[PATCH RFC 2/2] mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock
David Hildenbrand
david at redhat.com
Fri Aug 17 17:59:01 AEST 2018
There seem to be some problems as result of 30467e0b3be ("mm, hotplug:
fix concurrent memory hot-add deadlock"), which tried to fix a possible
lock inversion reported and discussed in [1] due to the two locks
a) device_lock()
b) mem_hotplug_lock
While add_memory() first takes b), followed by a) during
bus_probe_device(), onlining of memory from user space first took b),
followed by a), exposing a possible deadlock.
In [1], and it was decided to not make use of device_hotplug_lock, but
rather to enforce a locking order. Looking at 1., this order is not always
satisfied when calling device_online() - essentially we simply don't take
one of both locks anymore - and fixing this would require us to
take the mem_hotplug_lock in core driver code (online_store()), which
sounds wrong.
The problems I spotted related to this:
1. Memory block device attributes: While .state first calls
mem_hotplug_begin() and the calls device_online() - which takes
device_lock() - .online does no longer call mem_hotplug_begin(), so
effectively calls online_pages() without mem_hotplug_lock. onlining/
offlining of pages is no longer serialised across different devices.
2. device_online() should be called under device_hotplug_lock, however
onlining memory during add_memory() does not take care of that. (I
didn't follow how strictly this is needed, but there seems to be a
reason because it is documented at device_online() and
device_offline()).
In addition, I think there is also something wrong about the locking in
3. arch/powerpc/platforms/powernv/memtrace.c calls offline_pages()
(and device_online()) without locks. This was introduced after
30467e0b3be. And skimming over the code, I assume it could need some
more care in regards to locking.
ACPI code already holds the device_hotplug_lock, and as we are
effectively hotplugging memory block devices, requiring to hold that
lock does not sound too wrong, although not chosen in [1], as
"I don't think resolving a locking dependency is appropriate by
just serializing them with another lock."
I think this is the cleanest solution.
Requiring add_memory()/add_memory_resource() to be called under
device_hotplug_lock fixes 2., taking the mem_hotplug_lock in
online_pages/offline_pages() fixes 1. and 3.
Fixup all callers of add_memory/add_memory_resource to hold the lock if
not already done.
So this is essentially a revert of 30467e0b3be, implementation of what
was suggested in [1] by Vitaly, applied to the current tree.
[1] http://driverdev.linuxdriverproject.org/pipermail/ driverdev-devel/
2015-February/065324.html
This patch is partly based on a patch by Vitaly Kuznetsov.
Signed-off-by: David Hildenbrand <david at redhat.com>
---
arch/powerpc/platforms/powernv/memtrace.c | 3 ++
drivers/acpi/acpi_memhotplug.c | 1 +
drivers/base/memory.c | 18 +++++-----
drivers/hv/hv_balloon.c | 4 +++
drivers/s390/char/sclp_cmd.c | 3 ++
drivers/xen/balloon.c | 3 ++
mm/memory_hotplug.c | 42 ++++++++++++++++++-----
7 files changed, 55 insertions(+), 19 deletions(-)
diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c
index 51dc398ae3f7..4c2737a33020 100644
--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -206,6 +206,8 @@ static int memtrace_online(void)
int i, ret = 0;
struct memtrace_entry *ent;
+ /* add_memory() requires device_hotplug_lock */
+ lock_device_hotplug();
for (i = memtrace_array_nr - 1; i >= 0; i--) {
ent = &memtrace_array[i];
@@ -244,6 +246,7 @@ static int memtrace_online(void)
pr_info("Added trace memory back to node %d\n", ent->nid);
ent->size = ent->start = ent->nid = -1;
}
+ unlock_device_hotplug();
if (ret)
return ret;
diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
index 6b0d3ef7309c..e7a4c7900967 100644
--- a/drivers/acpi/acpi_memhotplug.c
+++ b/drivers/acpi/acpi_memhotplug.c
@@ -228,6 +228,7 @@ static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
if (node < 0)
node = memory_add_physaddr_to_nid(info->start_addr);
+ /* we already hold the device_hotplug lock at this point */
result = add_memory(node, info->start_addr, info->length);
/*
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index c8a1cb0b6136..f60507f994df 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -341,19 +341,11 @@ 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 protected by device_hotplug_lock */
mem->online_type = online_type;
ret = device_online(&mem->dev);
break;
@@ -364,7 +356,6 @@ store_mem_state(struct device *dev,
ret = -EINVAL; /* should never happen */
}
- mem_hotplug_done();
err:
unlock_device_hotplug();
@@ -522,6 +513,12 @@ memory_probe_store(struct device *dev, struct device_attribute *attr,
return -EINVAL;
nid = memory_add_physaddr_to_nid(phys_addr);
+
+ /* add_memory() requires the device_hotplug_lock */
+ ret = lock_device_hotplug_sysfs();
+ if (ret)
+ return ret;
+
ret = add_memory(nid, phys_addr,
MIN_MEMORY_BLOCK_SIZE * sections_per_block);
@@ -530,6 +527,7 @@ memory_probe_store(struct device *dev, struct device_attribute *attr,
ret = count;
out:
+ unlock_device_hotplug();
return ret;
}
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index b1b788082793..c6d0b654f109 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -735,8 +735,12 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
dm_device.ha_waiting = !memhp_auto_online;
nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
+
+ /* add_memory() requires the device_hotplug lock */
+ lock_device_hotplug();
ret = add_memory(nid, PFN_PHYS((start_pfn)),
(HA_CHUNK << PAGE_SHIFT));
+ unlock_device_hotplug();
if (ret) {
pr_err("hot_add memory failed error is %d\n", ret);
diff --git a/drivers/s390/char/sclp_cmd.c b/drivers/s390/char/sclp_cmd.c
index d7686a68c093..cd0cdab8fcfb 100644
--- a/drivers/s390/char/sclp_cmd.c
+++ b/drivers/s390/char/sclp_cmd.c
@@ -405,8 +405,11 @@ static void __init add_memory_merged(u16 rn)
align_to_block_size(&start, &size, block_size);
if (!size)
goto skip_add;
+ /* add_memory() requires the device_hotplug lock */
+ lock_device_hotplug();
for (addr = start; addr < start + size; addr += block_size)
add_memory(numa_pfn_to_nid(PFN_DOWN(addr)), addr, block_size);
+ unlock_device_hotplug();
skip_add:
first_rn = rn;
num = 1;
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 559e77a20a4d..df1ced4c0692 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -395,8 +395,11 @@ static enum bp_state reserve_additional_memory(void)
* callers drop the mutex before trying again.
