Hello,
On Sun 25-06-17 23:07:56, Alex Xu wrote:
> 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]
Can you still reproduce this?
> 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.
The two stacktraces that you've pasted show that we are waiting for buffer
lock - likely we have submitted the buffer for IO and are waiting for it to
complete. Together with the fact that switching to NOOP fixes the problem I
somewhat suspect that IO scheduler somehow fails to ever complete some IO -
added relevant people to CC.
Anyway if you can still reproduce, it would be good to get full output from
sysrq-w so that we can confirm that everything is blocked on waiting for IO
to complete.
> 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.
Honza
> [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 ]
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
