[patch 067/166] hv_balloon: don't check for memhp_auto_online manually

Andrew Morton
2020-04-07T03:07:36Z

From: David Hildenbrand <david@redhat.com>
Subject: hv_balloon: don't check for memhp_auto_online manually

We get the MEM_ONLINE notifier call if memory is added right from the
kernel via add_memory() or later from user space.

Let's get rid of the "ha_waiting" flag - the wait event has an inbuilt
mechanism (->done) for that. Initialize the wait event only once and
reinitialize before adding memory. Unconditionally call complete() and
wait_for_completion_timeout().

If there are no waiters, complete() will only increment ->done - which
will be reset by reinit_completion(). If complete() has already been
called, wait_for_completion_timeout() will not wait.

There is still the chance for a small race between concurrent
reinit_completion() and complete(). If complete() wins, we would not wait
- which is tolerable (and the race exists in current code as well).

Note: We only wait for "some" memory to get onlined, which seems to be
good enough for now.

[akpm@linux-foundation.org: register_memory_notifier() after init_completion(), per David]
Link: http://lkml.kernel.org/r/20200317104942.11178-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Yumei Huang <yuhuang@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

drivers/hv/hv_balloon.c | 25 ++++++++++---------------
1 file changed, 10 insertions(+), 15 deletions(-)

--- a/drivers/hv/hv_balloon.c~hv_balloon-dont-check-for-memhp_auto_online-manually
+++ a/drivers/hv/hv_balloon.c
@@ -533,7 +533,6 @@ struct hv_dynmem_device {
* State to synchronize hot-add.
*/
struct completion ol_waitevent;
- bool ha_waiting;
/*
* This thread handles hot-add
* requests from the host as well as notifying
@@ -634,10 +633,7 @@ static int hv_memory_notifier(struct not
switch (val) {
case MEM_ONLINE:
case MEM_CANCEL_ONLINE:
- if (dm_device.ha_waiting) {
- dm_device.ha_waiting = false;
- complete(&dm_device.ol_waitevent);
- }
+ complete(&dm_device.ol_waitevent);
break;

case MEM_OFFLINE:
@@ -726,8 +722,7 @@ static void hv_mem_hot_add(unsigned long
has->covered_end_pfn += processed_pfn;
spin_unlock_irqrestore(&dm_device.ha_lock, flags);

- init_completion(&dm_device.ol_waitevent);
- dm_device.ha_waiting = !memhp_auto_online;
+ reinit_completion(&dm_device.ol_waitevent);

nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
ret = add_memory(nid, PFN_PHYS((start_pfn)),
@@ -753,15 +748,14 @@ static void hv_mem_hot_add(unsigned long
}

/*
- * Wait for the memory block to be onlined when memory onlining
- * is done outside of kernel (memhp_auto_online). Since the hot
- * add has succeeded, it is ok to proceed even if the pages in
- * the hot added region have not been "onlined" within the
- * allowed time.
+ * Wait for memory to get onlined. If the kernel onlined the
+ * memory when adding it, this will return directly. Otherwise,
+ * it will wait for user space to online the memory. This helps
+ * to avoid adding memory faster than it is getting onlined. As
+ * adding succeeded, it is ok to proceed even if the memory was
+ * not onlined in time.
*/
- if (dm_device.ha_waiting)
- wait_for_completion_timeout(&dm_device.ol_waitevent,
- 5*HZ);
+ wait_for_completion_timeout(&dm_device.ol_waitevent, 5 * HZ);
post_status(&dm_device);
}
}
@@ -1706,6 +1700,7 @@ static int balloon_probe(struct hv_devic

#ifdef CONFIG_MEMORY_HOTPLUG
set_online_page_callback(&hv_online_page);
+ init_completion(&dm_device.ol_waitevent);
register_memory_notifier(&hv_memory_nb);
#endif

_