[Xen-devel] [PATCH RFCv2 2/6] mm/memory_hotplug: make add_memory() take the device_hotplug_lock

[David Hildenbrand <david@xxxxxxxxxx>]

add_memory() currently does not take the device_hotplug_lock, however
is aleady called under the lock from
        arch/powerpc/platforms/pseries/hotplug-memory.c
        drivers/acpi/acpi_memhotplug.c
to synchronize against CPU hot-remove and similar.

In general, we should hold the device_hotplug_lock when adding memory
to synchronize against online/offline request (e.g. from user space) -
which already resulted in lock inversions due to device_lock() and
mem_hotplug_lock - see 30467e0b3be ("mm, hotplug: fix concurrent memory
hot-add deadlock"). add_memory()/add_memory_resource() will create memory
block devices, so this really feels like the right thing to do.

Holding the device_hotplug_lock makes sure that a memory block device
can really only be accessed (e.g. via .online/.state) from user space,
once the memory has been fully added to the system.

The lock is not held yet in
        drivers/xen/balloon.c
        arch/powerpc/platforms/powernv/memtrace.c
        drivers/s390/char/sclp_cmd.c
        drivers/hv/hv_balloon.c
So, let's either use the locked variants or take the lock.

Don't export add_memory_resource(), as it once was exported to be used
by XEN, which is never built as a module. If somebody requires it, we
also have to export a locked variant (as device_hotplug_lock is never
exported).

Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Nathan Fontenot <nfont@xxxxxxxxxxxxxxxxxx>
Cc: John Allen <jallen@xxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Mathieu Malaterre <malat@xxxxxxxxxx>
Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: YASUAKI ISHIMATSU <yasu.isimatu@xxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 .../platforms/pseries/hotplug-memory.c        |  2 +-
 drivers/acpi/acpi_memhotplug.c                |  2 +-
 drivers/base/memory.c                         |  9 ++++++--
 drivers/xen/balloon.c                         |  3 +++
 include/linux/memory_hotplug.h                |  1 +
 mm/memory_hotplug.c                           | 22 ++++++++++++++++---
 6 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c 
b/arch/powerpc/platforms/pseries/hotplug-memory.c
index b3f54466e25f..2e6f41dc103a 100644
--- a/arch/powerpc/platforms/pseries/hotplug-memory.c
+++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
@@ -702,7 +702,7 @@ static int dlpar_add_lmb(struct drmem_lmb *lmb)
        nid = memory_add_physaddr_to_nid(lmb->base_addr);
 
        /* Add the memory */
-       rc = add_memory(nid, lmb->base_addr, block_sz);
+       rc = __add_memory(nid, lmb->base_addr, block_sz);
        if (rc) {
                dlpar_remove_device_tree_lmb(lmb);
                return rc;
diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
index 811148415993..8fe0960ea572 100644
--- a/drivers/acpi/acpi_memhotplug.c
+++ b/drivers/acpi/acpi_memhotplug.c
@@ -228,7 +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);
 
-               result = add_memory(node, info->start_addr, info->length);
+               result = __add_memory(node, info->start_addr, info->length);
 
                /*
                 * If the memory block has been used by the kernel, add_memory()
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index c8a1cb0b6136..5b0375be7f65 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -521,15 +521,20 @@ memory_probe_store(struct device *dev, struct 
device_attribute *attr,
        if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
                return -EINVAL;
 
+       ret = lock_device_hotplug_sysfs();
+       if (ret)
+               goto out;
+
        nid = memory_add_physaddr_to_nid(phys_addr);
-       ret = add_memory(nid, phys_addr,
-                        MIN_MEMORY_BLOCK_SIZE * sections_per_block);
+       ret = __add_memory(nid, phys_addr,
+                          MIN_MEMORY_BLOCK_SIZE * sections_per_block);
 
        if (ret)
                goto out;
 
        ret = count;
 out:
+       unlock_device_hotplug();
        return ret;
 }
 
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index e12bb256036f..6bab019a82b1 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -395,7 +395,10 @@ 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, memhp_auto_online);
+       unlock_device_hotplug();
        mutex_lock(&balloon_mutex);
 
        if (rc) {
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 1f096852f479..ffd9cd10fcf3 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -324,6 +324,7 @@ static inline void __remove_memory(int nid, u64 start, u64 
size) {}
 extern void __ref free_area_init_core_hotplug(int nid);
 extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
                void *arg, int (*func)(struct memory_block *, void *));
+extern int __add_memory(int nid, u64 start, u64 size);
 extern int add_memory(int nid, u64 start, u64 size);
 extern int add_memory_resource(int nid, struct resource *resource, bool 
online);
 extern int arch_add_memory(int nid, u64 start, u64 size,
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 898e13d4d87d..e2b5c751e3ea 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1111,7 +1111,12 @@ 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 */
+/*
+ * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
+ * and online/offline operations (triggered e.g. by sysfs).
+ *
+ * we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG
+ */
 int __ref add_memory_resource(int nid, struct resource *res, bool online)
 {
        u64 start, size;
@@ -1180,9 +1185,9 @@ int __ref add_memory_resource(int nid, struct resource 
*res, bool online)
        mem_hotplug_done();
        return ret;
 }
-EXPORT_SYMBOL_GPL(add_memory_resource);
 
-int __ref add_memory(int nid, u64 start, u64 size)
+/* requires device_hotplug_lock, see add_memory_resource() */
+int __ref __add_memory(int nid, u64 start, u64 size)
 {
        struct resource *res;
        int ret;
@@ -1196,6 +1201,17 @@ int __ref add_memory(int nid, u64 start, u64 size)
                release_memory_resource(res);
        return ret;
 }
+
+int add_memory(int nid, u64 start, u64 size)
+{
+       int rc;
+
+       lock_device_hotplug();
+       rc = __add_memory(nid, start, size);
+       unlock_device_hotplug();
+
+       return rc;
+}
 EXPORT_SYMBOL_GPL(add_memory);
 
 #ifdef CONFIG_MEMORY_HOTREMOVE
-- 
2.17.1


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