Re: [PATCH] Btrfs: fix fsync deadlock in log_new_dir_dentries

Tue, 11 Oct 2016 00:48:44 -0700 

Hi Filipe:

why did you replace the continue statement with a break statement:
because we released ahead of the path, it can not continue to use,
need to jump out, and then go to again.

supplement:
We found a fsync deadlock ie. 32021->32020->32028->14431->14436->32021, the number id pid. 
extent_buffer: start:207060992, len:16384
    locker pid: 32020 read lock
    wait pid: 32021 write lock
extent_buffer: start:14730821632, len:16384
    locker pid: 32028 read lock
    wait pid: 32020 write lock
extent_buffer: start:446503813120, len:16384
    locker pid: 14431 write lock
    wait pid: 32028 read lock
extent_buffer: start:446503845888, len: 16384
    locker pid: 14436 write lock
    wait pid: 14431 write lock
extent_buffer: start: 446504386560, len: 16384
    locker pid: 32021 write lock
    wait pid: 14436 write lock

Thanks.
Robbie Ko

Filipe Manana 於 2016-10-07 18:46 寫到:
On Fri, Oct 7, 2016 at 11:43 AM, robbieko <robbi...@synology.com> wrote: 
Hi Filipe,

I am sorry, I express not clear enough.
This number is pid, and the above are their call trace respectively.


And why did you replace the continue statement with a break statement?

Also please avoid mixing inline replies with top posting, it just
breaks the thread.

thanks



Thanks.
robbieko

Filipe Manana <fdman...@gmail.com> 於 2016-10-07 18:23 寫道：
On Fri, Oct 7, 2016 at 11:05 AM, robbieko <robbi...@synology.com> wrote: 
From: Robbie Ko <robbi...@synology.com>
We found a fsync deadlock ie. 32021->32020->32028->14431->14436->32021, in log_new_dir_dentries, because btrfs_search_forward get path lock, then call btrfs_iget will get another extent_buffer lock, maybe occur deadlock. 

What are those numbers? Are they inode numbers?
If so you're suggesting a deadlock due to recursive logging of the same 
inode.
However the trace below, and the code change, has nothing to do with that. 
It's just about btrfs_iget trying to do a search on a btree and
attempting to read lock some node/leaf that already has a write lock
acquired previously by the same task.

Please be more clear on your change logs.




we can release path before call btrfs_iget, avoid deadlock occur.

some process call trace like below:
[ 4077.478852] kworker/u24:10  D ffff88107fc90640     0 14431      2
0x00000000
[ 4077.486752] Workqueue: btrfs-endio-write btrfs_endio_write_helper
[btrfs]
[ 4077.494346]  ffff880ffa56bad0 0000000000000046 0000000000009000
ffff880ffa56bfd8
[ 4077.502629]  ffff880ffa56bfd8 ffff881016ce21c0 ffffffffa06ecb26
ffff88101a5d6138
[ 4077.510915]  ffff880ebb5173b0 ffff880ffa56baf8 ffff880ebb517410
ffff881016ce21c0
[ 4077.519202] Call Trace:
[ 4077.528752] [<ffffffffa06ed5ed>] ? btrfs_tree_lock+0xdd/0x2f0 [btrfs] 
[ 4077.536049]  [<ffffffff81053680>] ? wake_up_atomic_t+0x30/0x30
[ 4077.542574]  [<ffffffffa068cc1f>] ? btrfs_search_slot+0x79f/0xb10
[btrfs]
[ 4077.550171] [<ffffffffa06a5073>] ? btrfs_lookup_file_extent+0x33/0x40 
[btrfs]
[ 4077.558252] [<ffffffffa06c600b>] ? __btrfs_drop_extents+0x13b/0xdf0 
[btrfs]
[ 4077.566140] [<ffffffffa06fc9e2>] ? add_delayed_data_ref+0xe2/0x150 
[btrfs]
[ 4077.573928]  [<ffffffffa06fd629>] ?
btrfs_add_delayed_data_ref+0x149/0x1d0 [btrfs]
[ 4077.582399]  [<ffffffffa06cf3c0>] ? __set_extent_bit+0x4c0/0x5c0
[btrfs]
[ 4077.589896]  [<ffffffffa06b4a64>] ?
insert_reserved_file_extent.constprop.75+0xa4/0x320 [btrfs]
[ 4077.599632]  [<ffffffffa06b206d>] ? start_transaction+0x8d/0x470
[btrfs]
[ 4077.607134] [<ffffffffa06bab57>] ? btrfs_finish_ordered_io+0x2e7/0x600 
[btrfs]
[ 4077.615329]  [<ffffffff8104cbc2>] ? process_one_work+0x142/0x3d0
[ 4077.622043]  [<ffffffff8104d729>] ? worker_thread+0x109/0x3b0
[ 4077.628459] [<ffffffff8104d620>] ? manage_workers.isra.26+0x270/0x270 
[ 4077.635759]  [<ffffffff81052b0f>] ? kthread+0xaf/0xc0
[ 4077.641404] [<ffffffff81052a60>] ? kthread_create_on_node+0x110/0x110 
[ 4077.648696]  [<ffffffff814a9ac8>] ? ret_from_fork+0x58/0x90
[ 4077.654926] [<ffffffff81052a60>] ? kthread_create_on_node+0x110/0x110 

