possible circular locking dependency detected [was: linux-next: Tree for Aug 22]

Commit Message

Sergey Senozhatsky Aug. 30, 2017, 5:20 a.m. UTC

On (08/23/17 09:03), Byungchul Park wrote:
[..]
> > Byungchul, did you add the crosslock checks to lockdep? Can you have a look at
> > the above report? That report namely doesn't make sense to me.
> 
> The report is talking about the following lockup:
> 
> A work in a worker                     A task work on exit to user
> ------------------                     ---------------------------
> mutex_lock(&bdev->bd_mutex)
>                                        mutext_lock(&bdev->bd_mutex)
> blk_execute_rq()
>    wait_for_completion_io_timeout(&A)
>                                        complete(&A)
> 
[..]
> To Peterz,
> 
> Anyway I wanted to avoid lockdep reports in the case using a timeout
> interface. Do you think it's still worth reporting the kind of lockup?
> I'm ok if you do.

Byungchul, a quick question.
have you measured the performance impact? somehow my linux-next is
notably slower than earlier 4.13 linux-next. (e.g. scrolling in vim
is irritatingly slow)


`time dmesg' shows some difference, but probably that's not a good
test.

	!LOCKDEP	LOCKDEP		LOCKDEP -CROSSRELEASE -COMPLETIONS
	real 0m0.661s	0m2.290s	0m1.920s
	user 0m0.010s	0m0.105s	0m0.000s
	sys  0m0.636s	0m2.224s	0m1.888s

anyone else "sees"/"can confirm" the slow down?


it gets back to "usual normal" when I disable CROSSRELEASE and COMPLETIONS.

---


---

	-ss

Comments

Byungchul Park Aug. 30, 2017, 5:43 a.m. UTC | #1

On Wed, Aug 30, 2017 at 02:20:37PM +0900, Sergey Senozhatsky wrote:
> Byungchul, a quick question.

Hello Sergey,

> have you measured the performance impact? somehow my linux-next is

Yeah, it might have performance impact inevitably.

> notably slower than earlier 4.13 linux-next. (e.g. scrolling in vim
> is irritatingly slow)

To Ingo,

I cannot decide if we have to roll back CONFIG_LOCKDEP_CROSSRELEASE
dependency on CONFIG_PROVE_LOCKING in Kconfig. With them enabled,
lockdep detection becomes strong but has performance impact. But,
it's anyway a debug option so IMHO we don't have to take case of the
performance impact. Please let me know your decision.

> `time dmesg' shows some difference, but probably that's not a good
> test.
> 
> 	!LOCKDEP	LOCKDEP		LOCKDEP -CROSSRELEASE -COMPLETIONS
> 	real 0m0.661s	0m2.290s	0m1.920s
> 	user 0m0.010s	0m0.105s	0m0.000s
> 	sys  0m0.636s	0m2.224s	0m1.888s
> 
> anyone else "sees"/"can confirm" the slow down?
> 
> 
> it gets back to "usual normal" when I disable CROSSRELEASE and COMPLETIONS.
> 
> ---
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index b19c491cbc4e..cdc30ef81c5e 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1091,8 +1091,6 @@ config PROVE_LOCKING
>         select DEBUG_MUTEXES
>         select DEBUG_RT_MUTEXES if RT_MUTEXES
>         select DEBUG_LOCK_ALLOC
> -       select LOCKDEP_CROSSRELEASE
> -       select LOCKDEP_COMPLETIONS
>         select TRACE_IRQFLAGS
>         default n
>         help
> 
> ---
> 
> 	-ss

Sergey Senozhatsky Aug. 30, 2017, 6:15 a.m. UTC | #2

Hi,

On (08/30/17 14:43), Byungchul Park wrote:
[..]
> > notably slower than earlier 4.13 linux-next. (e.g. scrolling in vim
> > is irritatingly slow)
> 
> To Ingo,
> 
> I cannot decide if we have to roll back CONFIG_LOCKDEP_CROSSRELEASE
> dependency on CONFIG_PROVE_LOCKING in Kconfig. With them enabled,
> lockdep detection becomes strong but has performance impact. But,
> it's anyway a debug option so IMHO we don't have to take case of the
> performance impact. Please let me know your decision.

well, I expected it :)

I've been running lockdep enabled kernels for years, and was OK with
the performance. but now it's just too much and I'm looking at disabling
lockdep.

a more relevant test -- compilation of a relatively small project

  LOCKDEP -CROSSRELEASE -COMPLETIONS     LOCKDEP +CROSSRELEASE +COMPLETIONS

   real    1m23.722s                      real    2m9.969s
   user    4m11.300s                      user    4m15.458s
   sys     0m49.386s                      sys     2m3.594s


you don't want to know how much time now it takes to recompile the
kernel ;)

	-ss

Patch

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b19c491cbc4e..cdc30ef81c5e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1091,8 +1091,6 @@  config PROVE_LOCKING
        select DEBUG_MUTEXES
        select DEBUG_RT_MUTEXES if RT_MUTEXES
        select DEBUG_LOCK_ALLOC
-       select LOCKDEP_CROSSRELEASE
-       select LOCKDEP_COMPLETIONS
        select TRACE_IRQFLAGS
        default n
        help