBOL_GPL(xenbus_watch_pathfmt);
*/
int xenbus_switch_state(struct xenbus_device *dev, enum xenbus_state state)
{
/* We check whether the state is currently set to the given value, and
if not, then the state is set. We don't want to unconditionally
write the given state, because we don't want to fire watches
unnecessarily. Furthermore, if the node has gone, we don't write
to it, as the device will be tearing down, and we don't want to
resurrect that directory.
Note that, because of this cached value of our state, this function
will not work inside a Xenstore transaction (something it was
trying to in the past) because dev->state would not get reset if
the transaction was aborted.
*/
int current_state;
int err;
if (state == dev->state)
return 0;
err = xenbus_scanf(XBT_NIL, dev->nodename, "state", "%d",
&current_state);
if (err != 1)
return 0;
err = xenbus_printf(XBT_NIL, dev->nodename, "state", "%d", state);
if (err) {
if (state != XenbusStateClosing) /* Avoid looping */
xenbus_dev_fatal(dev, err, "writing new state");
return err;
}
dev->state = state;
return 0;
return __xenbus_switch_state(dev, state, 0);
}
EXPORT_SYMBOL_GPL(xenbus_switch_state);
int xenbus_frontend_closed(struct xenbus_device *dev)
@ -283,6 +308,23 @@ void xenbus_dev_fatal(struct xenbus_device *dev, int err, const char *fmt, ...)
}
EXPORT_SYMBOL_GPL(xenbus_dev_fatal);
/**
* Equivalent to xenbus_dev_fatal(dev, err, fmt, args), but helps
* avoiding recursion within xenbus_switch_state.
*/
static void xenbus_switch_fatal(struct xenbus_device *dev, int depth, int err,
const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
xenbus_va_dev_error(dev, err, fmt, ap);
va_end(ap);
if (!depth)
__xenbus_switch_state(dev, XenbusStateClosing, 1);
}
/**
* xenbus_grant_ring
* @dev: xenbus device