mm, hotplug: fix concurrent memory hot-add deadlock

There's a deadlock when concurrently hot-adding memory through the probe
interface and switching a memory block from offline to online.

When hot-adding memory via the probe interface, add_memory() first takes
mem_hotplug_begin() and then device_lock() is later taken when registering
the newly initialized memory block.  This creates a lock dependency of (1)
mem_hotplug.lock (2) dev->mutex.

When switching a memory block from offline to online, dev->mutex is first
grabbed in device_online() when the write(2) transitions an existing
memory block from offline to online, and then online_pages() will take
mem_hotplug_begin().

This creates a lock inversion between mem_hotplug.lock and dev->mutex.
Vitaly reports that this deadlock can happen when kworker handling a probe
event races with systemd-udevd switching a memory block's state.

This patch requires the state transition to take mem_hotplug_begin()
before dev->mutex.  Hot-adding memory via the probe interface creates a
memory block while holding mem_hotplug_begin(), there is no way to take
dev->mutex first in this case.

online_pages() and offline_pages() are only called when transitioning
memory block state.  We now require that mem_hotplug_begin() is taken
before calling them -- this requires exporting the mem_hotplug_begin() and
mem_hotplug_done() to generic code.  In all hot-add and hot-remove cases,
mem_hotplug_begin() is done prior to device_online().  This is all that is
needed to avoid the deadlock.

Signed-off-by: David Rientjes <rientjes@google.com>
Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Tested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zhang Zhen <zhenzhang.zhang@huawei.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: Wang Nan <wangnan0@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index ab5c9a7..2804aed 100644 (file)
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -219,6 +219,7 @@ static bool pages_correctly_reserved(unsigned long start_pfn)
 /*
  * MEMORY_HOTPLUG depends on SPARSEMEM in mm/Kconfig, so it is
  * OK to have direct references to sparsemem variables in here.
+ * Must already be protected by mem_hotplug_begin().
  */
 static int
 memory_block_action(unsigned long phys_index, unsigned long action, int online_type)
@@ -286,6 +287,7 @@ static int memory_subsys_online(struct device *dev)
        if (mem->online_type < 0)
                mem->online_type = MMOP_ONLINE_KEEP;
 
+       /* Already under protection of mem_hotplug_begin() */
        ret = memory_block_change_state(mem, MEM_ONLINE, MEM_OFFLINE);
 
        /* clear online_type */
@@ -328,17 +330,19 @@ store_mem_state(struct device *dev,
                goto err;
        }
 
+       /*
+        * Memory hotplug needs to hold mem_hotplug_begin() for probe to find
+        * the correct memory block to online before doing device_online(dev),
+        * which will take dev->mutex.  Take the lock early to prevent an
+        * inversion, memory_subsys_online() callbacks will be implemented by
+        * assuming it's already protected.
+        */
+       mem_hotplug_begin();
+
        switch (online_type) {
        case MMOP_ONLINE_KERNEL:
        case MMOP_ONLINE_MOVABLE:
        case MMOP_ONLINE_KEEP:
-               /*
-                * mem->online_type is not protected so there can be a
-                * race here.  However, when racing online, the first
-                * will succeed and the second will just return as the
-                * block will already be online.  The online type
-                * could be either one, but that is expected.
-                */
                mem->online_type = online_type;
                ret = device_online(&mem->dev);
                break;
@@ -349,6 +353,7 @@ store_mem_state(struct device *dev,
                ret = -EINVAL; /* should never happen */
        }
 
+       mem_hotplug_done();
 err:
        unlock_device_hotplug();
 

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 8f1a419..6ffa0ac 100644 (file)
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -192,6 +192,9 @@ extern void get_page_bootmem(unsigned long ingo, struct page *page,
 void get_online_mems(void);
 void put_online_mems(void);
 
+void mem_hotplug_begin(void);
+void mem_hotplug_done(void);
+
 #else /* ! CONFIG_MEMORY_HOTPLUG */
 /*
  * Stub functions for when hotplug is off
@@ -231,6 +234,9 @@ static inline int try_online_node(int nid)
 static inline void get_online_mems(void) {}
 static inline void put_online_mems(void) {}
 
+static inline void mem_hotplug_begin(void) {}
+static inline void mem_hotplug_done(void) {}
+
 #endif /* ! CONFIG_MEMORY_HOTPLUG */
 
