[v3] memory-hotplug: Fix kernel warning during memory hotplug on ppc64

This patch fixes a bug where a kernel warning is triggered when performing
a memory hotplug on ppc64. This warning may also occur on any architecture
that uses the memory_probe_store interface.

WARNING: at drivers/base/memory.c:200
CPU: 9 PID: 13042 Comm: systemd-udevd Not tainted 4.4.0-rc4-00113-g0bd0f1e-dirty #7
NIP [c00000000055e034] pages_correctly_reserved+0x134/0x1b0
LR [c00000000055e7f8] memory_subsys_online+0x68/0x140
Call Trace:
[c0000000fa9e7b50] [c0000000fa9e7b90] 0xc0000000fa9e7b90 (unreliable)
[c0000000fa9e7bb0] [c00000000055e7f8] memory_subsys_online+0x68/0x140
[c0000000fa9e7bf0] [c000000000540064] device_online+0xb4/0x120
[c0000000fa9e7c30] [c00000000055e6c0] store_mem_state+0xb0/0x180
[c0000000fa9e7c70] [c00000000053c5e4] dev_attr_store+0x34/0x60
[c0000000fa9e7c90] [c0000000002db0a4] sysfs_kf_write+0x64/0xa0
[c0000000fa9e7cb0] [c0000000002da0cc] kernfs_fop_write+0x17c/0x1e0
[c0000000fa9e7d00] [c0000000002481b0] __vfs_write+0x40/0x160
[c0000000fa9e7d90] [c000000000248ce8] vfs_write+0xb8/0x200
[c0000000fa9e7de0] [c000000000249b40] SyS_write+0x60/0x110
[c0000000fa9e7e30] [c000000000009260] system_call+0x38/0xd0

The warning is triggered because there is a udev rule that automatically
tries to online memory after it has been added. The udev rule varies from
distro to distro, but will generally look something like:

SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline", ATTR{state}="online"

On any architecture that uses memory_probe_store to reserve memory, the
udev rule will be triggered after the first section of the block is
reserved and will subsequently attempt to online the entire block,
interrupting the memory reservation process and causing the warning.
This patch modifies memory_probe_store to add a block of memory with
a single call to add_memory as opposed to looping through and adding
each section individually. A single call to add_memory is protected by
the mem_hotplug mutex which will prevent the udev rule from onlining
memory until the reservation of the entire block is complete.

Signed-off-by: John Allen <jallen@linux.vnet.ibm.com>
---
v2: -Move call to unlock_device_hotplug under "out" label
v3: -Update changelog with trimmed traces from newer kernel
    -After further testing and reviewing the original purpose of
     the lock_device_hotplug_sysfs mutex, modified solution to
     fix the issue by replacing loop that adds memory section
     by section with a single call to add_memory.

Hi John,

[auto build test WARNING on v4.4-rc8]
[also build test WARNING on next-20160106]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/John-Allen/memory-hotplug-Fix-kernel-warning-during-memory-hotplug-on-ppc64/20160107-053749
config: x86_64-randconfig-x017-01041832 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   drivers/base/memory.c: In function 'memory_probe_store':
>> drivers/base/memory.c:454:6: warning: unused variable 'i' [-Wunused-variable]
     int i, ret;
         ^

vim +/i +454 drivers/base/memory.c

3947be19 Dave Hansen     2005-10-29  438  
10fbcf4c Kay Sievers     2011-12-21  439  static DEVICE_ATTR(block_size_bytes, 0444, print_block_size, NULL);
3947be19 Dave Hansen     2005-10-29  440  
3947be19 Dave Hansen     2005-10-29  441  /*
3947be19 Dave Hansen     2005-10-29  442   * Some architectures will have custom drivers to do this, and
3947be19 Dave Hansen     2005-10-29  443   * will not need to do it from userspace.  The fake hot-add code
3947be19 Dave Hansen     2005-10-29  444   * as well as ppc64 will do all of their discovery in userspace
3947be19 Dave Hansen     2005-10-29  445   * and will require this interface.
3947be19 Dave Hansen     2005-10-29  446   */
3947be19 Dave Hansen     2005-10-29  447  #ifdef CONFIG_ARCH_MEMORY_PROBE
3947be19 Dave Hansen     2005-10-29  448  static ssize_t
10fbcf4c Kay Sievers     2011-12-21  449  memory_probe_store(struct device *dev, struct device_attribute *attr,
28812fe1 Andi Kleen      2010-01-05  450  		   const char *buf, size_t count)
3947be19 Dave Hansen     2005-10-29  451  {
3947be19 Dave Hansen     2005-10-29  452  	u64 phys_addr;
bc02af93 Yasunori Goto   2006-06-27  453  	int nid;
6add7cd6 Nathan Fontenot 2011-01-31 @454  	int i, ret;
61b94fea Anton Blanchard 2011-09-15  455  	unsigned long pages_per_block = PAGES_PER_SECTION * sections_per_block;
3947be19 Dave Hansen     2005-10-29  456  
b69deb2b Zhang Zhen      2014-08-06  457  	ret = kstrtoull(buf, 0, &phys_addr);
b69deb2b Zhang Zhen      2014-08-06  458  	if (ret)
b69deb2b Zhang Zhen      2014-08-06  459  		return ret;
3947be19 Dave Hansen     2005-10-29  460  
61b94fea Anton Blanchard 2011-09-15  461  	if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
61b94fea Anton Blanchard 2011-09-15  462  		return -EINVAL;

:::::: The code at line 454 was first introduced by commit
:::::: 6add7cd618b4d4dc525731beb539c5e06e891855 memory hotplug: sysfs probe routine should add all memory sections

:::::: TO: Nathan Fontenot <nfont@austin.ibm.com>
:::::: CC: Greg Kroah-Hartman <gregkh@suse.de>

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