git: fad4e7b656b8 - stable/15 - membarrier(2): use atomic for lockless read of curproc->p_flag2

The branch stable/15 has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=fad4e7b656b86befd5995fc4704c68e57a96caa6

commit fad4e7b656b86befd5995fc4704c68e57a96caa6
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2026-04-18 18:42:56 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2026-04-27 01:28:59 +0000

    membarrier(2): use atomic for lockless read of curproc->p_flag2
    
    (cherry picked from commit 950fd59955e10429c1325c327f0141a7e97fcfe5)
---
 sys/kern/kern_membarrier.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/sys/kern/kern_membarrier.c b/sys/kern/kern_membarrier.c
index f0660bd7360e..6d210a1b1783 100644
--- a/sys/kern/kern_membarrier.c
+++ b/sys/kern/kern_membarrier.c
@@ -120,7 +120,7 @@ kern_membarrier(struct thread *td, int cmd, unsigned flags, int cpu_id)
 	struct thread *td1;
 	cpuset_t cs;
 	uint64_t *swt;
-	int c, error;
+	int c, error, f;
 	bool first;
 
 	if (flags != 0 || (cmd & ~MEMBARRIER_SUPPORTED_CMDS) != 0)
@@ -133,6 +133,7 @@ kern_membarrier(struct thread *td, int cmd, unsigned flags, int cpu_id)
 
 	p = td->td_proc;
 	error = 0;
+	f = atomic_load_int(&td->td_proc->p_flag2);
 
 	switch (cmd) {
 	case MEMBARRIER_CMD_GLOBAL:
@@ -155,7 +156,7 @@ kern_membarrier(struct thread *td, int cmd, unsigned flags, int cpu_id)
 		break;
 
 	case MEMBARRIER_CMD_GLOBAL_EXPEDITED:
-		if ((td->td_proc->p_flag2 & P2_MEMBAR_GLOBE) == 0) {
+		if ((f & P2_MEMBAR_GLOBE) == 0) {
 			error = EPERM;
 		} else {
 			CPU_ZERO(&cs);
@@ -171,7 +172,7 @@ kern_membarrier(struct thread *td, int cmd, unsigned flags, int cpu_id)
 		break;
 
 	case MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED:
-		if ((p->p_flag2 & P2_MEMBAR_GLOBE) == 0) {
+		if ((f & P2_MEMBAR_GLOBE) == 0) {
 			PROC_LOCK(p);
 			p->p_flag2 |= P2_MEMBAR_GLOBE;
 			PROC_UNLOCK(p);
@@ -179,7 +180,7 @@ kern_membarrier(struct thread *td, int cmd, unsigned flags, int cpu_id)
 		break;
 
 	case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
-		if ((td->td_proc->p_flag2 & P2_MEMBAR_PRIVE) == 0) {
+		if ((f & P2_MEMBAR_PRIVE) == 0) {
 			error = EPERM;
 		} else {
 			pmap_active_cpus(vmspace_pmap(p->p_vmspace), &cs);
@@ -188,7 +189,7 @@ kern_membarrier(struct thread *td, int cmd, unsigned flags, int cpu_id)
 		break;
 
 	case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED:
-		if ((p->p_flag2 & P2_MEMBAR_PRIVE) == 0) {
+		if ((f & P2_MEMBAR_PRIVE) == 0) {
 			PROC_LOCK(p);
 			p->p_flag2 |= P2_MEMBAR_PRIVE;
 			PROC_UNLOCK(p);
@@ -196,7 +197,7 @@ kern_membarrier(struct thread *td, int cmd, unsigned flags, int cpu_id)
 		break;
 
 	case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
-		if ((td->td_proc->p_flag2 & P2_MEMBAR_PRIVE_SYNCORE) == 0) {
+		if ((f & P2_MEMBAR_PRIVE_SYNCORE) == 0) {
 			error = EPERM;
 		} else {
 			/*