linux-kernel - Re: LOCKDEP customizable numbers upper limit

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Message-ID: <f323397b-dbe7-b655-4624-d243c2f68d81@i-love.sakura.ne.jp>
Date:   Thu, 13 May 2021 23:27:53 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     "J. R. Okajima" <hooanon05g@...il.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org
Subject: Re: LOCKDEP customizable numbers upper limit

On 2021/05/13 22:39, J. R. Okajima wrote:
> Hello,
> 
> According to the commit in v5.13-rc1,
> 	5dc33592e9553 2021-04-05 lockdep: Allow tuning tracing capacity constants.
> several lockdep numbers have their own range as 10--30.
> But if we set all 30s, we got a compilation error.

Thanks for your report.

Initial proposal at
https://lore.kernel.org/lkml/1595640639-9310-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp/
allowed only "double the upper limits", and subsequent proposals allowed arbitrary sizes in
response to https://lore.kernel.org/lkml/CACT4Y+YXT9iLij-AbrUwj=yPq-YNFw=Au9g0LQJCKwYonaHCDQ@mail.gmail.com/ ,
but practically increasing by a few bits should be sufficient.

I'm never expecting to use 30. I'm sure that setting 30s will become a too
much memory consumer that will prevent the kernel from booting correctly.
Thus, I don't think we need to care about randconfig kernels.

Please submit a patch that avoids only BUILD_BUG_ON().

Regards.