Re: [PATCH v3 00/21] DEPT(Dependency Tracker)
From: Byungchul Park
Date: Wed Mar 02 2022 - 19:18:41 EST
On Wed, Mar 02, 2022 at 04:53:41AM +0000, Hyeonggon Yoo wrote:
> On Wed, Mar 02, 2022 at 04:36:38AM +0000, Hyeonggon Yoo wrote:
> > On Mon, Feb 28, 2022 at 06:56:39PM +0900, Byungchul Park wrote:
> > > I didn't want to bother you so I was planning to send the next spin
> > > after making more progress. However, PATCH v2 reports too many false
> > > positives because Dept tracked the bit_wait_table[] wrong way - I
> > > apologize for that. So I decided to send PATCH v3 first before going
> > > further for those who want to run Dept for now.
> > >
> > > There might still be some false positives but not overwhelming.
> > >
> >
> > Hello Byungchul, I'm running DEPT v3 on my system
> > and I see report below.
> >
> > Looking at the kmemleak code and comment, I think
> > kmemleak tried to avoid lockdep recursive warning
> > but detected by DEPT?
> >
>
> Forgot to include another warning caused by DEPT.
>
> And comment below might be useful for debugging:
>
> in kmemleak.c:
> 43 * Locks and mutexes are acquired/nested in the following order:
> 44 *
> 45 * scan_mutex [-> object->lock] -> kmemleak_lock -> other_object->lock (SINGLE_DEPTH_NESTING)
> 46 *
> 47 * No kmemleak_lock and object->lock nesting is allowed outside scan_mutex
> 48 * regions.
>
> ===================================================
> DEPT: Circular dependency has been detected.
> 5.17.0-rc1+ #1 Tainted: G W
> ---------------------------------------------------
> summary
> ---------------------------------------------------
> *** DEADLOCK ***
>
> context A
> [S] __raw_spin_lock_irqsave(&object->lock:0)
> [W] __raw_spin_lock_irqsave(kmemleak_lock:0)
> [E] spin_unlock(&object->lock:0)
>
> context B
> [S] __raw_spin_lock_irqsave(kmemleak_lock:0)
> [W] _raw_spin_lock_nested(&object->lock:0)
> [E] spin_unlock(kmemleak_lock:0)
>
> [S]: start of the event context
> [W]: the wait blocked
> [E]: the event not reachable
Hi Hyeonggon,
Dept also allows the following scenario when an user guarantees that
each lock instance is different from another at a different depth:
lock A0 with depth
lock A1 with depth + 1
lock A2 with depth + 2
lock A3 with depth + 3
(and so on)
..
unlock A3
unlock A2
unlock A1
unlock A0
However, Dept does not allow the following scenario where another lock
class cuts in the dependency chain:
lock A0 with depth
lock B
lock A1 with depth + 1
lock A2 with depth + 2
lock A3 with depth + 3
(and so on)
..
unlock A3
unlock A2
unlock A1
unlock B
unlock A0
This scenario is clearly problematic. What do you think is going to
happen with another context running the following?
lock A1 with depth
lock B
lock A2 with depth + 1
lock A3 with depth + 2
(and so on)
..
unlock A3
unlock A2
unlock B
unlock A1
It's a deadlock. That's why Dept reports this case as a problem. Or am I
missing something?
Thanks,
Byungchul
> ---------------------------------------------------
> context A's detail
> ---------------------------------------------------
> context A
> [S] __raw_spin_lock_irqsave(&object->lock:0)
> [W] __raw_spin_lock_irqsave(kmemleak_lock:0)
> [E] spin_unlock(&object->lock:0)
>
> [S] __raw_spin_lock_irqsave(&object->lock:0):
> [<ffffffc00810302c>] scan_gray_list+0x84/0x13c
> stacktrace:
> dept_ecxt_enter+0x88/0xf4
> _raw_spin_lock_irqsave+0xf0/0x1c4
> scan_gray_list+0x84/0x13c
> kmemleak_scan+0x2d8/0x54c
> kmemleak_scan_thread+0xac/0xd4
> kthread+0xd4/0xe4
> ret_from_fork+0x10/0x20
>
> [W] __raw_spin_lock_irqsave(kmemleak_lock:0):
> [<ffffffc008102ebc>] scan_block+0x3c/0x128
> stacktrace:
> __dept_wait+0x8c/0xa4
> dept_wait+0x6c/0x88
> _raw_spin_lock_irqsave+0xb8/0x1c4
> scan_block+0x3c/0x128
> scan_gray_list+0xc4/0x13c
> kmemleak_scan+0x2d8/0x54c
