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Re: (ITS#7715) SIGBUS when mdb is configured with writemap

On Fri, Oct 4, 2013 at 10:26 AM, <hyc@symas.com> wrote:
> Thanks. So far the output shows nothing out of the ordinary. Can you also
> provide the output for:
>     ls -l /opt/openldap/var/openldap-data

root@spr101:~ $ ls -ahl /opt/openldap/var/openldap-data
total 100K
drwxr-xr-x. 2 openldap openldap 4.0K Oct  4 07:54 .
drwxr-xr-x. 4 openldap openldap 4.0K May 28 08:49 ..
-rw-------. 1 openldap openldap  88K Oct  4 07:44 data.mdb
-rw-------. 1 openldap openldap 8.0K Oct  4 07:54 lock.mdb

root@spr101:~ $ ps -efa | grep slapd
openldap 44012     1  0 07:54 ?        00:00:01
/opt/openldap/libexec/slapd -h ldap:/// ldapi:/// -F
/opt/openldap/etc/openldap/slapd.d -g openldap -u openldap

root@spr101:~ $ mount | grep sdb1
/dev/sdb1 on /opt type ext4 (rw,noatime,nobarrier,data=ordered)
Do note that we did load testing on ext2 and ext4, with both being
tweaked and not, and as far as I recall, every combination of
parameters causes the problem; I will try to reproduce it on
ext{2,3,4} with default mounting parameters. Almost forgot, we did
tests using tmpfs also, with the same outcome. The whole /opt was used
as a mount point for the tmpfs.

root@spr101:~ $ fdisk -lu /dev/sdb1
Disk /dev/sdb1: 400.0 GB, 400027127808 bytes
224 heads, 56 sectors/track, 62284 cylinders, total 781302984 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

gparted doesn't seem to be complaining about SSD block alignment:
root@spr101:~ $ parted /dev/sdb1 align-check opt 1

Another thing I'll be trying is making a partition with different
alignment parameters to see if any change occurs; tried using a
different scheme, but that hasn't produced a a change in behavior.

> Note from the mmap(2) manpage:
>         Use of a mapped region can result in these signals:
>         SIGSEGV
>                Attempted write into a region mapped as read-only.
>         SIGBUS Attempted access to a portion of the buffer that does not
> correspond to the file (for  example,  beyond
>                the end of the file, including the case where another process
> has truncated the file).
> LMDB always sets the size of the file when using the WRITEMAP option, so the
> SIGBUS condition should never happen. The pointers in your gdb output are all
> within the bounds of the map and mapsize you configured.
> What filesystem type is the data directory stored on? This is looking more
> like a kernel or filesystem bug than anything else.
> --
>    -- Howard Chu
>    CTO, Symas Corp.           http://www.symas.com
>    Director, Highland Sun     http://highlandsun.com/hyc/
>    Chief Architect, OpenLDAP  http://www.openldap.org/project/