[Xen-devel] [PATCH R3 5/7] xen/balloon: Protect against CPU exhaust by event/x proces

[Daniel Kiper <dkiper@xxxxxxxxxxxx>]

Protect against CPU exhaust by event/x process during
errors by adding some delays in scheduling next event.

Signed-off-by: Daniel Kiper <dkiper@xxxxxxxxxxxx>
---
 drivers/xen/balloon.c |   99 +++++++++++++++++++++++++++++++++++++++---------
 1 files changed, 80 insertions(+), 19 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 4223f64..ed103d4 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -66,6 +66,20 @@
 
 #define BALLOON_CLASS_NAME "xen_memory"
 
+/*
+ * balloon_process() state:
+ *
+ * BP_ERROR: error, go to sleep,
+ * BP_DONE: done or nothing to do,
+ * BP_HUNGRY: hungry.
+ */
+
+enum bp_state {
+       BP_ERROR,
+       BP_DONE,
+       BP_HUNGRY
+};
+
 struct balloon_stats {
        /* We aim for 'current allocation' == 'target allocation'. */
        unsigned long current_pages;
@@ -73,6 +87,8 @@ struct balloon_stats {
        /* Number of pages in high- and low-memory balloons. */
        unsigned long balloon_low;
        unsigned long balloon_high;
+       unsigned long schedule_delay;
+       unsigned long max_schedule_delay;
 };
 
 static DEFINE_MUTEX(balloon_mutex);
@@ -171,6 +187,25 @@ static struct page *balloon_next_page(struct page *page)
        return list_entry(next, struct page, lru);
 }
 
+static void update_schedule_delay(enum bp_state state)
+{
+       unsigned long new_schedule_delay;
+
+       if (state != BP_ERROR) {
+               balloon_stats.schedule_delay = 1;
+               return;
+       }
+
+       new_schedule_delay = balloon_stats.schedule_delay << 1;
+
+       if (new_schedule_delay > balloon_stats.max_schedule_delay) {
+               balloon_stats.schedule_delay = balloon_stats.max_schedule_delay;
+               return;
+       }
+
+       balloon_stats.schedule_delay = new_schedule_delay;
+}
+
 static unsigned long current_target(void)
 {
        unsigned long target = balloon_stats.target_pages;
@@ -183,11 +218,12 @@ static unsigned long current_target(void)
        return target;
 }
 
-static int increase_reservation(unsigned long nr_pages)
+static enum bp_state increase_reservation(unsigned long nr_pages)
 {
+       enum bp_state state = BP_DONE;
+       int rc;
        unsigned long  pfn, i;
        struct page   *page;
-       long           rc;
        struct xen_memory_reservation reservation = {
                .address_bits = 0,
                .extent_order = 0,
@@ -198,8 +234,15 @@ static int increase_reservation(unsigned long nr_pages)
                nr_pages = ARRAY_SIZE(frame_list);
 
        page = balloon_first_page();
+
+       if (!page)
+               return BP_ERROR;
+
        for (i = 0; i < nr_pages; i++) {
-               BUG_ON(page == NULL);
+               if (!page) {
+                       nr_pages = i;
+                       break;
+               }
                frame_list[i] = page_to_pfn(page);
                page = balloon_next_page(page);
        }
@@ -207,8 +250,11 @@ static int increase_reservation(unsigned long nr_pages)
        set_xen_guest_handle(reservation.extent_start, frame_list);
        reservation.nr_extents = nr_pages;
        rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
-       if (rc < 0)
-               goto out;
+       if (rc < nr_pages) {
+               if (rc <= 0)
+                       return BP_ERROR;
+               state = BP_HUNGRY;
+       }
 
        for (i = 0; i < rc; i++) {
                page = balloon_retrieve();
@@ -238,15 +284,14 @@ static int increase_reservation(unsigned long nr_pages)
 
        balloon_stats.current_pages += rc;
 
