Re: [BUG] ext4: cannot unfreeze a filesystem due to a deadlock

[Masayoshi MIZUMA <m.mizuma@jp.fujitsu.com>]

(2011/02/07 20:53), Masayoshi MIZUMA wrote:

> Hi,
> 
> When I checked the freeze feature for ext4 filesystem using fsfreeze command
> at 2.6.38-rc3, I got the following messeges:

Hi,

I checked freeze function with using below test program at 3.2.0-rc4, 
then, I got following messeages and the test program hanged up.
I think this bug is still in  3.2.0-rc4...

The test program:
-----------------------------------------------------------
#!/bin/bash

DEV_1=/dev/sda5
MNT_1=/tmp/sda5
LOOP=500

if [[ ! -d $MNT_1 ]]
then
        mkdir -p $MNT_1
fi

mkfs -t ext4 $DEV_1
mount $DEV_1 $MNT_1

./fsstress -d $MNT_1/tmp -n 10000 -p 100 > /dev/null 2>&1 &
PID=$!

for ((i=0; i<LOOP; i++))
do
        echo LOOP: $i
        fsfreeze -f $MNT_1
        fsfreeze -u $MNT_1
done

kill $PID
-----------------------------------------------------------

The messages I got when I ran the test program is below.
-------------------------------------------------------------
INFO: task flush-8:0:720 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
flush-8:0       D 0000000100521461     0   720      2 0x00000000
 ffff8800b4c41a40 0000000000000046 0000000000000000 0000000000000000
 0000000000013440 ffff8800b4c41fd8 ffff8800b4c40010 0000000000013440
 ffff8800b4c41fd8 0000000000013440 ffffffff81a0d020 ffff8800b464d4e0
Call Trace:
 [<ffffffff81086b4e>] ? prepare_to_wait+0x5e/0x90
 [<ffffffff814ee3ff>] schedule+0x3f/0x60
 [<ffffffffa041e485>] ext4_journal_start_sb+0x145/0x1b0 [ext4]
 [<ffffffff81086820>] ? wake_up_bit+0x40/0x40
 [<ffffffffa0401bc5>] ? ext4_meta_trans_blocks+0xb5/0xc0 [ext4]
 [<ffffffffa0406c9d>] ext4_da_writepages+0x29d/0x620 [ext4]
 [<ffffffff81227a18>] ? blk_finish_plug+0x18/0x50
 [<ffffffff81112bb1>] do_writepages+0x21/0x40
 [<ffffffff8118e380>] writeback_single_inode+0x180/0x3b0
 [<ffffffff8118e971>] writeback_sb_inodes+0x1a1/0x260
 [<ffffffff8118ec6e>] wb_writeback+0xde/0x2b0
 [<ffffffff810739c6>] ? try_to_del_timer_sync+0x86/0xe0
 [<ffffffff8118eee6>] wb_do_writeback+0xa6/0x260
 [<ffffffff81072ef0>] ? lock_timer_base+0x70/0x70
 [<ffffffff8118f14a>] bdi_writeback_thread+0xaa/0x270
 [<ffffffff8118f0a0>] ? wb_do_writeback+0x260/0x260
 [<ffffffff8118f0a0>] ? wb_do_writeback+0x260/0x260
 [<ffffffff810861a6>] kthread+0x96/0xa0
 [<ffffffff814fa5b4>] kernel_thread_helper+0x4/0x10
 [<ffffffff81086110>] ? kthread_worker_fn+0x1a0/0x1a0
 [<ffffffff814fa5b0>] ? gs_change+0x13/0x13

