[LU-3601] HSM release causes running restore to hang, hangs itself

• Type: Technical task
• Resolution: Fixed
• Priority: Major
• Fix Version/s: Lustre 2.6.0, Lustre 2.5.1
• Affects Version/s: Lustre 2.5.0
• Labels: HSM
• Assignee: Jinshan Xiong (Inactive)
• Reporter: John Hammond

Description

Running the HSM stack as of July 15 2013, I see a hang when a release is issued while a restore is still running. To reproduce I run the following:

#!/bin/bash

export MOUNT_2=n
export MDSCOUNT=1
export PTLDEBUG="super inode ioctl warning dlmtrace error emerg ha rpctrace vfstrace config console"
export DEBUG_SIZE=512

hsm_root=/tmp/hsm_root

rm -rf $hsm_root
mkdir $hsm_root

llmount.sh

lctl conf_param lustre-MDT0000.mdt.hsm_control=enabled
# lctl conf_param lustre-MDT0001.mdt.hsm_control=enabled
sleep 10
lhsmtool_posix --verbose --hsm_root=$hsm_root --bandwidth 1 lustre

lctl dk > ~/hsm-0-mount.dk

set -x
cd /mnt/lustre
lfs setstripe -c2 f0
dd if=/dev/urandom of=f0 bs=1M count=100
lctl dk > ~/hsm-1-dd.dk

lfs hsm_archive f0
sleep 10
echo > /proc/fs/lustre/ldlm/dump_namespaces
lctl dk > ~/hsm-2-archive.dk

lfs hsm_release f0
echo > /proc/fs/lustre/ldlm/dump_namespaces
lctl dk > ~/hsm-3-release.dk

lfs hsm_restore f0
echo > /proc/fs/lustre/ldlm/dump_namespaces
lctl dk > ~/hsm-4-restore.dk

lfs hsm_release f0

with the last command never returning. The MDS_CLOSE handler looks like

10070
[<ffffffffa0f9866e>] cfs_waitq_wait+0xe/0x10 [libcfs]
[<ffffffffa124826a>] ldlm_completion_ast+0x57a/0x960 [ptlrpc]
[<ffffffffa1247920>] ldlm_cli_enqueue_local+0x1f0/0x5c0 [ptlrpc]
[<ffffffffa08cee3b>] mdt_object_lock0+0x33b/0xaf0 [mdt]
[<ffffffffa08cf6b4>] mdt_object_lock+0x14/0x20 [mdt]
[<ffffffffa08f9551>] mdt_mfd_close+0x351/0xde0 [mdt]
[<ffffffffa08fb372>] mdt_close+0x662/0xa60 [mdt]
[<ffffffffa08d2c07>] mdt_handle_common+0x647/0x16d0 [mdt]
[<ffffffffa090c9e5>] mds_readpage_handle+0x15/0x20 [mdt]
[<ffffffffa12813d8>] ptlrpc_server_handle_request+0x398/0xc60 [ptlrpc]
[<ffffffffa128275d>] ptlrpc_main+0xabd/0x1700 [ptlrpc]
[<ffffffff81096936>] kthread+0x96/0xa0
[<ffffffff8100c0ca>] child_rip+0xa/0x20
[<ffffffffffffffff>] 0xffffffffffffffff

while the MDS_HSM_PROGRESS handler looks like:

10065
[<ffffffffa0f9866e>] cfs_waitq_wait+0xe/0x10 [libcfs]
[<ffffffffa124826a>] ldlm_completion_ast+0x57a/0x960 [ptlrpc]
[<ffffffffa1247920>] ldlm_cli_enqueue_local+0x1f0/0x5c0 [ptlrpc]
[<ffffffffa08cee3b>] mdt_object_lock0+0x33b/0xaf0 [mdt]
[<ffffffffa08cf6b4>] mdt_object_lock+0x14/0x20 [mdt]
[<ffffffffa08cf721>] mdt_object_find_lock+0x61/0x170 [mdt]
[<ffffffffa091dc22>] hsm_get_md_attr+0x62/0x270 [mdt]
[<ffffffffa0923253>] mdt_hsm_update_request_state+0x4d3/0x1c20 [mdt]
[<ffffffffa091ae6e>] mdt_hsm_coordinator_update+0x3e/0xe0 [mdt]
[<ffffffffa090931b>] mdt_hsm_progress+0x21b/0x330 [mdt]
[<ffffffffa08d2c07>] mdt_handle_common+0x647/0x16d0 [mdt]
[<ffffffffa090ca05>] mds_regular_handle+0x15/0x20 [mdt]
[<ffffffffa12813d8>] ptlrpc_server_handle_request+0x398/0xc60 [ptlrpc]
[<ffffffffa128275d>] ptlrpc_main+0xabd/0x1700 [ptlrpc]
[<ffffffff81096936>] kthread+0x96/0xa0
[<ffffffff8100c0ca>] child_rip+0xa/0x20
[<ffffffffffffffff>] 0xffffffffffffffff

The close handler is waiting on an EX layout lock on f0. While the
progress handler is waiting on PW update lock on f0. dump_namespaces does not show that the UPDATE lock is granted.

