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mm, hotplug: fix concurrent memory hot-add deadlock

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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>
This commit is contained in:
David Rientjes 2015-04-14 15:45:11 -07:00 committed by Linus Torvalds
parent 17e0db822b
commit 30467e0b3b
3 changed files with 30 additions and 28 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

19
drivers/base/memory.c
View file

@ -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();

6
include/linux/memory_hotplug.h
View file

@ -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

33
mm/memory_hotplug.c
View file

@ -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 @@ static int __ref __offline_pages(unsigned long start_pfn,
writeback_set_ratelimit();
memory_notify(MEM_OFFLINE, &arg);
mem_hotplug_done();
return 0;
failed_removal:
@ -1805,12 +1798,10 @@ static int __ref __offline_pages(unsigned long start_pfn,
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);