[ 4078.358087] kworker/u24:15  D ffff88107fcd0640     0 14436      2
0x00000000
[ 4078.365981] Workqueue: btrfs-endio-write btrfs_endio_write_helper
[btrfs]
[ 4078.373574]  ffff880ffa57fad0 0000000000000046 0000000000009000
ffff880ffa57ffd8
[ 4078.381864]  ffff880ffa57ffd8 ffff88103004d0a0 ffffffffa06ecb26
ffff88101a5d6138
[ 4078.390163]  ffff880fbeffc298 ffff880ffa57faf8 ffff880fbeffc2f8
ffff88103004d0a0
[ 4078.398466] Call Trace:
[ 4078.408019] [<ffffffffa06ed5ed>] ? btrfs_tree_lock+0xdd/0x2f0 [btrfs] 
[ 4078.415322]  [<ffffffff81053680>] ? wake_up_atomic_t+0x30/0x30
[ 4078.421844]  [<ffffffffa068cc1f>] ? btrfs_search_slot+0x79f/0xb10
[btrfs]
[ 4078.429438] [<ffffffffa06a5073>] ? btrfs_lookup_file_extent+0x33/0x40 
[btrfs]
[ 4078.437518] [<ffffffffa06c600b>] ? __btrfs_drop_extents+0x13b/0xdf0 
[btrfs]
[ 4078.445404] [<ffffffffa06fc9e2>] ? add_delayed_data_ref+0xe2/0x150 
[btrfs]
[ 4078.453194]  [<ffffffffa06fd629>] ?
btrfs_add_delayed_data_ref+0x149/0x1d0 [btrfs]
[ 4078.461663]  [<ffffffffa06cf3c0>] ? __set_extent_bit+0x4c0/0x5c0
[btrfs]
[ 4078.469161]  [<ffffffffa06b4a64>] ?
insert_reserved_file_extent.constprop.75+0xa4/0x320 [btrfs]
[ 4078.478893]  [<ffffffffa06b206d>] ? start_transaction+0x8d/0x470
[btrfs]
[ 4078.486388] [<ffffffffa06bab57>] ? btrfs_finish_ordered_io+0x2e7/0x600 
[btrfs]
[ 4078.494561]  [<ffffffff8104cbc2>] ? process_one_work+0x142/0x3d0
[ 4078.501278] [<ffffffff8104a507>] ? pwq_activate_delayed_work+0x27/0x40 
[ 4078.508673]  [<ffffffff8104d729>] ? worker_thread+0x109/0x3b0
[ 4078.515098] [<ffffffff8104d620>] ? manage_workers.isra.26+0x270/0x270 
[ 4078.522396]  [<ffffffff81052b0f>] ? kthread+0xaf/0xc0
[ 4078.528032] [<ffffffff81052a60>] ? kthread_create_on_node+0x110/0x110 
[ 4078.535325]  [<ffffffff814a9ac8>] ? ret_from_fork+0x58/0x90
[ 4078.541552] [<ffffffff81052a60>] ? kthread_create_on_node+0x110/0x110
[ 4079.355824] user-space-program D ffff88107fd30640 0 32020 1 
0x00000000
[ 4079.363716]  ffff880eae8eba10 0000000000000086 0000000000009000
ffff880eae8ebfd8
[ 4079.372003]  ffff880eae8ebfd8 ffff881016c162c0 ffffffffa06ecb26
ffff88101a5d6138
[ 4079.380294]  ffff880fbed4b4c8 ffff880eae8eba38 ffff880fbed4b528
ffff881016c162c0
[ 4079.388586] Call Trace:
[ 4079.398134] [<ffffffffa06ed595>] ? btrfs_tree_lock+0x85/0x2f0 [btrfs] 
[ 4079.405431]  [<ffffffff81053680>] ? wake_up_atomic_t+0x30/0x30
[ 4079.411955]  [<ffffffffa06876fb>] ? btrfs_lock_root_node+0x2b/0x40
[btrfs]
[ 4079.419644]  [<ffffffffa068ce83>] ? btrfs_search_slot+0xa03/0xb10
[btrfs]
[ 4079.427237] [<ffffffffa06aba52>] ? btrfs_buffer_uptodate+0x52/0x70 
[btrfs]
[ 4079.435041]  [<ffffffffa0689b60>] ?
generic_bin_search.constprop.38+0x80/0x190 [btrfs]
[ 4079.443897] [<ffffffffa068ea44>] ? btrfs_insert_empty_items+0x74/0xd0 
[btrfs]
[ 4079.451975]  [<ffffffffa072c443>] ? copy_items+0x128/0x850 [btrfs]
[ 4079.458890] [<ffffffffa072da10>] ? btrfs_log_inode+0x629/0xbf3 [btrfs] [ 4079.466292] [<ffffffffa06f34a1>] ? btrfs_log_inode_parent+0xc61/0xf30 
[btrfs]
[ 4079.474373] [<ffffffffa06f45a9>] ? btrfs_log_dentry_safe+0x59/0x80 
[btrfs]
[ 4079.482161] [<ffffffffa06c298d>] ? btrfs_sync_file+0x20d/0x330 [btrfs] 
