Date:	Tue, 15 Sep 2015 09:52:18 +0000
From:	Junichi Nomura <j-nomura@...jp.nec.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
CC:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"fengguang.wu@...el.com" <fengguang.wu@...el.com>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	"liwanp@...ux.vnet.ibm.com" <liwanp@...ux.vnet.ibm.com>,
	"david@...morbit.com" <david@...morbit.com>,
	Tejun Heo <tj@...nel.org>,
	"Naoya Horiguchi" <n-horiguchi@...jp.nec.com>
Subject: Test program: check if fsync() can detect I/O error (2/2)

On 09/15/15 17:39, Jun'ichi Nomura wrote:
>> However if admins run a command such as sync or fsfreeze along side,
>> fsync/fdatasync may return success even if writeback has failed.
>> That could lead to data corruption.
>
> For reproducing the problem, compile the attached C program (iogen.c)
> and run with 'runtest.sh' script in the next mail:
>   # gcc -o iogen iogen.c
>   # bash ./runtest.sh

-- cut here --
#!/bin/bash

# preparation for hwpoison injection
export KERNEL_SRC=/lib/modules/$(uname -r)/build
[ -d "$KERNEL_SRC" ] || exit 1 # no kernel source given
make vm -C $KERNEL_SRC/tools || exit 1 # tools/vm failed to build
pagetypes=$KERNEL_SRC/tools/vm/page-types
[ -x $pagetypes ] || exit 1
modprobe hwpoison-inject

# -------------------------------------------------------------------
fstype=ext4

# file name of loopback image
loopfile=test.img
imgsize=16M
lodev=/dev/loop0

# filesystem to use
mkfs=mkfs.$fstype

# device-mapper map name
testmap=testmap

# file name to store device-mapper table data
mapok=testmap.ok
maperr=testmap.err

# mount point and file name used for testing
testdir=/mnt/test
testfile=$testdir/x

# test file size
filesize=16384

# -------------------------------------------------------------------
# Set up
#

endtest() {
	sleep 3
	umount $testdir
	dmsetup remove $testmap
	losetup -d $lodev
	exit
}

# Create loopback device for testing
dd if=/dev/zero of=$loopfile bs=$imgsize count=1
losetup $lodev $loopfile || endtest
if [ ! -b $lodev ]; then
	endtest
fi


# Layer DM device for error injection
echo "0 $(blockdev --getsz $lodev) linear $lodev 0" | dmsetup create $testmap
dmsetup table $testmap > $mapok || endtest
if [ ! -b /dev/mapper/$testmap ]; then
	endtest
fi

# Mount and create target file
mkdir -p $testdir
$mkfs /dev/mapper/$testmap
mount /dev/mapper/$testmap $testdir || endtest
dd if=/dev/zero of=$testfile bs=$filesize count=1 oflag=direct || endtest

# Find physical location of the target file
find_location() {
	# pick up physical block number of file offset 0
	filefrag -v $1 | \
		awk '$1 == "0" {print $3} $1 == "0:" {print $4}' | \
		sed 's/\.//g'
}
filefrag -v $testfile
block=$(find_location $testfile)
if [ -z "$block" ]; then
	endtest
fi
blocksize=$(stat -c %s -f $testfile)
secsize=512
sector=$((block * blocksize / secsize + 1))

# Create error mapping: inject error at $sector
next=$((sector + 1))
total=$(blockdev --getsz $lodev)
remainder=$((total - next))
cat <<EOF > $maperr
0 $sector linear $lodev 0
$sector 1 error
$next $remainder linear $lodev $next
EOF

map_replace() {
	cat $1 | dmsetup load $testmap
	dmsetup suspend --nolockfs $testmap
	dmsetup resume $testmap
}

inject_memory_error() {
	local pfn=0x$($pagetypes -f $testfile -Nl | grep ^1$'\t' | cut -f2)
	[ "$pfn" = 0x ] && return 1 # target pfn not found
	$pagetypes -a $pfn -X -N
}

# -------------------------------------------------------------------
# Test
#

msg() {
	echo $* > /dev/kmsg
	echo $*
}

injector_ioerr_nop() {
	# start
	read x
	msg "TEST: $fstype / ioerr / (no admin action)"

	# inject
	read x
	msg "(admin): Injecting I/O error"
	map_replace $maperr
	msg "(admin): Do nothing"

	# remove
	read x
	map_replace $mapok

	# end
	read x
	umount /dev/mapper/$testmap || endtest
	mount /dev/mapper/$testmap $testdir || endtest
}

injector_ioerr_synccmd() {
	# start
	read x
	msg "TEST: $fstype / ioerr / sync-command"

	# inject
	read x
	msg "(admin): Injecting I/O error"
	map_replace $maperr
	msg "(admin): Calling sync(2)"
	sync

	# remove
	read x
	map_replace $mapok

	# end
	read x
	umount /dev/mapper/$testmap || endtest
	mount /dev/mapper/$testmap $testdir || endtest
}

injector_hwpoison_synccmd() {
	# start
	read x
	msg "TEST: $fstype / memory-error / sync-command"

	# inject
	read x
	msg "(admin): Injecting memory error"
	inject_memory_error
	msg "(admin): Calling sync(2)"
	sync

	# remove
	read x

	# end
	read x
	umount /dev/mapper/$testmap || endtest
	mount /dev/mapper/$testmap $testdir || endtest
}

msg '============'
./iogen $testfile $filesize | injector_ioerr_nop
msg '============'
./iogen $testfile $filesize | injector_ioerr_synccmd
msg '============'
./iogen $testfile $filesize | injector_hwpoison_synccmd

# -------------------------------------------------------------------
# Clean up
#
endtest
--
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