From c00e3ee5947324bc41b88ad8619d4c3992b60d9b Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Thu, 10 Mar 2022 00:55:42 +0000
Subject: [PATCH 1/2] kern: Use atomic_store_release/atomic_load_consume for
pid_table.
This is read without the lock, so ordering is required.
---
sys/kern/kern_proc.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c
index 90f383ef0fd8..dc5a3d7400fc 100644
--- a/sys/kern/kern_proc.c
+++ b/sys/kern/kern_proc.c
@@ -695,7 +695,7 @@ proc_find_lwp(proc_t *p, pid_t pid)
* memory barrier for dependent loads on alpha.
*/
s = pserialize_read_enter();
- pt = &pid_table[pid & pid_tbl_mask];
+ pt = &atomic_load_consume(&pid_table)[pid & pid_tbl_mask];
slot = atomic_load_consume(&pt->pt_slot);
if (__predict_false(!PT_IS_LWP(slot))) {
pserialize_read_exit(s);
@@ -753,7 +753,7 @@ proc_find_lwp_unlocked(proc_t *p, pid_t pid)
* care to read the slot atomically and only once. This issues a
* memory barrier for dependent loads on alpha.
*/
- pt = &pid_table[pid & pid_tbl_mask];
+ pt = &atomic_load_consume(&pid_table)[pid & pid_tbl_mask];
slot = atomic_load_consume(&pt->pt_slot);
if (__predict_false(!PT_IS_LWP(slot))) {
return NULL;
@@ -1003,7 +1003,7 @@ expand_pid_table(void)
/* Save old table size and switch tables */
tsz = pt_size * sizeof(struct pid_table);
n_pt = pid_table;
- pid_table = new_pt;
+ atomic_store_release(&pid_table, new_pt);
pid_tbl_mask = new_pt_mask;
/*
From 0975b0fcc8a998909ef7b89e1119a7ddbd742a9e Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Thu, 10 Mar 2022 00:57:02 +0000
Subject: [PATCH 2/2] kern: Use atomic_store_release for pid_table::pt_slot.
Not clear the necessary membar was issued in proc_alloc_pid. Fewer
store-release once at boot, not a big deal.
---
sys/kern/kern_proc.c | 15 +++------------
1 file changed, 3 insertions(+), 12 deletions(-)
diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c
index dc5a3d7400fc..fdbb3338cff8 100644
--- a/sys/kern/kern_proc.c
+++ b/sys/kern/kern_proc.c
@@ -1083,7 +1083,7 @@ proc_alloc_pid_slot(struct proc *p, uintptr_t slot)
p != &proc0)) {
KASSERT(PT_IS_PROC(slot));
pt = &pid_table[1];
- pt->pt_slot = slot;
+ atomic_store_release(&pt->pt_slot, slot);
return 1;
}
pt = &pid_table[next_free_pt];
@@ -1107,7 +1107,7 @@ proc_alloc_pid_slot(struct proc *p, uintptr_t slot)
KASSERT(pid <= FUTEX_TID_MASK);
/* Grab table slot */
- pt->pt_slot = slot;
+ atomic_store_release(&pt->pt_slot, slot);
KASSERT(pt->pt_pid == 0);
pt->pt_pid = pid;
@@ -1143,15 +1143,6 @@ proc_alloc_lwpid(struct proc *p, struct lwp *l)
KASSERT(l->l_proc == p);
KASSERT(l->l_stat == LSIDL);
- /*
- * For unlocked lookup in proc_find_lwp(), make sure l->l_proc
- * is globally visible before the LWP becomes visible via the
- * pid_table.
- */
-#ifndef __HAVE_ATOMIC_AS_MEMBAR
- membar_producer();
-#endif
-
/*
* If the slot for p->p_pid currently points to the proc,
* then we should usurp this ID for the LWP. This happens
@@ -1166,7 +1157,7 @@ proc_alloc_lwpid(struct proc *p, struct lwp *l)
if (PT_IS_PROC(pt->pt_slot)) {
KASSERT(PT_GET_PROC(pt->pt_slot) == p);
l->l_lid = pid;
- pt->pt_slot = PT_SET_LWP(l);
+ atomic_store_release(&pt->pt_slot, PT_SET_LWP(l));
} else {
/* Need to allocate a new slot. */
pid = proc_alloc_pid_slot(p, PT_SET_LWP(l));