[ 4079.489558]  [<ffffffff8112777c>] ? do_fsync+0x4c/0x80
[ 4079.495300]  [<ffffffff81127a0a>] ? SyS_fdatasync+0xa/0x10
[ 4079.501422]  [<ffffffff814a9b72>] ? system_call_fastpath+0x16/0x1b
[ 4079.508334] user-space-program D ffff88107fc30640 0 32021 1 
0x00000004
[ 4079.516226]  ffff880eae8efbf8 0000000000000086 0000000000009000
ffff880eae8effd8
[ 4079.524513]  ffff880eae8effd8 ffff881030279610 ffffffffa06ecb26
ffff88101a5d6138
[ 4079.532802]  ffff880ebb671d88 ffff880eae8efc20 ffff880ebb671de8
ffff881030279610
[ 4079.541092] Call Trace:
[ 4079.550642] [<ffffffffa06ed595>] ? btrfs_tree_lock+0x85/0x2f0 [btrfs] 
[ 4079.557941]  [<ffffffff81053680>] ? wake_up_atomic_t+0x30/0x30
[ 4079.564463]  [<ffffffffa068cc1f>] ? btrfs_search_slot+0x79f/0xb10
[btrfs]
[ 4079.572058]  [<ffffffffa06bb7d8>] ?
btrfs_truncate_inode_items+0x168/0xb90 [btrfs]
[ 4079.580526] [<ffffffffa06b04be>] ? join_transaction.isra.15+0x1e/0x3a0 
[btrfs]
[ 4079.588701]  [<ffffffffa06b206d>] ? start_transaction+0x8d/0x470
[btrfs]
[ 4079.596196]  [<ffffffffa0690ac6>] ? block_rsv_add_bytes+0x16/0x50
[btrfs]
[ 4079.603789] [<ffffffffa06bc2e9>] ? btrfs_truncate+0xe9/0x2e0 [btrfs] [ 4079.610994] [<ffffffffa06bd00b>] ? btrfs_setattr+0x30b/0x410 [btrfs] 
[ 4079.618197]  [<ffffffff81117c1c>] ? notify_change+0x1dc/0x680
[ 4079.624625]  [<ffffffff8123c8a4>] ? aa_path_perm+0xd4/0x160
[ 4079.630854]  [<ffffffff810f4fcb>] ? do_truncate+0x5b/0x90
[ 4079.636889]  [<ffffffff810f59fa>] ?
do_sys_ftruncate.constprop.15+0x10a/0x160
[ 4079.644869]  [<ffffffff8110d87b>] ? SyS_fcntl+0x5b/0x570
[ 4079.650805]  [<ffffffff814a9b72>] ? system_call_fastpath+0x16/0x1b
[ 4080.410607] user-space-program D ffff88107fc70640 0 32028 12639 
0x00000004
[ 4080.418489]  ffff880eaeccbbe0 0000000000000086 0000000000009000
ffff880eaeccbfd8
[ 4080.426778]  ffff880eaeccbfd8 ffff880f317ef1e0 ffffffffa06ecb26
ffff88101a5d6138
[ 4080.435067]  ffff880ef7e93928 ffff880f317ef1e0 ffff880eaeccbc08
ffff880f317ef1e0
[ 4080.443353] Call Trace:
[ 4080.452920] [<ffffffffa06ed15d>] ? btrfs_tree_read_lock+0xdd/0x190 
[btrfs]
[ 4080.460703]  [<ffffffff81053680>] ? wake_up_atomic_t+0x30/0x30
[ 4080.467225] [<ffffffffa06876bb>] ? btrfs_read_lock_root_node+0x2b/0x40 
[btrfs]
[ 4080.475400]  [<ffffffffa068cc81>] ? btrfs_search_slot+0x801/0xb10
[btrfs]
[ 4080.482994]  [<ffffffffa06b2df0>] ?
btrfs_clean_one_deleted_snapshot+0xe0/0xe0 [btrfs]
[ 4080.491857]  [<ffffffffa06a70a6>] ? btrfs_lookup_inode+0x26/0x90
[btrfs]
[ 4080.499353]  [<ffffffff810ec42f>] ? kmem_cache_alloc+0xaf/0xc0
[ 4080.505879]  [<ffffffffa06bd905>] ? btrfs_iget+0xd5/0x5d0 [btrfs]
[ 4080.512696]  [<ffffffffa06caf04>] ? btrfs_get_token_64+0x104/0x120
[btrfs]
[ 4080.520387] [<ffffffffa06f341f>] ? btrfs_log_inode_parent+0xbdf/0xf30 
[btrfs]
[ 4080.528469] [<ffffffffa06f45a9>] ? btrfs_log_dentry_safe+0x59/0x80 
[btrfs]
[ 4080.536258] [<ffffffffa06c298d>] ? btrfs_sync_file+0x20d/0x330 [btrfs] 
[ 4080.543657]  [<ffffffff8112777c>] ? do_fsync+0x4c/0x80
[ 4080.549399]  [<ffffffff81127a0a>] ? SyS_fdatasync+0xa/0x10
[ 4080.555534]  [<ffffffff814a9b72>] ? system_call_fastpath+0x16/0x1b

