From 4d570ec9542763021c3e3d22a7aebd6842932c45 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Thu, 24 Feb 2022 15:53:11 +0000
Subject: [PATCH 16/49] WIP: kern_descrip.c: Membar audit.
---
sys/kern/kern_descrip.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index 1336ea9b8010..a1fa3bcdbdeb 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -392,6 +392,9 @@ fd_getfile(unsigned fd)
* Multi threaded: issue a memory barrier to ensure that we
* acquire the file pointer _after_ adding a reference. If
* no memory barrier, we could fetch a stale pointer.
+ *
+ * XXX Unclear what stale pointer this refers to... I
+ * don't think this membar is actually necessary.
*/
atomic_inc_uint(&ff->ff_refcnt);
#ifndef __HAVE_ATOMIC_AS_MEMBAR
@@ -451,7 +454,7 @@ fd_putfile(unsigned fd)
* CPU.
*/
#ifndef __HAVE_ATOMIC_AS_MEMBAR
- membar_exit();
+ membar_release();
#endif
/*
@@ -602,6 +605,9 @@ fd_close(unsigned fd)
* waiting for other users of the file to drain. Release
* our reference, and wake up the closer.
*/
+#ifndef __HAVE_ATOMIC_AS_MEMBAR
+ membar_release();
+#endif
atomic_dec_uint(&ff->ff_refcnt);
cv_broadcast(&ff->ff_closing);
mutex_exit(&fdp->fd_lock);
@@ -637,7 +643,7 @@ fd_close(unsigned fd)
} else {
/* Multi threaded. */
#ifndef __HAVE_ATOMIC_AS_MEMBAR
- membar_producer();
+ membar_release();
#endif
refcnt = atomic_dec_uint_nv(&ff->ff_refcnt);
}
@@ -683,7 +689,13 @@ fd_close(unsigned fd)
cv_wait(&ff->ff_closing, &fdp->fd_lock);
}
atomic_and_uint(&ff->ff_refcnt, ~FR_CLOSING);
+#ifndef __HAVE_ATOMIC_AS_MEMBAR
+ membar_acquire();
+#endif
} else {
+#ifndef __HAVE_ATOMIC_AS_MEMBAR
+ membar_acquire();
+#endif
/* If no references, there must be no knotes. */
KASSERT(SLIST_EMPTY(&ff->ff_knlist));
}
@@ -1532,10 +1544,13 @@ fd_free(void)
KASSERT(fdp->fd_dtbuiltin.dt_link == NULL);
#ifndef __HAVE_ATOMIC_AS_MEMBAR
- membar_exit();
+ membar_release();
#endif
if (atomic_dec_uint_nv(&fdp->fd_refcnt) > 0)
return;
+#ifndef __HAVE_ATOMIC_AS_MEMBAR
+ membar_acquire();
+#endif
/*
* Close any files that the process holds open.
--
2.33.0