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Subjectbfq/ext4 disk IO hangs forever on resume
Hi,

I get hangs when resuming when using bfq-mq with ext4 on 4.12-rc6+
(currently a4fd8b3accf43d407472e34403d4b0a4df5c0e71).

Steps to reproduce:
1. boot computer
2. systemctl suspend
3. wait few seconds
4. press power button
5. type "ls" into console or SSH or do anything that does disk IO

Expected results:
Command is executed.

Actual results:
Command hangs.

lockdep has no comments, but sysrq-d shows that i_mutex_dir_key and
jbd2_handle are held by multiple processes, leading me to suspect that
ext4 is at least partially involved. [0]

sysrq-w lists many blocked processes [1]

This happens consistently, every time I resume the system from
suspend-to-RAM using this configuration. Switching to noop IO scheduler
makes it stop happening. I haven't tried switching filesystems yet.

I can do more debugging (enable KASAN or whatever), but usually when I
bother doing that I find someone has already sent a patch for the issue.

Please CC me on replies.

Cheers,
Alex.

[0]

4 locks held by systemd/384:
#0: (sb_writers#3){.+.+.+}, at: [<ffffffff811b0e5f>] mnt_want_write+0x1f/0x50
#1: (&type->i_mutex_dir_key/1){+.+.+.}, at: [<ffffffff8119b7ce>] do_rmdir+0x15e/0x1e0
#2: (&type->i_mutex_dir_key){++++++}, at: [<ffffffff81195ee0>] vfs_rmdir+0x50/0x130
#3: (jbd2_handle){++++..}, at: [<ffffffff8124f17f>] start_this_handle+0xff/0x430
4 locks held by syncthing/279:
#0: (&f->f_pos_lock){+.+.+.}, at: [<ffffffff811ade1e>] __fdget_pos+0x3e/0x50
#1: (sb_writers#3){.+.+.+}, at: [<ffffffff8118b04c>] vfs_write+0x17c/0x1d0
#2: (&sb->s_type->i_mutex_key#9){+.+.+.}, at: [<ffffffff81217977>] ext4_file_write_iter+0x57/0x350
#3: (jbd2_handle){++++..}, at: [<ffffffff8124f17f>] start_this_handle+0xff/0x430
2 locks held by zsh/238:
#0: (&tty->ldisc_sem){++++.+}, at: [<ffffffff816fbeaf>] ldsem_down_read+0x1f/0x30
#1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff8134fbb0>] n_tty_read+0xb0/0x8b0
2 locks held by sddm-greeter/267:
#0: (sb_writers#3){.+.+.+}, at: [<ffffffff811b0e5f>] mnt_want_write+0x1f/0x50
#1: (&type->i_mutex_dir_key){++++++}, at: [<ffffffff8119a698>] path_openat+0x2d8/0xa10
2 locks held by kworker/u16:28/330:
#0: ("events_unbound"){.+.+.+}, at: [<ffffffff810a1ef3>] process_one_work+0x1c3/0x420
#1: ((&entry->work)){+.+.+.}, at: [<ffffffff810a1ef3>] process_one_work+0x1c3/0x420
1 lock held by zsh/382:
#0: (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff81192570>] prepare_bprm_creds+0x30/0x70

[1]

task PC stack pid father
systemd D 0 384 0 0x00000000
Call Trace:
__schedule+0x295/0x7c0
? bit_wait+0x50/0x50
? bit_wait+0x50/0x50
schedule+0x31/0x80
io_schedule+0x11/0x40
bit_wait_io+0xc/0x50
__wait_on_bit+0x53/0x80
? bit_wait+0x50/0x50
out_of_line_wait_on_bit+0x6e/0x80
? autoremove_wake_function+0x30/0x30
do_get_write_access+0x20b/0x420
jbd2_journal_get_write_access+0x2c/0x60
__ext4_journal_get_write_access+0x55/0xa0
ext4_delete_entry+0x8c/0x140
? __ext4_journal_start_sb+0x4e/0xa0
ext4_rmdir+0x114/0x250
vfs_rmdir+0x6e/0x130
do_rmdir+0x1a3/0x1e0
SyS_unlinkat+0x1d/0x30
entry_SYSCALL_64_fastpath+0x18/0xad
jbd2/sda1-8 D 0 81 2 0x00000000
Call Trace:
__schedule+0x295/0x7c0
? bit_wait+0x50/0x50
schedule+0x31/0x80
io_schedule+0x11/0x40
bit_wait_io+0xc/0x50
__wait_on_bit+0x53/0x80
? bit_wait+0x50/0x50
out_of_line_wait_on_bit+0x6e/0x80
? autoremove_wake_function+0x30/0x30
__wait_on_buffer+0x2d/0x30
jbd2_journal_commit_transaction+0xe6a/0x1700
kjournald2+0xc8/0x270
? kjournald2+0xc8/0x270
? wake_atomic_t_function+0x50/0x50
kthread+0xfe/0x130
? commit_timeout+0x10/0x10
? kthread_create_on_node+0x40/0x40
ret_from_fork+0x27/0x40
[ more processes follow, some different tracebacks ]

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