[PATCH 5.14 030/151] xen/balloon: fix cancelled balloon action

Greg Kroah-Hartman
2021-10-11T14:02:44Z

From: Juergen Gross <jgross@suse.com>

commit 319933a80fd4f07122466a77f93e5019d71be74c upstream.

In case a ballooning action is cancelled the new kernel thread handling
the ballooning might end up in a busy loop.

Fix that by handling the cancelled action gracefully.

While at it introduce a short wait for the BP_WAIT case.

Cc: stable@vger.kernel.org
Fixes: 8480ed9c2bbd56 ("xen/balloon: use a kernel thread instead a workqueue")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20211005133433.32008-1-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/xen/balloon.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)

--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -491,12 +491,12 @@ static enum bp_state decrease_reservatio
}

/*
- * Stop waiting if either state is not BP_EAGAIN and ballooning action is
- * needed, or if the credit has changed while state is BP_EAGAIN.
+ * Stop waiting if either state is BP_DONE and ballooning action is
+ * needed, or if the credit has changed while state is not BP_DONE.
*/
static bool balloon_thread_cond(enum bp_state state, long credit)
{
- if (state != BP_EAGAIN)
+ if (state == BP_DONE)
credit = 0;

return current_credit() != credit || kthread_should_stop();
@@ -516,10 +516,19 @@ static int balloon_thread(void *unused)

set_freezable();
for (;;) {
- if (state == BP_EAGAIN)
- timeout = balloon_stats.schedule_delay * HZ;
- else
+ switch (state) {
+ case BP_DONE:
+ case BP_ECANCELED:
timeout = 3600 * HZ;
+ break;
+ case BP_EAGAIN:
+ timeout = balloon_stats.schedule_delay * HZ;
+ break;
+ case BP_WAIT:
+ timeout = HZ;
+ break;
+ }
+
credit = current_credit();

wait_event_freezable_timeout(balloon_thread_wq,