For reference I'm using the following changes:

# LU-2919 hsm: Implementation of exclusive open
# http://review.whamcloud.com/#/c/6730
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/30/6730/13 && git cherry-pick FETCH_HEAD
 
# LU-1333 hsm: Add hsm_release feature.
# http://review.whamcloud.com/#/c/6526
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/26/6526/9 && git cherry-pick FETCH_HEAD
 
# LU-3339 mdt: HSM on disk actions record
# http://review.whamcloud.com/#/c/6529
# MERGED
 
# LU-3340 mdt: HSM memory requests management
# http://review.whamcloud.com/#/c/6530
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/30/6530/8 && git cherry-pick FETCH_HEAD
 
# LU-3341 mdt: HSM coordinator client interface
# http://review.whamcloud.com/#/c/6532
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/32/6532/13 && git cherry-pick FETCH_HEAD
# Needs rebase in sanity-hsm.sh
 
# LU-3342 mdt: HSM coordinator agent interface
# http://review.whamcloud.com/#/c/6534
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/34/6534/8 && git cherry-pick FETCH_HEAD
 
# LU-3343 mdt: HSM coordinator main thread
# http://review.whamcloud.com/#/c/6912
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/12/6912/3 && git cherry-pick FETCH_HEAD
# lustre/mdt/mdt_internal.h
 
# LU-3561 tests: HSM sanity test suite
# http://review.whamcloud.com/#/c/6913/
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/13/6913/4 && git cherry-pick FETCH_HEAD
# lustre/tests/sanity-hsm.sh
 
# LU-3432 llite: Access to released file trigs a restore
# http://review.whamcloud.com/#/c/6537
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/37/6537/11 && git cherry-pick FETCH_HEAD
 
# LU-3363 api: HSM import uses new released pattern
# http://review.whamcloud.com/#/c/6536
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/36/6536/8 && git cherry-pick FETCH_HEAD
 
# LU-2062 utils: HSM Posix CopyTool
# http://review.whamcloud.com/#/c/4737
git fetch http://review.whamcloud.com/fs/lustre-release refs/changes/37/4737/18 && git cherry-pick FETCH_HEAD

Issue Links

• duplicates: LU-4152 layout locks can cause deadlock
• is related to: LU-3608 HSM Master Ticket for 2.5 Landings
• is related to: LU-4152 layout locks can cause deadlock

Comments

[Patrick Farrell (Inactive)]

Jinshan - This was originally a Cray bug (thank you Andriy and Vitaly for bringing this up), which I've been tracking.

I think eliminating the case where 2 locks are taken non-atomically is key long term. If you're planning to do that, then that sounds good.
If you're planning to only do it in certain cases, are you completely sure we don't have another possible live lock?

I'd back Vitaly's suggestion that it be a blocker. We're able to trigger it during testing of NFS export, presumably because of the open_by_fid operations caused by NFS export.

[Jinshan Xiong (Inactive)]

Indeed, this is a live lock case.

To clarify, the process1 must be writing an empty file without layout, so writing will cause new layout to be created.

btw, why the last option was not done originally ?

The reason for me to not acquire one common lock is that we have to acquire EX mode for layout lock which will be too strong for lookup and open lock since they have to share the same DLM lock.

Though patch 7148 can fix this problem, acquiring 2 locks in a row is generally bad. Therefore, I'll fix by acquiring one lock with EX mode for the above case, however, this lock won't be returned to client side. As a result, the process will not cache this specific open. This is good as it will happen rarely.

How do you guys think?

[Vitaly Fertman]

Andreas, it was hit during testing.

process1.lock1: open|lookup, granted
process2.lock1: layout | XXX, granted
process3.lock1: lookup | XXX, waiting process1.lock1
process1.lock2: layout, waiting process2.lock1
process2.lock1: cancelled, reprocessing does not reach process1.lock2

process1 is open by fid
process3 is getattr

in other words, as 2 locks are taken not atomically, you must guarantee nobody can take a conflict for 1st lock in between. otherwise you need either:

• full reprocess
• reordering on waiting list
• make these 2 enqueue atomic
• take 1 common lock with all the ibits

btw, why the last option was not done originally ?

as it can deadlock without HSM, I would consider it as a blocker.

[Andreas Dilger]

Andriy wrote in LU-4152:

LU-1876 adds mdt_object_open_lock() which acquires lock in 2 steps for layout locks.
A deadlock is possible since it isn't atomic and ibits locks are reprocessed until first blocking lock found.

Such situation was hit with mdt_reint_open() & mdt_intent_getattr()

mdt_reint_open()->mdt_open_by_fid_lock() takes first part of the lock (ibits=5),
mdt_intent_getattr() tries to obtain lock (ibits=17)
mdt_open_by_fid_lock() tries to obtain second part but fails due to some conflict with another layout lock2. During cancellation of lock2 only getattr lock is reprocessed.
http://review.whamcloud.com/#/c/7148/1 can help, but it is better to fix mdt_open_by_fid_lock()

Andriy, was this problem actually hit during testing, or was this problem found by code inspection?

[John Hammond]

This issue was fixed for 2.5.0 and can be closed now.

[John Hammond]

Landed after being improved per comments on gerrit.

[Jodi Levi (Inactive)]

Should Change, 7148 be landed or abandoned?

[jacques-charles lafoucriere]

sanity-hsm #33 hits the same bug, but was not designed to test concurrent access to file during the restore phase. We also today do no test rename/rm during restore.

[Aurelien Degremont (Inactive)]

We already have such test. sanity-hsm #33 deadlock was hitting this bug. John's patch was fixing hit. I will confirm that the latest coordinator, without John's patch do not trig this deadlock anymore on monday, but I'm confident.

[jacques-charles lafoucriere]

We will add sanity-hsm tests for the 2 simple use cases. Will be safer for futures changes.

[John Hammond]

Since the removal of UPDATE lock use from the coordinator, I can no longer reproduce these issues.