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Subject[PATCH AUTOSEL 5.2 67/85] device-dax: fix memory and resource leak if hotplug fails
From: Pavel Tatashin <>

[ Upstream commit 31e4ca92a7dd4cdebd7fe1456b3b0b6ace9a816f ]

Patch series ""Hotremove" persistent memory", v6.

Recently, adding a persistent memory to be used like a regular RAM was
added to Linux. This work extends this functionality to also allow hot
removing persistent memory.

We (Microsoft) have an important use case for this functionality.

The requirement is for physical machines with small amount of RAM (~8G)
to be able to reboot in a very short period of time (<1s). Yet, there
is a userland state that is expensive to recreate (~2G).

The solution is to boot machines with 2G preserved for persistent

Copy the state, and hotadd the persistent memory so machine still has
all 8G available for runtime. Before reboot, offline and hotremove
device-dax 2G, copy the memory that is needed to be preserved to pmem0
device, and reboot.

The series of operations look like this:

1. After boot restore /dev/pmem0 to ramdisk to be consumed by apps.
and free ramdisk.
2. Convert raw pmem0 to devdax
ndctl create-namespace --mode devdax --map mem -e namespace0.0 -f
3. Hotadd to System RAM
echo dax0.0 > /sys/bus/dax/drivers/device_dax/unbind
echo dax0.0 > /sys/bus/dax/drivers/kmem/new_id
echo online_movable > /sys/devices/system/memoryXXX/state
4. Before reboot hotremove device-dax memory from System RAM
echo offline > /sys/devices/system/memoryXXX/state
echo dax0.0 > /sys/bus/dax/drivers/kmem/unbind
5. Create raw pmem0 device
ndctl create-namespace --mode raw -e namespace0.0 -f
6. Copy the state that was stored by apps to ramdisk to pmem device
7. Do kexec reboot or reboot through firmware if firmware does not
zero memory in pmem0 region (These machines have only regular
volatile memory). So to have pmem0 device either memmap kernel
parameter is used, or devices nodes in dtb are specified.

This patch (of 3):

When add_memory() fails, the resource and the memory should be freed.

Fixes: c221c0b0308f ("device-dax: "Hotplug" persistent memory for use like normal RAM")
Signed-off-by: Pavel Tatashin <>
Reviewed-by: Dave Hansen <>
Cc: Bjorn Helgaas <>
Cc: Borislav Petkov <>
Cc: Dan Williams <>
Cc: Dave Hansen <>
Cc: Dave Jiang <>
Cc: David Hildenbrand <>
Cc: Fengguang Wu <>
Cc: Huang Ying <>
Cc: James Morris <>
Cc: Jérôme Glisse <>
Cc: Keith Busch <>
Cc: Michal Hocko <>
Cc: Ross Zwisler <>
Cc: Sasha Levin <>
Cc: Takashi Iwai <>
Cc: Tom Lendacky <>
Cc: Vishal Verma <>
Cc: Yaowei Bai <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Sasha Levin <>
drivers/dax/kmem.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index a02318c6d28a..4c0131857133 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -66,8 +66,11 @@ int dev_dax_kmem_probe(struct device *dev)
new_res->name = dev_name(dev);

rc = add_memory(numa_node, new_res->start, resource_size(new_res));
- if (rc)
+ if (rc) {
+ release_resource(new_res);
+ kfree(new_res);
return rc;
+ }

return 0;
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