The branch main has been updated by mjg:
URL:
https://cgit.FreeBSD.org/src/commit/?id=b5fb9ae6872c499f1a02bec41f48b163a73a2aaa
commit b5fb9ae6872c499f1a02bec41f48b163a73a2aaa
Author: Mateusz Guzik <m...@freebsd.org>
AuthorDate: 2021-05-07 14:04:27 +0000
Commit: Mateusz Guzik <m...@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 (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) {
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