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Date:   Wed, 16 Mar 2022 13:32:13 +0900
From:   Byungchul Park <byungchul.park@lge.com>
To:     Hyeonggon Yoo <42.hyeyoo@gmail.com>
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Subject: Re: [PATCH v4 00/24] DEPT(Dependency Tracker)
Message-ID: <20220316043212.GA5715@X58A-UD3R>
References: <1646377603-19730-1-git-send-email-byungchul.park@lge.com>
 <Yiv9Fn4kcRbXJLmu@ip-172-31-19-208.ap-northeast-1.compute.internal>
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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?
> ========
> 
> Hello Byungchul. These are two warnings of DEPT on system.

Hi Hyeonggon,

Could you run scripts/decode_stacktrace.sh and share the result instead
of the raw format below if the reports still appear with PATCH v5? It'd
be appreciated (:

https://lkml.org/lkml/2022/3/15/1277
(or https://github.com/lgebyungchulpark/linux-dept/commits/dept1.18_on_v5.17-rc7)

Thank you very much!

--
Byungchul

> 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)
> 
> [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
> 
> 
> > Benifit:
> > 
> > 	0. Works with all lock primitives.
> > 	1. Works with wait_for_completion()/complete().
> > 	2. Works with 'wait' on PG_locked.
> > 	3. Works with 'wait' on PG_writeback.
> > 	4. Works with swait/wakeup.
> > 	5. Works with waitqueue.
> > 	6. Multiple reports are allowed.
> > 	7. Deduplication control on multiple reports.
> > 	8. Withstand false positives thanks to 6.
> > 	9. Easy to tag any wait/event.
> > 
> > Future work:
> 
> [...]
> 
> > -- 
> > 1.9.1
> > 
> 
> -- 
> Thank you, You are awesome!
> Hyeonggon :-)