git: b5fb9ae6872c - main - vfs: lockless writecount adjustment in set/unset text

[Konstantin Belousov]

On Fri, May 14, 2021 at 02:23:55PM +0000, Mateusz Guzik wrote:
> The branch main has been updated by mjg:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=b5fb9ae6872c499f1a02bec41f48b163a73a2aaa
> 
> commit b5fb9ae6872c499f1a02bec41f48b163a73a2aaa
> Author:     Mateusz Guzik <mjg at FreeBSD.org>
> AuthorDate: 2021-05-07 14:04:27 +0000
> Commit:     Mateusz Guzik <mjg at FreeBSD.org>
> CommitDate: 2021-05-14 14:22:21 +0000
> 
>     vfs: lockless writecount adjustment in set/unset text
>     
>     ... for cases where this is not the first/last exec.
> ---
>  sys/kern/vfs_default.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/sys/kern/vfs_default.c b/sys/kern/vfs_default.c
> index cf224981cbe7..3518bbeaa279 100644
> --- a/sys/kern/vfs_default.c
> +++ b/sys/kern/vfs_default.c
> @@ -1177,9 +1177,23 @@ vop_stdset_text(struct vop_set_text_args *ap)
>  {
>  	struct vnode *vp;
>  	struct mount *mp;
> -	int error;
> +	int error, n;
>  
>  	vp = ap->a_vp;
> +
> +	/*
> +	 * Avoid the interlock if execs are already present.
> +	 */
> +	n = atomic_load_int(&vp->v_writecount);
> +	for (;;) {
> +		if (n > -1) {
> +			break;
If you split the VOP for tmpfs/non-tmpfs implementations, then
non-tmpfs can go with the atomics only.