linux-kernel - Re: [PATCH 1/3] lockdep: fix upper limit for LOCKDEP_*

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Message-ID: <0299406c-b316-4e79-848d-b6641dda0031@redhat.com>
Date: Mon, 5 Aug 2024 21:29:45 -0400
From: Waiman Long <longman@...hat.com>
To: Carlos Llamas <cmllamas@...gle.com>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, kernel-team@...roid.com,
 "J. R. Okajima" <hooanon05g@...il.com>, Peter Zijlstra
 <peterz@...radead.org>, Boqun Feng <boqun.feng@...il.com>,
 Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/3] lockdep: fix upper limit for LOCKDEP_*_BITS configs


On 8/5/24 21:01, Carlos Llamas wrote:
> Lockdep has a set of configs used to determine the size of the static
> arrays that it uses. However, the upper limit that was initially setup
> for these configs is too high (30 bit shift). This equates to several
> GiB of static memory for individual symbols. Using such high values
> leads to linker errors:
>
>    $ make defconfig
>    $ ./scripts/config -e PROVE_LOCKING --set-val LOCKDEP_BITS 30
>    $ make olddefconfig all
>    [...]
>    ld: kernel image bigger than KERNEL_IMAGE_SIZE
>    ld: section .bss VMA wraps around address space
>
> Adjust the upper limits to the maximum values that avoid these issues.
> The need for anything more, likely points to a problem elsewhere. Note
> that LOCKDEP_CHAINS_BITS was intentionally left out as its upper limit
> had a different symptom and has already been fixed [1].
>
> Reported-by: J. R. Okajima <hooanon05g@...il.com>
> Closes: https://lore.kernel.org/all/30795.1620913191@jrobl/ [1]
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
> ---
>   lib/Kconfig.debug | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index a81d452941ce..baaaedfde0cb 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1507,7 +1507,7 @@ config LOCKDEP_SMALL
>   config LOCKDEP_BITS
>   	int "Bitsize for MAX_LOCKDEP_ENTRIES"
>   	depends on LOCKDEP && !LOCKDEP_SMALL
> -	range 10 30
> +	range 10 24
>   	default 15
>   	help
>   	  Try increasing this value if you hit "BUG: MAX_LOCKDEP_ENTRIES too low!" message.
> @@ -1523,7 +1523,7 @@ config LOCKDEP_CHAINS_BITS
>   config LOCKDEP_STACK_TRACE_BITS
>   	int "Bitsize for MAX_STACK_TRACE_ENTRIES"
>   	depends on LOCKDEP && !LOCKDEP_SMALL
> -	range 10 30
> +	range 10 26
>   	default 19
>   	help
>   	  Try increasing this value if you hit "BUG: MAX_STACK_TRACE_ENTRIES too low!" message.
> @@ -1531,7 +1531,7 @@ config LOCKDEP_STACK_TRACE_BITS
>   config LOCKDEP_STACK_TRACE_HASH_BITS
>   	int "Bitsize for STACK_TRACE_HASH_SIZE"
>   	depends on LOCKDEP && !LOCKDEP_SMALL
> -	range 10 30
> +	range 10 26
>   	default 14
>   	help
>   	  Try increasing this value if you need large STACK_TRACE_HASH_SIZE.
> @@ -1539,7 +1539,7 @@ config LOCKDEP_STACK_TRACE_HASH_BITS
>   config LOCKDEP_CIRCULAR_QUEUE_BITS
>   	int "Bitsize for elements in circular_queue struct"
>   	depends on LOCKDEP
> -	range 10 30
> +	range 10 26
>   	default 12
>   	help
>   	  Try increasing this value if you hit "lockdep bfs error:-1" warning due to __cq_enqueue() failure.

I agree that we should further limit the max values.

Acked-by: Waiman Long <longman@...hat.com>