*/
mutex_unlock(&balloon_mutex);
+ /* add_memory_resource() requires the device_hotplug lock */
+ lock_device_hotplug();
rc = add_memory_resource(nid, resource->start, resource_size(resource),
memhp_auto_online);
+ unlock_device_hotplug();
mutex_lock(&balloon_mutex);
if (rc) {
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6a2726920ed2..492e558f791b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -885,7 +885,6 @@ static struct zone * __meminit move_pfn_range(int online_type, int nid,
return zone;
}
-/* Must be protected by mem_hotplug_begin() or a device_lock */
int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_type)
{
unsigned long flags;
@@ -897,6 +896,8 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
struct memory_notify arg;
struct memory_block *mem;
+ mem_hotplug_begin();
+
/*
* We can't use pfn_to_nid() because nid might be stored in struct page
* which is not yet initialized. Instead, we find nid from memory block.
@@ -961,6 +962,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
if (onlined_pages)
memory_notify(MEM_ONLINE, &arg);
+ mem_hotplug_done();
return 0;
failed_addition:
@@ -968,6 +970,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
(unsigned long long) pfn << PAGE_SHIFT,
(((unsigned long long) pfn + nr_pages) << PAGE_SHIFT) - 1);
memory_notify(MEM_CANCEL_ONLINE, &arg);
+ mem_hotplug_done();
return ret;
}
#endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
@@ -1115,7 +1118,18 @@ static int online_memory_block(struct memory_block *mem, void *arg)
return device_online(&mem->dev);
}
-/* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
+/*
+ * Requires device_hotplug_lock:
+ *
+ * add_memory_resource() will first take the mem_hotplug_lock and then
+ * device_lock() the created memory block device (via bus_probe_device()).
+ * However, device_online() calls device_lock() and then takes the
+ * mem_hotplug lock (via online_pages()). The device_hotplug_lock makes
+ * sure this lock inversion can never happen - and also device_online()
+ * needs it.
+ *
+ * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
+ */
int __ref add_memory_resource(int nid, u64 start, u64 size, bool online)
{
bool new_node = false;
@@ -1163,25 +1177,26 @@ int __ref add_memory_resource(int nid, u64 start, u64 size, bool online)
/* create new memmap entry */
firmware_map_add_hotplug(start, start + size, "System RAM");
+ /* device_online() will take the lock when calling online_pages() */
+ mem_hotplug_done();
+
/* online pages if requested */
if (online)
walk_memory_range(PFN_DOWN(start), PFN_UP(start + size - 1),
NULL, online_memory_block);
- goto out;
-
+ return ret;
error:
/* rollback pgdat allocation and others */
if (new_node)
rollback_node_hotadd(nid);
memblock_remove(start, size);
-
-out:
mem_hotplug_done();
return ret;
}
EXPORT_SYMBOL_GPL(add_memory_resource);
+/* requires device_hotplug_lock, see add_memory_resource() */
int __ref add_memory(int nid, u64 start, u64 size)
{
struct resource *res;
@@ -1605,10 +1620,16 @@ static int __ref __offline_pages(unsigned long start_pfn,
return -EINVAL;
if (!IS_ALIGNED(end_pfn, pageblock_nr_pages))
return -EINVAL;
+
+ mem_hotplug_begin();
+
/* This makes hotplug much easier...and readable.
we assume this for now. .*/
- if (!test_pages_in_a_zone(start_pfn, end_pfn, &valid_start, &valid_end))
+ if (!test_pages_in_a_zone(start_pfn, end_pfn, &valid_start,
+ &valid_end)) {
+ mem_hotplug_done();
return -EINVAL;
+ }
zone = page_zone(pfn_to_page(valid_start));
node = zone_to_nid(zone);
@@ -1617,8 +1638,10 @@ static int __ref __offline_pages(unsigned long start_pfn,
/* set above range as isolated */
ret = start_isolate_page_range(start_pfn, end_pfn,
MIGRATE_MOVABLE, true);
- if (ret)
+ if (ret) {
+ mem_hotplug_done();
return ret;
+ }
arg.start_pfn = start_pfn;
arg.nr_pages = nr_pages;
@@ -1689,6 +1712,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
writeback_set_ratelimit();
memory_notify(MEM_OFFLINE, &arg);
+ mem_hotplug_done();
return 0;
failed_removal:
@@ -1698,10 +1722,10 @@ 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);
+ mem_hotplug_done();
return ret;
}
-/* Must be protected by mem_hotplug_begin() or a device_lock */
int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
{
return __offline_pages(start_pfn, start_pfn + nr_pages);
--
2.17.1
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