Re: CVS commit: src/sys/kern

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

On 2025/04/09 14:38, Rin Okuyama wrote:
> Module Name:	src
> Committed By:	rin
> Date:		Wed Apr  9 05:38:01 UTC 2025
>
> Modified Files:
> 	src/sys/kern: subr_log.c
>
> Log Message:
> logread: Stop reading msgbuf without log_lock being held

Oops, sorry, here I made typo; s/reading/writing/

Thanks,
rin

> Idea taken from FreeBSD.
>
> XXX
> The size of temporal buffer on stack (== 128) is also taken from FreeBSD.
> We are not very sure whether this value is optimal or not. But we don't
> expect performance regression from this choice.
>
> No new regression for full ATF run on amd64 with DIAGNOSTIC+LOCKDEBUG
> kernel and rump kernel.
>
> Authored by knakahara@.
>
>
> To generate a diff of this commit:
> cvs rdiff -u -r1.65 -r1.66 src/sys/kern/subr_log.c
>
> Please note that diffs are not public domain; they are subject to the
> copyright notices on the relevant files.
>
>
> Modified files:
>
> Index: src/sys/kern/subr_log.c
> diff -u src/sys/kern/subr_log.c:1.65 src/sys/kern/subr_log.c:1.66
> --- src/sys/kern/subr_log.c:1.65	Tue Apr  8 04:19:28 2025
> +++ src/sys/kern/subr_log.c	Wed Apr  9 05:38:01 2025
> @@ -1,4 +1,4 @@
> -/*	$NetBSD: subr_log.c,v 1.65 2025/04/08 04:19:28 rin Exp $	*/
> +/*	$NetBSD: subr_log.c,v 1.66 2025/04/09 05:38:01 rin Exp $	*/
>   
>   /*-
>    * Copyright (c) 2007, 2008 The NetBSD Foundation, Inc.
> @@ -65,7 +65,7 @@
>    */
>   
>   #include <sys/cdefs.h>
> -__KERNEL_RCSID(0, "$NetBSD: subr_log.c,v 1.65 2025/04/08 04:19:28 rin Exp $");
> +__KERNEL_RCSID(0, "$NetBSD: subr_log.c,v 1.66 2025/04/09 05:38:01 rin Exp $");
>   
>   #include <sys/param.h>
>   #include <sys/systm.h>
> @@ -219,20 +219,25 @@ logread(dev_t dev, struct uio *uio, int
>   		}
>   	}
>   	while (uio->uio_resid > 0) {
> +		char buf[128]; /* taken from FreeBSD */
> +
>   		l = mbp->msg_bufx - mbp->msg_bufr;
>   		if (l < 0)
>   			l = mbp->msg_bufs - mbp->msg_bufr;
>   		l = ulmin(l, uio->uio_resid);
>   		if (l == 0)
>   			break;
> +
> +		l = ulmin(l, sizeof(buf));
> +		memcpy(buf, &mbp->msg_bufc[mbp->msg_bufr], l);
> +		mbp->msg_bufr += l;
> +		if (mbp->msg_bufr < 0 || mbp->msg_bufr >= mbp->msg_bufs)
> +			mbp->msg_bufr = 0;
>   		mutex_spin_exit(&log_lock);
> -		error = uiomove(&mbp->msg_bufc[mbp->msg_bufr], l, uio);
> +		error = uiomove(buf, l, uio);
>   		mutex_spin_enter(&log_lock);
>   		if (error)
>   			break;
> -		mbp->msg_bufr += l;
> -		if (mbp->msg_bufr < 0 || mbp->msg_bufr >= mbp->msg_bufs)
> -			mbp->msg_bufr = 0;
>   	}
>   	mutex_spin_exit(&log_lock);
>