xen_balloon: support memory auto onlining policy

Add support for the newly added kernel memory auto onlining policy to
Xen ballon driver.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Suggested-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Daniel Kiper <daniel.kiper@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Kay Sievers <kay@vrfy.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 25 insertions, 9 deletions

diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index 73708acce3ca..979a8317204f 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -37,23 +37,30 @@ config XEN_BALLOON_MEMORY_HOTPLUG
 
           Memory could be hotplugged in following steps:
 
-            1) dom0: xl mem-max <domU> <maxmem>
+            1) target domain: ensure that memory auto online policy is in
+               effect by checking /sys/devices/system/memory/auto_online_blocks
+               file (should be 'online').
+
+            2) control domain: xl mem-max <target-domain> <maxmem>
                where <maxmem> is >= requested memory size,
 
-            2) dom0: xl mem-set <domU> <memory>
+            3) control domain: xl mem-set <target-domain> <memory>
                where <memory> is requested memory size; alternatively memory
                could be added by writing proper value to
                /sys/devices/system/xen_memory/xen_memory0/target or
-               /sys/devices/system/xen_memory/xen_memory0/target_kb on dumU,
+               /sys/devices/system/xen_memory/xen_memory0/target_kb on the
+               target domain.
 
-            3) domU: for i in /sys/devices/system/memory/memory*/state; do \
-                       [ "`cat "$i"`" = offline ] && echo online > "$i"; done
+          Alternatively, if memory auto onlining was not requested at step 1
+          the newly added memory can be manually onlined in the target domain
+          by doing the following:
 
-          Memory could be onlined automatically on domU by adding following line to udev rules:
+                for i in /sys/devices/system/memory/memory*/state; do \
+                  [ "`cat "$i"`" = offline ] && echo online > "$i"; done
 
-          SUBSYSTEM=="memory", ACTION=="add", RUN+="/bin/sh -c '[ -f /sys$devpath/state ] && echo online > /sys$devpath/state'"
+          or by adding the following line to udev rules:
 
-          In that case step 3 should be omitted.
+          SUBSYSTEM=="memory", ACTION=="add", RUN+="/bin/sh -c '[ -f /sys$devpath/state ] && echo online > /sys$devpath/state'"
 
 config XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
         int "Hotplugged memory limit (in GiB) for a PV guest"
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index e6058debd01b..7c8a2cf16f58 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -338,7 +338,16 @@ static enum bp_state reserve_additional_memory(void)
         }
 #endif
 
-        rc = add_memory_resource(nid, resource, false);
+        /*
+         * add_memory_resource() will call online_pages() which in its turn
+         * will call xen_online_page() callback causing deadlock if we don't
+         * release balloon_mutex here. Unlocking here is safe because the
+         * callers drop the mutex before trying again.
+         */
+        mutex_unlock(&balloon_mutex);
+        rc = add_memory_resource(nid, resource, memhp_auto_online);
+        mutex_lock(&balloon_mutex);
+
         if (rc) {
                 pr_warn("Cannot add additional memory (%i)\n", rc);
                 goto err;