[Bug 118041] My tricky script involving zram and device mapper hangs on "mount"

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https://bugzilla.kernel.org/show_bug.cgi?id=118041

--- Comment #4 from Navin <navinp1912@gmail.com> ---
Not related to ext4 . I can reproduce this with below script and i think 
dm-devel@redhat.com should be contacted.


I tested on Linux junk-foo 4.2.0-35-generic from Ubuntu (15.10 ) x64.
Linux junk-foo 4.2.0-35-generic #40-Ubuntu SMP Tue Mar 15 22:15:45 UTC 2016
x86_64 x86_64 x86_64 GNU/Linux



Here is a script that crashes the kernel for me with out of memory. Looks to be
a dm problem because it occurs with dd,mkfs.xfs,mkfs.vat ,without zram ie with
losetup.

Here is the script.Should be run as root for losetup and dmsetup permissions.


#!/bin/bash

fallocate -l 50M 50M_file_unused
fallocate -l 60M 60M_file_unused
losetup  /dev/loop4 50M_file_unused
losetup  /dev/loop5 60M_file_unused

MS=$(blockdev --getsize /dev/loop4)
WS=$(blockdev --getsize /dev/loop5)
echo "0 $MS linear /dev/loop4 0 \n $MS $WS linear /dev/loop5 0" | dmsetup
create cryptie4-ff
DS=$(blockdev --getsize /dev/mapper/cryptie4-ff)
MN=$(printf '%d:%d' `stat -Lc '0x%t 0x%T' /dev/loop4`)
WN=$(printf '%d:%d' `stat -Lc '0x%t 0x%T' /dev/loop5`)
DN=$(printf '%d:%d' `stat -Lc '0x%t 0x%T'  /dev/mapper/cryptie4-ff`)

#pv /dev/mapper/cryptie4-ff | hashed_update /dev/stdin NULL /dev/zram0
/tmp/ff.md5 65536
pv /dev/mapper/cryptie4-ff 
dmsetup create ff --table "0 $MS snapshot-origin $MN"


After this  doing this 
dd if=/dev/zero of=/dev/mapper/ff
or
mkfs.xfs /mkfs.ext4 on /dev/mapper/ff will fail.

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