Re: [PATCH v3 00/21] DEPT(Dependency Tracker)

[Byungchul Park <byungchul.park@lge.com>]

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?
> 
> ===================================================
> 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

[W]'s stack trace is missed. But I guess this issue is the same issue of
what you reported following this one. We can discuss this issue on the
other report's thread.

Thanks,
Byunghcul

> [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
> 
> > ---
> > 
> > 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
> >
> [...]
> > 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:
> > 
> > 	0. To make it more stable.
> > 	1. To separates Dept from Lockdep.
> > 	2. To improves performance in terms of time and space.
> > 	3. To use Dept as a dependency engine for Lockdep.
> > 	4. To add any missing tags of wait/event in the kernel.
> > 	5. To deduplicate stack trace.
> > 
> > How to interpret reports:
> > 
> > 	1. E(event) in each context cannot be triggered because of the
> > 	   W(wait) that cannot be woken.
> > 	2. The stack trace helping find the problematic code is located
> > 	   in each conext's detail.
> > 
> > Thanks,
> > Byungchul
> > 
> > ---
> > 
> > Changes from v2:
> > 
> > 	1. Disable Dept on bit_wait_table[] in sched/wait_bit.c
> > 	   reporting a lot of false positives, which is my fault.
> > 	   Wait/event for bit_wait_table[] should've been tagged in a
> > 	   higher layer for better work, which is a future work.
> > 	   (feedback from Jan Kara)
> > 	2. Disable Dept on crypto_larval's completion to prevent a false
> > 	   positive.
> > 
> > Changes from v1:
> > 
> > 	1. Fix coding style and typo. (feedback from Steven)
> > 	2. Distinguish each work context from another in workqueue.
> > 	3. Skip checking lock acquisition with nest_lock, which is about
> > 	   correct lock usage that should be checked by Lockdep.
> > 
> > Changes from RFC:
> > 
> > 	1. Prevent adding a wait tag at prepare_to_wait() but __schedule().
> > 	   (feedback from Linus and Matthew)
> > 	2. Use try version at lockdep_acquire_cpus_lock() annotation.
> > 	3. Distinguish each syscall context from another.
> [ ... ] 
> 
> -- 
> Thank you, You are awesome!
> Hyeonggon :-)