 #ifdef CONFIG_MEMORY_HOTREMOVE

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index aaec775..e2e8014 100644 (file)
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -104,7 +104,7 @@ void put_online_mems(void)
 
 }
 
-static void mem_hotplug_begin(void)
+void mem_hotplug_begin(void)
 {
        mem_hotplug.active_writer = current;
 
@@ -119,7 +119,7 @@ static void mem_hotplug_begin(void)
        }
 }
 
-static void mem_hotplug_done(void)
+void mem_hotplug_done(void)
 {
        mem_hotplug.active_writer = NULL;
        mutex_unlock(&mem_hotplug.lock);
@@ -959,6 +959,7 @@ static void node_states_set_node(int node, struct memory_notify *arg)
 }
 
 
+/* Must be protected by mem_hotplug_begin() */
 int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_type)
 {
        unsigned long flags;
@@ -969,7 +970,6 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
        int ret;
        struct memory_notify arg;
 
-       mem_hotplug_begin();
        /*
         * This doesn't need a lock to do pfn_to_page().
         * The section can't be removed here because of the
@@ -977,21 +977,20 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
         */
        zone = page_zone(pfn_to_page(pfn));
 
-       ret = -EINVAL;
        if ((zone_idx(zone) > ZONE_NORMAL ||
            online_type == MMOP_ONLINE_MOVABLE) &&
            !can_online_high_movable(zone))
-               goto out;
+               return -EINVAL;
 
        if (online_type == MMOP_ONLINE_KERNEL &&
            zone_idx(zone) == ZONE_MOVABLE) {
                if (move_pfn_range_left(zone - 1, zone, pfn, pfn + nr_pages))
-                       goto out;
+                       return -EINVAL;
        }
        if (online_type == MMOP_ONLINE_MOVABLE &&
            zone_idx(zone) == ZONE_MOVABLE - 1) {
                if (move_pfn_range_right(zone, zone + 1, pfn, pfn + nr_pages))
-                       goto out;
+                       return -EINVAL;
        }
 
        /* Previous code may changed the zone of the pfn range */
@@ -1007,7 +1006,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
        ret = notifier_to_errno(ret);
        if (ret) {
                memory_notify(MEM_CANCEL_ONLINE, &arg);
-               goto out;
+               return ret;
        }
        /*
         * If this zone is not populated, then it is not in zonelist.
@@ -1031,7 +1030,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
                       (((unsigned long long) pfn + nr_pages)
                            << PAGE_SHIFT) - 1);
                memory_notify(MEM_CANCEL_ONLINE, &arg);
-               goto out;
+               return ret;
        }
 
        zone->present_pages += onlined_pages;
@@ -1061,9 +1060,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
 
        if (onlined_pages)
                memory_notify(MEM_ONLINE, &arg);
-out:
-       mem_hotplug_done();
-       return ret;
+       return 0;
 }
 #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
 
@@ -1688,21 +1685,18 @@ static int __ref __offline_pages(unsigned long start_pfn,
        if (!test_pages_in_a_zone(start_pfn, end_pfn))
                return -EINVAL;
 
-       mem_hotplug_begin();
-
        zone = page_zone(pfn_to_page(start_pfn));
        node = zone_to_nid(zone);
        nr_pages = end_pfn - start_pfn;
 
-       ret = -EINVAL;
        if (zone_idx(zone) <= ZONE_NORMAL && !can_offline_normal(zone, nr_pages))
-               goto out;
+               return -EINVAL;
 
        /* set above range as isolated */
        ret = start_isolate_page_range(start_pfn, end_pfn,
                                       MIGRATE_MOVABLE, true);
        if (ret)
-               goto out;
+               return ret;
 
        arg.start_pfn = start_pfn;
        arg.nr_pages = nr_pages;
@@ -1795,7 +1789,6 @@ repeat:
        writeback_set_ratelimit();
 
        memory_notify(MEM_OFFLINE, &arg);
-       mem_hotplug_done();
        return 0;
 
 failed_removal:
@@ -1805,12 +1798,10 @@ failed_removal:
        memory_notify(MEM_CANCEL_OFFLINE, &arg);
        /* pushback to free area */
        undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
-
-out:
-       mem_hotplug_done();
        return ret;
 }
 
+/* Must be protected by mem_hotplug_begin() */
 int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 {
        return __offline_pages(start_pfn, start_pfn + nr_pages, 120 * HZ);