- out:
-       return rc < 0 ? rc : rc != nr_pages;
+       return state;
 }
 
-static int decrease_reservation(unsigned long nr_pages)
+static enum bp_state decrease_reservation(unsigned long nr_pages)
 {
+       enum bp_state state = BP_DONE;
        unsigned long  pfn, i;
        struct page   *page;
-       int            need_sleep = 0;
        int ret;
        struct xen_memory_reservation reservation = {
                .address_bits = 0,
@@ -260,7 +305,7 @@ static int decrease_reservation(unsigned long nr_pages)
        for (i = 0; i < nr_pages; i++) {
                if ((page = alloc_page(GFP_BALLOON)) == NULL) {
                        nr_pages = i;
-                       need_sleep = 1;
+                       state = BP_ERROR;
                        break;
                }
 
@@ -296,7 +341,7 @@ static int decrease_reservation(unsigned long nr_pages)
 
        balloon_stats.current_pages -= nr_pages;
 
-       return need_sleep;
+       return state;
 }
 
 /*
@@ -307,27 +352,35 @@ static int decrease_reservation(unsigned long nr_pages)
  */
 static void balloon_process(struct work_struct *work)
 {
-       int need_sleep = 0;
+       enum bp_state rc, state = BP_DONE;
        long credit;
 
        mutex_lock(&balloon_mutex);
 
        do {
                credit = current_target() - balloon_stats.current_pages;
-               if (credit > 0)
-                       need_sleep = (increase_reservation(credit) != 0);
-               if (credit < 0)
-                       need_sleep = (decrease_reservation(-credit) != 0);
+
+               if (credit > 0) {
+                       rc = increase_reservation(credit);
+                       state = (rc == BP_ERROR) ? BP_ERROR : state;
+               }
+
+               if (credit < 0) {
+                       rc = decrease_reservation(-credit);
+                       state = (rc == BP_ERROR) ? BP_ERROR : state;
+               }
+
+               update_schedule_delay(state);
 
 #ifndef CONFIG_PREEMPT
                if (need_resched())
                        schedule();
 #endif
-       } while ((credit != 0) && !need_sleep);
+       } while (credit && state != BP_ERROR);
 
        /* Schedule more work if there is some still to be done. */
-       if (current_target() != balloon_stats.current_pages)
-               schedule_delayed_work(&balloon_worker, HZ);
+       if (state == BP_ERROR)
+               schedule_delayed_work(&balloon_worker, 
balloon_stats.schedule_delay * HZ);
 
        mutex_unlock(&balloon_mutex);
 }
@@ -394,6 +447,9 @@ static int __init balloon_init(void)
        balloon_stats.balloon_low   = 0;
        balloon_stats.balloon_high  = 0;
 
+       balloon_stats.schedule_delay = 1;
+       balloon_stats.max_schedule_delay = 32;
+
        register_balloon(&balloon_sysdev);
 
        /*
@@ -447,6 +503,9 @@ BALLOON_SHOW(current_kb, "%lu\n", 
PAGES2KB(balloon_stats.current_pages));
 BALLOON_SHOW(low_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_low));
 BALLOON_SHOW(high_kb, "%lu\n", PAGES2KB(balloon_stats.balloon_high));
 
+static SYSDEV_ULONG_ATTR(schedule_delay, 0644, balloon_stats.schedule_delay);
+static SYSDEV_ULONG_ATTR(max_schedule_delay, 0644, 
balloon_stats.max_schedule_delay);
+
 static ssize_t show_target_kb(struct sys_device *dev, struct sysdev_attribute 
*attr,
                              char *buf)
 {
@@ -508,6 +567,8 @@ static SYSDEV_ATTR(target, S_IRUGO | S_IWUSR,
 static struct sysdev_attribute *balloon_attrs[] = {
        &attr_target_kb,
        &attr_target,
+       &attr_schedule_delay.attr,
+       &attr_max_schedule_delay.attr
 };
 
 static struct attribute *balloon_info_attrs[] = {
-- 
1.5.6.5


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