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
[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 :-)