INFO: task fsstress:4376 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
fsstress        D ffff88009b52dda8     0  4376   4364 0x00000080
 ffff88009b52dcb8 0000000000000082 ffffffff810d7e09 ffff88009b52dcc0
 0000000000013440 ffff88009b52dfd8 ffff88009b52c010 0000000000013440
 ffff88009b52dfd8 0000000000013440 ffff88009b4d54e0 ffff8800a1481560
Call Trace:
 [<ffffffff810d7e09>] ? trace_clock_local+0x9/0x10
 [<ffffffff814ee3ff>] schedule+0x3f/0x60
 [<ffffffff814ee89d>] schedule_timeout+0x1fd/0x2e0
 [<ffffffff810e5e43>] ? trace_nowake_buffer_unlock_commit+0x43/0x60
 [<ffffffff810127e4>] ? __switch_to+0x194/0x320
 [<ffffffff8104d623>] ? ftrace_raw_event_sched_switch+0x103/0x110
 [<ffffffff814ee26d>] wait_for_common+0x11d/0x190
 [<ffffffff8105a970>] ? try_to_wake_up+0x2b0/0x2b0
 [<ffffffff814ee3bd>] wait_for_completion+0x1d/0x20
 [<ffffffff8118daef>] writeback_inodes_sb_nr+0x7f/0xa0
 [<ffffffff8118dbdf>] writeback_inodes_sb+0x5f/0x80
 [<ffffffff811938d0>] ? __sync_filesystem+0x90/0x90
 [<ffffffff8119388e>] __sync_filesystem+0x4e/0x90
 [<ffffffff811938ef>] sync_one_sb+0x1f/0x30
 [<ffffffff811695da>] iterate_supers+0x7a/0xd0
 [<ffffffff81193934>] sys_sync+0x34/0x70
 [<ffffffff814f8442>] system_call_fastpath+0x16/0x1b
-------------------------------------------------------------

The test program for xfstests is below.
-------------------------------------------------------------
#! /bin/bash
# FSQA Test No. 277
#
# Run fsstress and  freeze/unfreeze in parallel
#
#-----------------------------------------------------------------------
# Copyright (c) 2006 Silicon Graphics, Inc.  All Rights Reserved.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it would be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write the Free Software Foundation,
# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
#
#-----------------------------------------------------------------------
#
# creator
owner=m.mizuma@jp.fujitsu.com

seq=`basename $0`
echo "QA output created by $seq"

here=`pwd`
tmp=/tmp/$$
status=0        # success is the default!
trap "rm -f $tmp.*; exit \$status" 0 1 2 3 15

# get standard environment, filters and checks
. ./common.rc
. ./common.filter

_workout()
{
	echo ""
	echo "Run fsstress"
	echo ""
	num_iterations=500
	out=$SCRATCH_MNT/fsstress.$$
	args="-p100 -n10000 -d $out"
	echo "fsstress $args" >> $here/$seq.full
	$FSSTRESS_PROG $args > /dev/null 2>&1 &
	pid=$!
	echo "Run xfs_freeze in parallel"
	for ((i=0; i < num_iterations; i++))
	do
		xfs_freeze -f $SCRATCH_MNT | tee -a $seq.full
		xfs_freeze -u $SCRATCH_MNT | tee -a $seq.full
	done
	kill $pid 2> /dev/null
	wait $pid
}

# real QA test starts here
_supported_fs generic
_supported_os Linux
_need_to_be_root
_require_scratch

_scratch_mkfs >> $seq.full 2>&1
_scratch_mount

if ! _workout; then
	umount $SCRATCH_DEV 2>/dev/null
	exit
fi

if ! _scratch_unmount; then
	echo "failed to umount"
	status=1
	exit
fi
_check_scratch_fs
status=$?
exit
-------------------------------------------------------------

