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Date:   Wed, 16 Mar 2022 09:30:02 +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: <YjGuGmdiZCpRt98n@ip-172-31-19-208.ap-northeast-1.compute.internal>
References: <1646377603-19730-1-git-send-email-byungchul.park@lge.com>
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 <20220316043212.GA5715@X58A-UD3R>
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On Wed, Mar 16, 2022 at 01:32:13PM +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?
> > ========
> > 
> > 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 (:
>

Hi Byungchul.

on dept1.18_on_v5.17-rc7, the kernel_clone() warning has gone.
There is one warning remaining on my system:

It warns when running kunit-try-catch-test testcase.

===================================================
DEPT: Circular dependency has been detected.
5.17.0-rc7+ #4 Not tainted
---------------------------------------------------
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):
kunit_try_catch_run (lib/kunit/try-catch.c:78 (discriminator 1)) 
stacktrace:
dept_wait (kernel/dependency/dept.c:2149) 
wait_for_completion_timeout (kernel/sched/completion.c:119 (discriminator 4) kernel/sched/completion.c:165 (discriminator 4)) 
kunit_try_catch_run (lib/kunit/try-catch.c:78 (discriminator 1)) 
kunit_test_try_catch_successful_try_no_catch (lib/kunit/kunit-test.c:43) 
kunit_try_run_case (lib/kunit/test.c:333 lib/kunit/test.c:374) 
kunit_generic_run_threadfn_adapter (lib/kunit/try-catch.c:30) 
kthread (kernel/kthread.c:379) 
ret_from_fork (arch/arm64/kernel/entry.S:757)

[E] complete(&try_completion:0):
kthread_complete_and_exit (kernel/kthread.c:327) 
stacktrace:
dept_event (kernel/dependency/dept.c:2376 (discriminator 2)) 
complete (kernel/sched/completion.c:33 (discriminator 4)) 
kthread_complete_and_exit (kernel/kthread.c:327) 
kunit_try_catch_throw (lib/kunit/try-catch.c:18) 
kthread (kernel/kthread.c:379) 
ret_from_fork (arch/arm64/kernel/entry.S:757) 

---------------------------------------------------
information that might be helpful
---------------------------------------------------
Hardware name: linux,dummy-virt (DT)
Call trace:
dump_backtrace.part.0 (arch/arm64/kernel/stacktrace.c:186) 
show_stack (arch/arm64/kernel/stacktrace.c:193) 
dump_stack_lvl (lib/dump_stack.c:107 (discriminator 4)) 
dump_stack (lib/dump_stack.c:114) 
print_circle (./arch/arm64/include/asm/atomic_ll_sc.h:112 ./arch/arm64/include/asm/atomic.h:30 ./include/linux/atomic/atomic-arch-fallback.h:511 ./include/linux/atomic/atomic-instrumented.h:258 kernel/dependency/dept.c:140 kernel/dependency/dept.c:748) 
cb_check_dl (kernel/dependency/dept.c:1083 kernel/dependency/dept.c:1064) 
bfs (kernel/dependency/dept.c:833) 
add_dep (kernel/dependency/dept.c:1409) 
do_event (kernel/dependency/dept.c:175 kernel/dependency/dept.c:1644) 
dept_event (kernel/dependency/dept.c:2376 (discriminator 2)) 
complete (kernel/sched/completion.c:33 (discriminator 4)) 
kthread_complete_and_exit (kernel/kthread.c:327) 
kunit_try_catch_throw (lib/kunit/try-catch.c:18) 
kthread (kernel/kthread.c:379) 
ret_from_fork (arch/arm64/kernel/entry.S:757)

-- 
Thank you, You are awesome!
Hyeonggon :-)

> 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 :-)