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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.
This commit is contained in:
riastradh 2022-03-28 12:37:09 +00:00
parent c7aa557804
commit daba8dd87b
2 changed files with 30 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
sys/miscfs/specfs/spec_vnops.c
View File

@ -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);

3
sys/miscfs/specfs/specdev.h
View File

@ -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;
/*