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vfs: lockless writecount adjustment in set/unset text

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... for cases where this is not the first/last exec.
This commit is contained in:
Mateusz Guzik 2021-05-07 16:04:27 +02:00
parent 2cca77ee01
commit b5fb9ae687
1 changed files with 30 additions and 2 deletions
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32
sys/kern/vfs_default.c
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@ -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 (atomic_fcmpset_int(&vp->v_writecount, &n, n - 1)) {
return (0);
}
}
VI_LOCK(vp);
if (vp->v_writecount > 0) {
error = ETXTBSY;
@ -1207,10 +1221,24 @@ static int
vop_stdunset_text(struct vop_unset_text_args *ap)
{
struct vnode *vp;
int error;
int error, n;
bool last;
vp = ap->a_vp;
/*
* Avoid the interlock if this is not the last exec.
*/
n = atomic_load_int(&vp->v_writecount);
for (;;) {
if (n >= -1) {
break;
}
if (atomic_fcmpset_int(&vp->v_writecount, &n, n + 1)) {
return (0);
}
}
last = false;
VI_LOCK(vp);
if (vp->v_writecount < 0) {