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Bug 1275230

Summary: memory unplug triggers BUG_ON: kernel BUG at mm/memory_hotplug.c:703!
Product: Red Hat Enterprise Linux 7 Reporter: Igor Mammedov <imammedo>
Component: qemu-kvm-rhevAssignee: Igor Mammedov <imammedo>
Status: CLOSED ERRATA QA Contact: Virtualization Bugs <virt-bugs>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 7.2CC: chayang, hhuang, huding, jkurik, juzhang, knoel, lmiksik, ovasik, sherold, tlavigne, virt-maint, xfu, yuhuang
Target Milestone: rcKeywords: ZStream
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: qemu-kvm-rhev-2.5.0-1.el7 Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
: 1278282 (view as bug list) Environment:
Last Closed: 2016-11-07 20:48:40 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1278282, 1288337, 1305606    

Description Igor Mammedov 2015-10-26 10:16:48 UTC 
Description of problem:
commit aa8580cd "pc: memhp: force gaps between DIMM's GPA"
regressed memory hot-unplug for linux guests triggering
following BUGON
 =====
 kernel BUG at mm/memory_hotplug.c:703!
 ...
 [<ffffffff81385fa7>] acpi_memory_device_remove+0x79/0xa5
 [<ffffffff81357818>] acpi_bus_trim+0x5a/0x8d
 [<ffffffff81359026>] acpi_device_hotplug+0x1b7/0x418
 ===
    BUG_ON(phys_start_pfn & ~PAGE_SECTION_MASK);
 ===

reson for it is that x86-64 linux guest supports memory
hotplug in chunks of 128Mb and memory section also should
be 128Mb aligned.
However gaps forced between 128Mb DIMMs with backend's
natural alignment of 2Mb make the 2nd and following
DIMMs not being aligned on 128Mb boundary as it was
originally.


Version-Release number of selected component (if applicable):
qemu-kvm-rhev-2.3.0-31

How reproducible:
100%

Steps to Reproduce:
1. start RHEL72 guest liek this:
 /usr/libexec/qemu-kvm -enable-kvm  -m 4G,slots=8,maxmem=32G rhel72.img  -object memory-backend-ram,id=m0,size=1G -device pc-dimm,id=dimm0,memdev=m0  -snapshot -numa node -object memory-backend-ram,id=m1,size=1G -device pc-dimm,id=dimm1,memdev=m1 -monitor unix:/tmp/u,server,nowait -nographic

2. execute following command twice:
 echo "device_del dimm1" | nc -U /tmp/u

Actual results:
guest crash

Expected results:
no guest crash
Comment 7 Yumei Huang 2016-05-19 02:58:31 UTC 
Reproduce:
qemu-kvm-rhev-2.3.0-31.el7
kernel-3.10.0-366.el7.x86_64

Steps:
1. boot rhel7.2 guest:
# /usr/libexec/qemu-kvm -name rhel72-sn5 -m 4G,slots=8,maxmem=40G  \

-smp 4,sockets=4,cores=1,threads=1 -no-user-config -nodefaults -rtc base=utc,driftfix=slew -global kvm-pit.lost_tick_policy=discard \

-boot menu=on,strict=on -object iothread,id=iothread0 -drive file=/home/guest/RHEL-Server-7.2-64-virtio.qcow2,if=none,id=drive-data-disk,format=qcow2,cache=none,aio=native,werror=stop,rerror=stop  -device virtio-blk-pci,drive=drive-data-disk,id=data-disk,iothread=iothread0,bus=pci.0,addr=0x7   \

-netdev tap,id=hostnet1,vhost=on -device e1000,netdev=hostnet1,id=net2,mac=10:1a:4a:42:0a:0b,bus=pci.0,addr=0xa -usb -device usb-tablet,id=input0 -vga qxl   \

-spice port=5901,addr=0.0.0.0,disable-ticketing,image-compression=off,seamless-migration=on -monitor unix:/tmp/monitor3,server,nowait -serial unix:/tmp/console,server,nowait -monitor stdio


2. Hotplug memory 5 times via script 
#!/bin/bash 
i=0 
while [ $i -lt 5 ] 
do 
echo $i 
sleep 3 
echo "object_add memory-backend-ram,id=mem$i,size=128M"|nc -U /tmp/monitor3 
sleep 2 
echo "device_add pc-dimm,id=dimm$i,memdev=mem$i,slot=$i"|nc -U /tmp/monitor3 
i=$(($i+1)) 
done 

3. Unplug memory 5 times via script; 
#!/bin/bash
i=0
while [ $i -lt 5 ]
do
echo $i
sleep 3
echo "device_del dimm$i"|nc -U /tmp/monitor3
echo "object_del mem$i"|nc -U /tmp/monitor3
sleep 2
i=$(($i+1))
done 

After step 3, guest crashed. Got "kernel BUG at mm/memory_hotplug.c:703!" in the guest console. 
So the bug is reproduced. 

Verify:
qemu-kvm-rhev-2.6.0-1.el7
kernel-3.10.0-366.el7.x86_64

With same steps as above, guest works well.
So the bug is fixed.
Comment 10 errata-xmlrpc 2016-11-07 20:48:40 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2016-2673.html