From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mikulas Patocka <mpatocka@redhat.com>
Subject: Re: write directly to device mapper snapshot origin
	device ?
Date: Fri, 15 Jul 2016 09:50:25 -0400 (EDT)
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To: "Navin P.S" <navinp1912@gmail.com>
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> Are origin devices readonly ?
> 
> When i do dd if=/dev/zero of=/dev/mapper/ff count=10, it kills all the
> process says OOM.
> 
> How do you go about debugging this ? I'm running 4.7.0-rc7+ .

Find some older kernel where this worked.

Use the git bisect tool on the kernel tree to find out which patch broke 
it.

Mikulas

> root@vm-xenial-foo:~# dmsetup info
> Name:              cryptie4-ff
> State:             ACTIVE
> Read Ahead:        256
> Tables present:    LIVE
> Open count:        0
> Event number:      0
> Major, minor:      251, 0
> Number of targets: 2
> 
> Name:              ff
> State:             ACTIVE
> Read Ahead:        256
> Tables present:    LIVE
> Open count:        0
> Event number:      0
> Major, minor:      251, 1
> Number of targets: 1
> 
> root@vm-xenial-foo:~# dmsetup status
> cryptie4-ff: 0 102400 linear
> cryptie4-ff: 102400 122880 linear
> ff: 0 102400 snapshot-origin
> root@vm-xenial-foo:~#
> 
> 
> 
> 
> free -m
>               total        used        free      shared  buff/cache   available
> Mem:           7762        2178        3720         358        1864        4920
> Swap:         19145           0       19145
> 
> 
> -- 
> -- Navin
>