[PATCH] xen/balloon: fix cancelled balloon action

[Juergen Gross <jgross@xxxxxxxx>]

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@xxxxxxxxxxxxxxx
Fixes: 8480ed9c2bbd56 ("xen/balloon: use a kernel thread instead a workqueue")
Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/balloon.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 43ebfe36ac27..3a50f097ed3e 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -491,12 +491,12 @@ static enum bp_state decrease_reservation(unsigned long 
nr_pages, gfp_t gfp)
 }
 
 /*
- * 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,
-- 
2.26.2