From: Byungchul Park <byungchul.park@lge.com>
To: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: torvalds@linux-foundation.org, damien.lemoal@opensource.wdc.com,
linux-ide@vger.kernel.org, adilger.kernel@dilger.ca,
linux-ext4@vger.kernel.org, mingo@redhat.com,
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will@kernel.org, tglx@linutronix.de, rostedt@goodmis.org,
joel@joelfernandes.org, sashal@kernel.org,
daniel.vetter@ffwll.ch, chris@chris-wilson.co.uk,
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tytso@mit.edu, willy@infradead.org, david@fromorbit.com,
amir73il@gmail.com, bfields@fieldses.org,
gregkh@linuxfoundation.org, kernel-team@lge.com,
linux-mm@kvack.org, akpm@linux-foundation.org, mhocko@kernel.org,
minchan@kernel.org, hannes@cmpxchg.org, vdavydov.dev@gmail.com,
sj@kernel.org, jglisse@redhat.com, dennis@kernel.org,
cl@linux.com, penberg@kernel.org, rientjes@google.com,
vbabka@suse.cz, ngupta@vflare.org, linux-block@vger.kernel.org,
paolo.valente@linaro.org, josef@toxicpanda.com,
linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
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dri-devel@lists.freedesktop.org, airlied@linux.ie,
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hamohammed.sa@gmail.com
Subject: Re: [PATCH v3 00/21] DEPT(Dependency Tracker)
Date: Thu, 3 Mar 2022 18:48:24 +0900 [thread overview]
Message-ID: <20220303094824.GA24977@X58A-UD3R> (raw)
In-Reply-To: <YiB2SZFzgBEcywgg@ip-172-31-19-208.ap-northeast-1.compute.internal>
On Thu, Mar 03, 2022 at 08:03:21AM +0000, Hyeonggon Yoo wrote:
> On Thu, Mar 03, 2022 at 09:18:13AM +0900, Byungchul Park wrote:
> > 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
Look at this. Dept allows object->lock -> other_object->lock (with a
different depth using *_lock_nested()) so won't report it.
> > 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?
> >
>
> First of all, I want to say I'm not expert at locking primitives.
> I may be wrong.
It's okay. Thanks anyway for your feedback.
> > > 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.
>
> lock order in kmemleak is described above.
>
> and DEPT detects two cases as deadlock:
>
> 1) object->lock -> other_object->lock
It's not a deadlock *IF* two have different depth using *_lock_nested().
Dept also allows this case. So Dept wouldn't report it.
> 2) object->lock -> kmemleak_lock, kmemleak_lock -> other_object->lock
But this usage is risky. I already explained it in the mail you replied
to. I copied it. See the below.
context A
> > 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
...
context B
> > 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
where Ax : object->lock, B : kmemleak_lock.
A deadlock might occur if the two contexts run at the same time.
> And in kmemleak case, 1) and 2) is not possible because it must hold
> scan_mutex first.
This is another issue. Let's focus on whether the order is okay for now.
> I think the author of kmemleak intended lockdep to treat object->lock
> and other_object->lock as different class, using raw_spin_lock_nested().
Yes. The author meant to assign a different class according to its depth
using a Lockdep API. Strictly speaking, those are the same class anyway
but we assign a different class to each depth to avoid Lockdep splats
*IF* the user guarantees the nesting lock usage is safe, IOW, guarantees
each lock instance is different at a different depth.
I was fundamentally asking you... so... is the nesting lock usage safe
for real? I hope you distinguish between the safe case and the risky
case when *_lock_nested() is involved. Thoughts?
Thanks,
Byungchul
> Am I missing something?
>
> Thanks.
>
> > 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 :-)
>
> --
> Thank you, You are awesome!
> Hyeonggon :-)
next prev parent reply other threads:[~2022-03-03 9:48 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-28 9:56 [PATCH v3 00/21] DEPT(Dependency Tracker) Byungchul Park
2022-02-28 9:56 ` [PATCH v3 01/21] llist: Move llist_{head,node} definition to types.h Byungchul Park
2022-02-28 9:56 ` [PATCH v3 02/21] dept: Implement Dept(Dependency Tracker) Byungchul Park
2022-02-28 9:56 ` [PATCH v3 03/21] dept: Embed Dept data in Lockdep Byungchul Park
2022-02-28 9:56 ` [PATCH v3 04/21] dept: Add a API for skipping dependency check temporarily Byungchul Park
2022-02-28 9:56 ` [PATCH v3 05/21] dept: Apply Dept to spinlock Byungchul Park
2022-02-28 9:56 ` [PATCH v3 06/21] dept: Apply Dept to mutex families Byungchul Park
2022-02-28 9:56 ` [PATCH v3 07/21] dept: Apply Dept to rwlock Byungchul Park
2022-02-28 9:56 ` [PATCH v3 08/21] dept: Apply Dept to wait_for_completion()/complete() Byungchul Park
2022-02-28 9:56 ` [PATCH v3 09/21] dept: Apply Dept to seqlock Byungchul Park
2022-02-28 9:56 ` [PATCH v3 10/21] dept: Apply Dept to rwsem Byungchul Park
2022-02-28 9:56 ` [PATCH v3 11/21] dept: Add proc knobs to show stats and dependency graph Byungchul Park
2022-02-28 9:56 ` [PATCH v3 12/21] dept: Introduce split map concept and new APIs for them Byungchul Park
2022-02-28 9:56 ` [PATCH v3 13/21] dept: Apply Dept to wait/event of PG_{locked,writeback} Byungchul Park
2022-02-28 9:56 ` [PATCH v3 14/21] dept: Apply SDT to swait Byungchul Park
2022-02-28 9:56 ` [PATCH v3 15/21] dept: Apply SDT to wait(waitqueue) Byungchul Park
2022-02-28 9:56 ` [PATCH v3 16/21] locking/lockdep, cpu/hotplus: Use a weaker annotation in AP thread Byungchul Park
2022-02-28 9:56 ` [PATCH v3 17/21] dept: Distinguish each syscall context from another Byungchul Park
2022-02-28 9:56 ` [PATCH v3 18/21] dept: Distinguish each work " Byungchul Park
2022-02-28 9:56 ` [PATCH v3 19/21] dept: Disable Dept within the wait_bit layer by default Byungchul Park
2022-02-28 9:56 ` [PATCH v3 20/21] dept: Add nocheck version of init_completion() Byungchul Park
2022-02-28 9:57 ` [PATCH v3 21/21] dept: Disable Dept on struct crypto_larval's completion for now Byungchul Park
2022-03-02 4:36 ` [PATCH v3 00/21] DEPT(Dependency Tracker) Hyeonggon Yoo
2022-03-02 4:53 ` Hyeonggon Yoo
2022-03-03 0:18 ` Byungchul Park
2022-03-03 8:03 ` Hyeonggon Yoo
2022-03-03 9:48 ` Byungchul Park [this message]
2022-03-03 12:38 ` Hyeonggon Yoo
2022-03-04 0:28 ` Byungchul Park
2022-03-03 2:22 ` Byungchul Park
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