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Date:   Tue, 15 Mar 2022 12:04:07 +0000
From:   Hyeonggon Yoo <42.hyeyoo@gmail.com>
To:     Byungchul Park <byungchul.park@lge.com>
Cc:     torvalds@linux-foundation.org, damien.lemoal@opensource.wdc.com,
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Subject: Re: [PATCH v4 00/24] DEPT(Dependency Tracker)
Message-ID: <20220315120407.GA1471334@odroid>
References: <1646377603-19730-1-git-send-email-byungchul.park@lge.com>
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 <20220314065906.GA6255@X58A-UD3R>
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On Mon, Mar 14, 2022 at 03:59:06PM +0900, Byungchul Park wrote:
> On Sat, Mar 12, 2022 at 01:53:26AM +0000, Hyeonggon Yoo wrote:
> > On Fri, Mar 04, 2022 at 04:06:19PM +0900, Byungchul Park wrote:
> > > Hi Linus and folks,
> > > 
> > > I've been developing a tool for detecting deadlock possibilities by
> > > tracking wait/event rather than lock(?) acquisition order to try to
> > > cover all synchonization machanisms. It's done on v5.17-rc1 tag.
> > > 
> > > https://github.com/lgebyungchulpark/linux-dept/commits/dept1.14_on_v5.17-rc1
> > >
> > 
> > Small feedback unrelated to thread:
> > I'm not sure "Need to expand the ring buffer" is something to call
> > WARN(). Is this stack trace useful for something?
> 
> Yeah. It seems to happen too often. I won't warn it. Thanks.

Thanks!

> > ========
> > 
> > Hello Byungchul. These are two warnings of DEPT on system.
> > Both cases look similar.
> > 
> > In what case DEPT says (unknown)?
> > I'm not sure we can properly debug this.
> > 
> > ===================================================
> > DEPT: Circular dependency has been detected.
> > 5.17.0-rc1+ #3 Tainted: G        W        
> > ---------------------------------------------------
> > summary
> > ---------------------------------------------------
> > *** AA DEADLOCK ***
> > 
> > context A
> >     [S] (unknown)(&vfork:0)
> >     [W] wait_for_completion_killable(&vfork:0)
> >     [E] complete(&vfork:0)
> 
> All the reports look like having to do with kernel_clone(). I need to
> check it more. Thank you very much.
> 
> You are awesome, Hyeonggon.
>

Thank you. Let me know if there is something I can help!

