Module Name: src
Committed By: riastradh
Date: Mon Mar 28 12:37:09 UTC 2022
Modified Files:
src/sys/miscfs/specfs: spec_vnops.c specdev.h
Log Message:
specfs: Prevent new opens while close is waiting to drain.
Otherwise, bdev/cdev_close could have cancelled all _existing_ opens,
and waited for them to complete (and freed resources used by them) --
but a new one could start, and hang (e.g., a tty), at the same time
spec_close tries to drain all pending I/O operations, one of which
(the new open) is now hanging indefinitely.
Preventing the new open from even starting until bdev/cdev_close is
finished and all I/O operations have drained avoids this deadlock.
To generate a diff of this commit:
cvs rdiff -u -r1.203 -r1.204 src/sys/miscfs/specfs/spec_vnops.c
cvs rdiff -u -r1.49 -r1.50 src/sys/miscfs/specfs/specdev.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/miscfs/specfs/spec_vnops.c
diff -u src/sys/miscfs/specfs/spec_vnops.c:1.203 src/sys/miscfs/specfs/spec_vnops.c:1.204
--- src/sys/miscfs/specfs/spec_vnops.c:1.203 Mon Mar 28 12:37:01 2022
+++ src/sys/miscfs/specfs/spec_vnops.c Mon Mar 28 12:37:09 2022
@@ -1,4 +1,4 @@
-/* $NetBSD: spec_vnops.c,v 1.203 2022/03/28 12:37:01 riastradh Exp $ */
+/* $NetBSD: spec_vnops.c,v 1.204 2022/03/28 12:37:09 riastradh Exp $ */
/*-
* Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -58,7 +58,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: spec_vnops.c,v 1.203 2022/03/28 12:37:01 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: spec_vnops.c,v 1.204 2022/03/28 12:37:09 riastradh Exp $");
#include <sys/param.h>
#include <sys/proc.h>
@@ -397,6 +397,7 @@ spec_node_init(vnode_t *vp, dev_t rdev)
sd->sd_bdevvp = NULL;
sd->sd_iocnt = 0;
sd->sd_opened = false;
+ sd->sd_closing = false;
sn->sn_dev = sd;
sd = NULL;
} else {
@@ -734,8 +735,17 @@ spec_open(void *v)
case VCHR:
/*
* Character devices can accept opens from multiple
- * vnodes.
+ * vnodes. But first, wait for any close to finish.
+ * Wait under the vnode lock so we don't have to worry
+ * about the vnode being revoked while we wait.
*/
+ while (sd->sd_closing) {
+ error = cv_wait_sig(&specfs_iocv, &device_lock);
+ if (error)
+ break;
+ }
+ if (error)
+ break;
sd->sd_opencnt++;
sn->sn_opencnt++;
break;
@@ -1605,8 +1615,10 @@ spec_close(void *v)
count + 1);
sd->sd_bdevvp = NULL;
}
- if (count == 0)
+ if (count == 0) {
sd->sd_opened = false;
+ sd->sd_closing = true;
+ }
mutex_exit(&device_lock);
if (count != 0)
@@ -1631,6 +1643,18 @@ spec_close(void *v)
*/
spec_io_drain(sd);
+ /*
+ * Wake any spec_open calls waiting for close to finish -- do
+ * this before reacquiring the vnode lock, because spec_open
+ * holds the vnode lock while waiting, so doing this after
+ * reacquiring the lock would deadlock.
+ */
+ mutex_enter(&device_lock);
+ KASSERT(sd->sd_closing);
+ sd->sd_closing = false;
+ cv_broadcast(&specfs_iocv);
+ mutex_exit(&device_lock);
+
if (!(flags & FNONBLOCK))
vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
Index: src/sys/miscfs/specfs/specdev.h
diff -u src/sys/miscfs/specfs/specdev.h:1.49 src/sys/miscfs/specfs/specdev.h:1.50
--- src/sys/miscfs/specfs/specdev.h:1.49 Mon Mar 28 12:36:51 2022
+++ src/sys/miscfs/specfs/specdev.h Mon Mar 28 12:37:09 2022
@@ -1,4 +1,4 @@
-/* $NetBSD: specdev.h,v 1.49 2022/03/28 12:36:51 riastradh Exp $ */
+/* $NetBSD: specdev.h,v 1.50 2022/03/28 12:37:09 riastradh Exp $ */
/*-
* Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -80,6 +80,7 @@ typedef struct specdev {
dev_t sd_rdev;
volatile u_int sd_iocnt; /* # bdev/cdev_* operations active */
bool sd_opened; /* true if successfully opened */
+ bool sd_closing; /* true when bdev/cdev_close ongoing */
} specdev_t;
/*
