Re: git: fe66e4caf456 - main - rangelock: Disable cheat mode by default

On 27 Aug 2024, at 21:38, Mark Johnston <markj@FreeBSD.org> wrote:
> 
> The branch main has been updated by markj:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=fe66e4caf4561ee3349ad7a29cc9976108c3b04f
> 
> commit fe66e4caf4561ee3349ad7a29cc9976108c3b04f
> Author:     Mark Johnston <markj@FreeBSD.org>
> AuthorDate: 2024-08-27 20:31:25 +0000
> Commit:     Mark Johnston <markj@FreeBSD.org>
> CommitDate: 2024-08-27 20:36:31 +0000
> 
>    rangelock: Disable cheat mode by default
> 
>    Cheat mode is incompatible with code which locks multiple ranges in the
>    same vnode, with at least one range being write-locked.  This can arise
>    in kern_copy_file_range().  Until that's handled somehow, avoid the
>    problem to make the fusefs tests stable.
> 
>    PR:             281073
>    Fixes:          9ef425e560a9 ("rangelocks: add fast cheating mode")
>    Reviewed by:    kib
>    Differential Revision:  https://reviews.freebsd.org/D46457
> ---
> sys/kern/kern_rangelock.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sys/kern/kern_rangelock.c b/sys/kern/kern_rangelock.c
> index 14163dd1c782..38449f71a8b7 100644
> --- a/sys/kern/kern_rangelock.c
> +++ b/sys/kern/kern_rangelock.c
> @@ -66,7 +66,7 @@
>  * trylocks are same as normal locks but do not drain.
>  */
> 
> -static int rangelock_cheat = 1;
> +static int rangelock_cheat = 0;

This probably deserves a comment for why it’s disabled/the risks of
enabling it, and/or some text in the sysctl description?

Jess

> SYSCTL_INT(_debug, OID_AUTO, rangelock_cheat, CTLFLAG_RWTUN,
>     &rangelock_cheat, 0,
>     "");