> Thank you,
> Byungchul
> 
> > [S]: start of the event context
> > [W]: the wait blocked
> > [E]: the event not reachable
> > ---------------------------------------------------
> > context A's detail
> > ---------------------------------------------------
> > context A
> >     [S] (unknown)(&vfork:0)
> >     [W] wait_for_completion_killable(&vfork:0)
> >     [E] complete(&vfork:0)
> > 
> > [S] (unknown)(&vfork:0):
> > (N/A)
> > 
> > [W] wait_for_completion_killable(&vfork:0):
> > [<ffffffc00802204c>] kernel_clone+0x25c/0x2b8
> > stacktrace:
> >       dept_wait+0x74/0x88
> >       wait_for_completion_killable+0x60/0xa0
> >       kernel_clone+0x25c/0x2b8
> >       __do_sys_clone+0x5c/0x74
> >       __arm64_sys_clone+0x18/0x20
> >       invoke_syscall.constprop.0+0x78/0xc4
> >       do_el0_svc+0x98/0xd0
> >       el0_svc+0x44/0xe4
> >       el0t_64_sync_handler+0xb0/0x12c
> >       el0t_64_sync+0x158/0x15c
> > 
> > [E] complete(&vfork:0):
> > [<ffffffc00801f49c>] mm_release+0x7c/0x90
> > stacktrace:
> >       dept_event+0xe0/0x100
> >       complete+0x48/0x98
> >       mm_release+0x7c/0x90
> >       exit_mm_release+0xc/0x14
> >       do_exit+0x1b4/0x81c
> >       do_group_exit+0x30/0x9c
> >       __wake_up_parent+0x0/0x24
> >       invoke_syscall.constprop.0+0x78/0xc4
> >       do_el0_svc+0x98/0xd0
> >       el0_svc+0x44/0xe4
> >       el0t_64_sync_handler+0xb0/0x12c
> >       el0t_64_sync+0x158/0x15c
> > ---------------------------------------------------
> > information that might be helpful
> > ---------------------------------------------------
> > CPU: 6 PID: 229 Comm: start-stop-daem Tainted: G        W         5.17.0-rc1+ #3
> > Hardware name: linux,dummy-virt (DT)
> > Call trace:
> >  dump_backtrace.part.0+0x9c/0xc4
> >  show_stack+0x14/0x28
> >  dump_stack_lvl+0x9c/0xcc
> >  dump_stack+0x14/0x2c
> >  print_circle+0x2d4/0x438
> >  cb_check_dl+0x44/0x70
> >  bfs+0x60/0x168
> >  add_dep+0x88/0x11c
> >  do_event.constprop.0+0x19c/0x2c0
> >  dept_event+0xe0/0x100
> >  complete+0x48/0x98
> >  mm_release+0x7c/0x90
> >  exit_mm_release+0xc/0x14
> >  do_exit+0x1b4/0x81c
> >  do_group_exit+0x30/0x9c
> >  __wake_up_parent+0x0/0x24
> >  invoke_syscall.constprop.0+0x78/0xc4
> >  do_el0_svc+0x98/0xd0
> >  el0_svc+0x44/0xe4
> >  el0t_64_sync_handler+0xb0/0x12c
> >  el0t_64_sync+0x158/0x15c
> > 
> > 
> > 
> > 
> > ===================================================
> > DEPT: Circular dependency has been detected.
> > 5.17.0-rc1+ #3 Tainted: G        W        
> > ---------------------------------------------------
> > summary
> > ---------------------------------------------------
> > *** AA DEADLOCK ***
> > 
> > context A
> >     [S] (unknown)(&try_completion:0)
> >     [W] wait_for_completion_timeout(&try_completion:0)
> >     [E] complete(&try_completion:0)
> > 
> > [S]: start of the event context
> > [W]: the wait blocked
> > [E]: the event not reachable
> > ---------------------------------------------------
> > context A's detail
> > ---------------------------------------------------
> > context A
> >     [S] (unknown)(&try_completion:0)
> >     [W] wait_for_completion_timeout(&try_completion:0)
> >     [E] complete(&try_completion:0)
> > 
> > [S] (unknown)(&try_completion:0):
> > (N/A)
> > 
> > [W] wait_for_completion_timeout(&try_completion:0):
> > [<ffffffc008166bf4>] kunit_try_catch_run+0xb4/0x160
> > stacktrace:
> >       dept_wait+0x74/0x88
> >       wait_for_completion_timeout+0x64/0xa0
> >       kunit_try_catch_run+0xb4/0x160
> >       kunit_test_try_catch_successful_try_no_catch+0x3c/0x98
> >       kunit_try_run_case+0x9c/0xa0
> >       kunit_generic_run_threadfn_adapter+0x1c/0x28
> >       kthread+0xd4/0xe4
> >       ret_from_fork+0x10/0x20
> > 
> > [E] complete(&try_completion:0):
> > [<ffffffc00803dce4>] kthread_complete_and_exit+0x18/0x20
> > stacktrace:
> >       dept_event+0xe0/0x100
> >       complete+0x48/0x98
> >       kthread_complete_and_exit+0x18/0x20
> >       kunit_try_catch_throw+0x0/0x1c
> >       kthread+0xd4/0xe4
> >       ret_from_fork+0x10/0x20
> > 
> > ---------------------------------------------------
> > information that might be helpful
> > ---------------------------------------------------
> > CPU: 15 PID: 132 Comm: kunit_try_catch Tainted: G        W         5.17.0-rc1+ #3
> > Hardware name: linux,dummy-virt (DT)
> > Call trace:
> >  dump_backtrace.part.0+0x9c/0xc4
> >  show_stack+0x14/0x28
> >  dump_stack_lvl+0x9c/0xcc
> >  dump_stack+0x14/0x2c
> >  print_circle+0x2d4/0x438
> >  cb_check_dl+0x44/0x70
> >  bfs+0x60/0x168
> >  add_dep+0x88/0x11c
> >  do_event.constprop.0+0x19c/0x2c0
> >  dept_event+0xe0/0x100
> >  complete+0x48/0x98
> >  kthread_complete_and_exit+0x18/0x20
> >  kunit_try_catch_throw+0x0/0x1c
> >  kthread+0xd4/0xe4
> >  ret_from_fork+0x10/0x20
> 
> 
> > -- 
> > Thank you, You are awesome!
> > Hyeonggon :-)