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.
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 :-)
