device-dax: fix memory and resource leak if hotplug fails

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
memory.

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.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: c221c0b0308f ("device-dax: "Hotplug" persistent memory for use like normal RAM")
Signed-off-by: Pavel Tatashin <[email protected]>
Reviewed-by: Dave Hansen <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Fengguang Wu <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: James Morris <[email protected]>
Cc: Jérôme Glisse <[email protected]>
Cc: Keith Busch <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Ross Zwisler <[email protected]>
Cc: Sasha Levin <[email protected]>
Cc: Takashi Iwai <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Vishal Verma <[email protected]>
Cc: Yaowei Bai <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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