Thanks,
Masayoshi Mizuma

> 
> ---------------------------------------------------------------------
> Feb  7 15:05:09 RX300S6 kernel: INFO: task fsfreeze:2104 blocked for more than 120 seconds.
> Feb  7 15:05:09 RX300S6 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> Feb  7 15:05:09 RX300S6 kernel: fsfreeze        D ffff880076d5f040     0  2104   2018 0x00000000
> Feb  7 15:05:09 RX300S6 kernel: ffff88005a9f3d98 0000000000000086 ffff88005a9f3d38 ffffffff00000000
> Feb  7 15:05:09 RX300S6 kernel: 0000000000014d40 ffff880076d5eab0 ffff880076d5f040 ffff88005a9f3fd8
> Feb  7 15:05:09 RX300S6 kernel: ffff880076d5f048 0000000000014d40 ffff88005a9f2010 0000000000014d40
> Feb  7 15:05:09 RX300S6 kernel: Call Trace:
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff814aa5f5>] rwsem_down_failed_common+0xb5/0x140
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff814aa693>] rwsem_down_write_failed+0x13/0x20
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff8122f1a3>] call_rwsem_down_write_failed+0x13/0x20
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff814a9c12>] ? down_write+0x32/0x40
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff81155b48>] thaw_super+0x28/0xd0
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff81164338>] do_vfs_ioctl+0x368/0x560
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff81157c73>] ? sys_newfstat+0x33/0x40
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff811645d1>] sys_ioctl+0xa1/0xb0
> Feb  7 15:05:09 RX300S6 kernel: [<ffffffff8100bf82>] system_call_fastpath+0x16/0x1b
> ...
> Feb  7 15:07:09 RX300S6 kernel: INFO: task flush-8:0:1409 blocked for more than 120 seconds.
> Feb  7 15:07:09 RX300S6 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> Feb  7 15:07:09 RX300S6 kernel: flush-8:0       D ffff880037777a30     0  1409      2 0x00000000
> Feb  7 15:07:09 RX300S6 kernel: ffff880037c95a80 0000000000000046 ffff88007c8037a0 0000000000000000
> Feb  7 15:07:09 RX300S6 kernel: 0000000000014d40 ffff8800377774a0 ffff880037777a30 ffff880037c95fd8
> Feb  7 15:07:09 RX300S6 kernel: ffff880037777a38 0000000000014d40 ffff880037c94010 0000000000014d40
> Feb  7 15:07:09 RX300S6 kernel: Call Trace:
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffffa00abb85>] ext4_journal_start_sb+0x75/0x130 [ext4]
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81082fc0>] ? autoremove_wake_function+0x0/0x40
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffffa0097f0a>] ext4_da_writepages+0x27a/0x640 [ext4]
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81102c91>] do_writepages+0x21/0x40
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff811776b8>] writeback_single_inode+0x98/0x240
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81177cfe>] writeback_sb_inodes+0xce/0x170
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81178709>] writeback_inodes_wb+0x99/0x160
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81178a8b>] wb_writeback+0x2bb/0x430
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81178e2c>] wb_do_writeback+0x22c/0x280
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81178f32>] bdi_writeback_thread+0xb2/0x260
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81178e80>] ? bdi_writeback_thread+0x0/0x260
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81178e80>] ? bdi_writeback_thread+0x0/0x260
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff81082936>] kthread+0x96/0xa0
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff8100cdc4>] kernel_thread_helper+0x4/0x10
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff810828a0>] ? kthread+0x0/0xa0
> Feb  7 15:07:09 RX300S6 kernel: [<ffffffff8100cdc0>] ? kernel_thread_helper+0x0/0x10
> ---------------------------------------------------------------------
> 
> I think the following deadlock problem happened:
> 
>               [flush-8:0:1409]              |          [fsfreeze:2104]
> --------------------------------------------+--------------------------------
> writeback_inodes_wb                         |
>  pin_sb_for_writeback                       |
>    down_read_trylock(&sb->s_umount)         |
>  writeback_sb_inodes                        |thaw_super
>    writeback_single_inode                   | down_write(&sb->s_umount)
>      do_writepages                          |  # stop until flush-8:0 releases
>       ext4_da_writepages                    |  # read lock of sb->s_umount...
>        ext4_journal_start_sb                |
>         vfs_check_frozen                    |
>           wait_event((sb)->s_wait_unfrozen, |
>            ((sb)->s_frozen < (level)))      |
>             # stop until being waked up by  |
>             # fsfreeze...                   |
> --------------------------------------------+--------------------------------
> 
> Could anyone check this problem?
> 
> Thanks,
> Masayoshi Mizuma
> 
> 
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