Signed-off-by: Robbie Ko <robbi...@synology.com>
---
 fs/btrfs/tree-log.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index ef9c55b..9913084 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -5213,6 +5213,7 @@ process_leaf:
                        if (di_key.type == BTRFS_ROOT_ITEM_KEY)
                                continue;

+                       btrfs_release_path(path);
di_inode = btrfs_iget(root->fs_info->sb, &di_key, 
                                              root, NULL);
                        if (IS_ERR(di_inode)) {
@@ -5222,13 +5223,12 @@ process_leaf:
if (btrfs_inode_in_log(di_inode, trans->transid)) 
{
                                iput(di_inode);
-                               continue;
+                               break;


Why the break instead of continue? This seems totally unrelated to the
deadlock on a leaf/node and incorrect.

thanks


                        }

                        ctx->log_new_dentries = false;
                        if (type == BTRFS_FT_DIR || type ==
BTRFS_FT_SYMLINK)
                                log_mode = LOG_INODE_ALL;
-                       btrfs_release_path(path);
                        ret = btrfs_log_inode(trans, root, di_inode,
                                              log_mode, 0, LLONG_MAX,
ctx);
                        if (!ret &&
--
1.9.1

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Filipe David Manana,

"People will forget what you said,
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 but people will never forget how you made them feel."


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