Re: [Bugme-new] [Bug 29302] New: Null pointer dereference with large max_sectors_kb

On 02/21/2011 04:08 PM, Chris Mason wrote:

Excerpts from Tomas Zvala's message of 2011-02-20 06:06:42 -0500:

quoted

On 18.2.2011 21:18, Chris Mason wrote:

quoted

Ok, so it isn't part of the open devices code that prints errors, my
guess is we're failing to read a good super.

Could you please mkfs.btrfs /dev/xxx, sync, then btrfsck /dev/xxx, I want
to make sure things are really getting written.

Here's a patch that makes sure we have a good bdev after scanning,
hopefully it will let us debug things without your box going boom.

-chris

Hello Chris,
I patched the kernel, recompiled and installed, but I don't see the
message in the kernel log.  I forgot to mention before, that
max_hw_sectors_kb and thus max_sectors_kb is 4096.

ok, more below.

quoted

Linux stg-top 2.6.37stg #7 SMP Sun Feb 20 10:48:57 CET 2011 x86_64
Intel(R) Xeon(R) CPU E5620 @ 2.40GHz GenuineIntel GNU/Linux


With default max_sectors_kb = 512
mkfs, sync, btrfsck going through fine
first mount is fine

[112005]stg-top ~ # cat /sys/block/sdb/queue/max_sectors_kb
512
[112012]stg-top ~ # mkfs.btrfs /dev/sdb

WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

fs created label (null) on /dev/sdb
          nodesize 4096 leafsize 4096 sectorsize 4096 size 2.73TB
Btrfs Btrfs v0.19
[112045]stg-top ~ # sync
[112046]stg-top ~ # btrfsck /dev/sdb
found 28672 bytes used err is 0
total csum bytes: 0
total tree bytes: 28672
total fs tree bytes: 8192
btree space waste bytes: 23875
file data blocks allocated: 0
   referenced 0
Btrfs Btrfs v0.19
[112050]stg-top ~ # mount /dev/sdb /mnt/
[112054]stg-top ~ # df /mnt/
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sdb             2929685760        56 2927559936   1% /mnt
[112057]stg-top ~ # umount /mnt


With max_sectors_kb = 4096
mkfs, sync, btrfsck is fine
second mount  BUGs out

[112100]stg-top ~ # echo 4096>  /sys/block/sdb/queue/max_sectors_kb
[112107]stg-top ~ # mkfs.btrfs /dev/sdb

WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

fs created label (null) on /dev/sdb
          nodesize 4096 leafsize 4096 sectorsize 4096 size 2.73TB
Btrfs Btrfs v0.19
[112113]stg-top ~ # sync
[112117]stg-top ~ # btrfsck /dev/sdb
found 28672 bytes used err is 0
total csum bytes: 0
total tree bytes: 28672
total fs tree bytes: 8192
btree space waste bytes: 23875
file data blocks allocated: 0
   referenced 0
Btrfs Btrfs v0.19
[112123]stg-top ~ # mount /dev/sdb /mnt/
Killed

At this point, your box is broken.  You have to reboot before anything
new is valid (sorry).  Could you please:

Set max_sectors_kb to 4096
mkfs.btrfs /dev/xxx
sync
echo 3>  /proc/sys/vm/drop_caches
btrfsck /dev/xxx

Don't try and mount, clearly my patch isn't saving us.

-chris

Hello Chris,
I'm sorry it took so long, I've been a bit busy lately ...

[132926]stg-bot linux-2.6.37-scst # cat 
/sys/block/sdb/queue/max_hw_sectors_kb > /sys/block/sdb/queue/max_sectors_kb
[132932]stg-bot linux-2.6.37-scst # mkfs.btrfs /dev/sdb

WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

fs created label (null) on /dev/sdb
     nodesize 4096 leafsize 4096 sectorsize 4096 size 2.73TB
Btrfs Btrfs v0.19
[132945]stg-bot linux-2.6.37-scst # sync
[132948]stg-bot linux-2.6.37-scst # echo 3 > /proc/sys/vm/drop_caches
[132958]stg-bot linux-2.6.37-scst # btrfsc
btrfsck   btrfsctl
[132958]stg-bot linux-2.6.37-scst # btrfsck /dev/sdb
found 28672 bytes used err is 0
total csum bytes: 0
total tree bytes: 28672
total fs tree bytes: 8192
btree space waste bytes: 23875
file data blocks allocated: 0
  referenced 0
Btrfs Btrfs v0.19


And still cannot mount.


Tomas