All of lore.kernel.org
 help / color / mirror / Atom feed
From: Ingo Molnar <mingo@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"byungchul.park@lge.com" <byungchul.park@lge.com>,
	"kernel-team@lge.com" <kernel-team@lge.com>
Subject: Re: [PATCH v2 2/3] lockdep: Remove BROKEN flag of LOCKDEP_CROSSRELEASE
Date: Fri, 20 Oct 2017 09:30:50 +0200	[thread overview]
Message-ID: <20171020073050.nyaqynbbkeltr7iq@gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1710192233130.2054@nanos>


* Thomas Gleixner <tglx@linutronix.de> wrote:

> That would just make the door open for evading lockdep. This has been
> discussed when lockdep was introduced and with a lot of other 'annoying'
> debug features we've seen the same discussion happening.
> 
> When they get introduced the number of real issues and false positives is
> high, but once the dust settles it's just business as usual and the overall
> code quality improves and the number of hard to decode problems shrinks.

Yes, also note that it's typical that the proportion of false positives 
*increases* once a lock debugging feature enters a more mature period of its 
existence, because real deadlocks tend to be fixed at the development stage 
without us ever seeing them.

I.e. for every lockdep-debugged bug fixed upstream I'm pretty sure there are at 
least 10 times as many bugs that were fixed in earlier stages of development, 
without ever hitting the upstream kernel. At least that's the rough proportion
for locking bugs I introduce ;-)

So even false positives are not a problem as long as their annotation improves the 
code or documents it better.

Thanks,

	Ingo

WARNING: multiple messages have this Message-ID (diff)
From: Ingo Molnar <mingo@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"byungchul.park@lge.com" <byungchul.park@lge.com>,
	"kernel-team@lge.com" <kernel-team@lge.com>
Subject: Re: [PATCH v2 2/3] lockdep: Remove BROKEN flag of LOCKDEP_CROSSRELEASE
Date: Fri, 20 Oct 2017 09:30:50 +0200	[thread overview]
Message-ID: <20171020073050.nyaqynbbkeltr7iq@gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1710192233130.2054@nanos>


* Thomas Gleixner <tglx@linutronix.de> wrote:

> That would just make the door open for evading lockdep. This has been
> discussed when lockdep was introduced and with a lot of other 'annoying'
> debug features we've seen the same discussion happening.
> 
> When they get introduced the number of real issues and false positives is
> high, but once the dust settles it's just business as usual and the overall
> code quality improves and the number of hard to decode problems shrinks.

Yes, also note that it's typical that the proportion of false positives 
*increases* once a lock debugging feature enters a more mature period of its 
existence, because real deadlocks tend to be fixed at the development stage 
without us ever seeing them.

I.e. for every lockdep-debugged bug fixed upstream I'm pretty sure there are at 
least 10 times as many bugs that were fixed in earlier stages of development, 
without ever hitting the upstream kernel. At least that's the rough proportion
for locking bugs I introduce ;-)

So even false positives are not a problem as long as their annotation improves the 
code or documents it better.

Thanks,

	Ingo

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  reply	other threads:[~2017-10-20  7:30 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-19  5:55 [PATCH v2 0/3] crossrelease: make it not unwind by default Byungchul Park
2017-10-19  5:55 ` Byungchul Park
2017-10-19  5:55 ` [PATCH v2 1/3] lockdep: Introduce CROSSRELEASE_STACK_TRACE and make it not unwind as default Byungchul Park
2017-10-19  5:55   ` Byungchul Park
2017-10-19  5:55 ` [PATCH v2 2/3] lockdep: Remove BROKEN flag of LOCKDEP_CROSSRELEASE Byungchul Park
2017-10-19  5:55   ` Byungchul Park
2017-10-19 15:05   ` Bart Van Assche
2017-10-19 15:05     ` Bart Van Assche
2017-10-19 15:34     ` Thomas Gleixner
2017-10-19 15:34       ` Thomas Gleixner
2017-10-19 15:47       ` Bart Van Assche
2017-10-19 19:04         ` Thomas Gleixner
2017-10-19 19:04           ` Thomas Gleixner
2017-10-19 19:12           ` Thomas Gleixner
2017-10-19 19:12             ` Thomas Gleixner
2017-10-19 20:21             ` Bart Van Assche
2017-10-19 20:21               ` Bart Van Assche
2017-10-19 20:33               ` Matthew Wilcox
2017-10-19 20:33                 ` Matthew Wilcox
2017-10-19 20:41                 ` Bart Van Assche
2017-10-19 20:53                   ` Thomas Gleixner
2017-10-19 20:53                     ` Thomas Gleixner
2017-10-19 20:49               ` Thomas Gleixner
2017-10-19 20:49                 ` Thomas Gleixner
2017-10-20  7:30                 ` Ingo Molnar [this message]
2017-10-20  7:30                   ` Ingo Molnar
2017-10-20  6:03               ` Byungchul Park
2017-10-20  6:03                 ` Byungchul Park
2017-10-19  5:55 ` [PATCH v2 3/3] lockdep: Add a kernel parameter, crossrelease_fullstack Byungchul Park
2017-10-19  5:55   ` Byungchul Park
2017-10-19  7:03 ` [PATCH v2 0/4] Fix false positives by cross-release feature Byungchul Park
2017-10-19  7:03   ` Byungchul Park
2017-10-19  7:03   ` [PATCH v2 1/4] completion: Add support for initializing completion with lockdep_map Byungchul Park
2017-10-19  7:03     ` Byungchul Park
2017-10-19  7:03   ` [PATCH v2 2/4] lockdep: Remove unnecessary acquisitions wrt workqueue flush Byungchul Park
2017-10-19  7:03     ` Byungchul Park
2017-10-19  7:03   ` [PATCH v2 3/4] genhd.h: Remove trailing white space Byungchul Park
2017-10-19  7:03     ` Byungchul Park
2017-10-19  7:03   ` [PATCH v2 4/4] lockdep: Assign a lock_class per gendisk used for wait_for_completion() Byungchul Park
2017-10-19  7:03     ` Byungchul Park
2017-10-20 14:44     ` Christoph Hellwig
2017-10-20 14:44       ` Christoph Hellwig
2017-10-20 14:44       ` Christoph Hellwig
2017-10-22 23:53       ` Byungchul Park
2017-10-22 23:53         ` Byungchul Park
2017-10-23  6:36         ` Christoph Hellwig
2017-10-23  6:36           ` Christoph Hellwig
2017-10-23  7:04           ` Byungchul Park
2017-10-23  7:04             ` Byungchul Park
2017-10-21 19:17     ` kbuild test robot

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20171020073050.nyaqynbbkeltr7iq@gmail.com \
    --to=mingo@kernel.org \
    --cc=Bart.VanAssche@wdc.com \
    --cc=byungchul.park@lge.com \
    --cc=kernel-team@lge.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.