> kmemleak_scan_thread+0xac/0xd4
> kthread+0xd4/0xe4
> ret_from_fork+0x10/0x20
>
> [E] spin_unlock(&object->lock:0):
> [<ffffffc008102ee0>] scan_block+0x60/0x128
>
> ---------------------------------------------------
> context B's detail
> ---------------------------------------------------
> context B
> [S] __raw_spin_lock_irqsave(kmemleak_lock:0)
> [W] _raw_spin_lock_nested(&object->lock:0)
> [E] spin_unlock(kmemleak_lock:0)
>
> [S] __raw_spin_lock_irqsave(kmemleak_lock:0):
> [<ffffffc008102ebc>] scan_block+0x3c/0x128
> stacktrace:
> dept_ecxt_enter+0x88/0xf4
> _raw_spin_lock_irqsave+0xf0/0x1c4
> scan_block+0x3c/0x128
> kmemleak_scan+0x19c/0x54c
> kmemleak_scan_thread+0xac/0xd4
> kthread+0xd4/0xe4
> ret_from_fork+0x10/0x20
>
> [W] _raw_spin_lock_nested(&object->lock:0):
> [<ffffffc008102f34>] scan_block+0xb4/0x128
> stacktrace:
> dept_wait+0x74/0x88
> _raw_spin_lock_nested+0xa8/0x1b0
> scan_block+0xb4/0x128
> kmemleak_scan+0x19c/0x54c
> kmemleak_scan_thread+0xac/0xd4
> kthread+0xd4/0xe4
> ret_from_fork+0x10/0x20
> [E] spin_unlock(kmemleak_lock:0):
> [<ffffffc008102ee0>] scan_block+0x60/0x128
> stacktrace:
> dept_event+0x7c/0xfc
> _raw_spin_unlock_irqrestore+0x8c/0x120
> scan_block+0x60/0x128
> kmemleak_scan+0x19c/0x54c
> kmemleak_scan_thread+0xac/0xd4
> kthread+0xd4/0xe4
> ret_from_fork+0x10/0x20
> ---------------------------------------------------
> information that might be helpful
> ---------------------------------------------------
> CPU: 1 PID: 38 Comm: kmemleak Tainted: G W 5.17.0-rc1+ #1
> 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+0x6c/0x70
> bfs+0xc0/0x168
> add_dep+0x88/0x11c
> add_wait+0x2d0/0x2dc
> __dept_wait+0x8c/0xa4
> dept_wait+0x6c/0x88
> _raw_spin_lock_irqsave+0xb8/0x1c4
> scan_block+0x3c/0x128
> scan_gray_list+0xc4/0x13c
> kmemleak_scan+0x2d8/0x54c
> kmemleak_scan_thread+0xac/0xd4
> kthread+0xd4/0xe4
> ret_from_fork+0x10/0x20
>
> > ===================================================
> > DEPT: Circular dependency has been detected.
> > 5.17.0-rc1+ #1 Tainted: G W
> > ---------------------------------------------------
> > summary
> > ---------------------------------------------------
> > *** AA DEADLOCK ***
> >
> > context A
> > [S] __raw_spin_lock_irqsave(&object->lock:0)
> > [W] _raw_spin_lock_nested(&object->lock:0)
> > [E] spin_unlock(&object->lock:0)
> >
> > [S]: start of the event context
> > [W]: the wait blocked
> > [E]: the event not reachable
> > ---------------------------------------------------
> > context A's detail
> > ---------------------------------------------------
> > context A
> > [S] __raw_spin_lock_irqsave(&object->lock:0)
> > [W] _raw_spin_lock_nested(&object->lock:0)
> > [E] spin_unlock(&object->lock:0)
> >
> > [S] __raw_spin_lock_irqsave(&object->lock:0):
> > [<ffffffc00810302c>] scan_gray_list+0x84/0x13c
> > stacktrace:
> > dept_ecxt_enter+0x88/0xf4
> > _raw_spin_lock_irqsave+0xf0/0x1c4
> > scan_gray_list+0x84/0x13c
> > kmemleak_scan+0x2d8/0x54c
> > kmemleak_scan_thread+0xac/0xd4
> > kthread+0xd4/0xe4
> > ret_from_fork+0x10/0x20
> >
> > [E] spin_unlock(&object->lock:0):
> > [<ffffffc008102ee0>] scan_block+0x60/0x128
> > ---------------------------------------------------
> > information that might be helpful
> > ---------------------------------------------------
> > CPU: 1 PID: 38 Comm: kmemleak Tainted: G W 5.17.0-rc1+ #1
> > 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
> > add_wait+0x2d0/0x2dc
> > __dept_wait+0x8c/0xa4
> > dept_wait+0x6c/0x88
> > _raw_spin_lock_nested+0xa8/0x1b0
> > scan_block+0xb4/0x128
> > scan_gray_list+0xc4/0x13c
> > kmemleak_scan+0x2d8/0x54c
> > kmemleak_scan_thread+0xac/0xd4
> > kthread+0xd4/0xe4
> > ret_from_fork+0x10/0x20
> >
> [...]
>
> --
> Thank you, You are awesome!
> Hyeonggon :-)