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Suspend file system after VFS_MOUNT() and before taking mnt_updating. 

Prevents deadlock against concurrent unmounts of layered file systems.
This commit is contained in:
hannken 2022-07-08 07:43:19 +00:00
parent 42ef1506f1
commit ba6f7f8d2a
1 changed files with 16 additions and 14 deletions
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30
sys/kern/vfs_mount.c
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@ -1,4 +1,4 @@
/* $NetBSD: vfs_mount.c,v 1.93 2022/04/09 23:38:33 riastradh Exp $ */
/* $NetBSD: vfs_mount.c,v 1.94 2022/07/08 07:43:19 hannken Exp $ */
/*-
* Copyright (c) 1997-2020 The NetBSD Foundation, Inc.
@ -67,7 +67,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_mount.c,v 1.93 2022/04/09 23:38:33 riastradh Exp $");
__KERNEL_RCSID(0, "$NetBSD: vfs_mount.c,v 1.94 2022/07/08 07:43:19 hannken Exp $");
#include <sys/param.h>
#include <sys/kernel.h>
@ -773,12 +773,20 @@ mount_domount(struct lwp *l, vnode_t **vpp, struct vfsops *vfsops,
*/
mp->mnt_flag = flags & (MNT_BASIC_FLAGS | MNT_FORCE | MNT_IGNORE);
mutex_enter(mp->mnt_updating);
error = VFS_MOUNT(mp, path, data, data_len);
mp->mnt_flag &= ~MNT_OP_FLAGS;
if (error != 0)
goto err_unmounted;
if (error != 0) {
vfs_rele(mp);
return error;
}
/* Suspend new file system before taking mnt_updating. */
do {
error2 = vfs_suspend(mp, 0);
} while (error2 == EINTR || error2 == ERESTART);
KASSERT(error2 == 0 || error2 == EOPNOTSUPP);
mutex_enter(mp->mnt_updating);
/*
* Validate and prepare the mount point.
@ -823,6 +831,8 @@ mount_domount(struct lwp *l, vnode_t **vpp, struct vfsops *vfsops,
mount_checkdirs(vp);
mutex_exit(mp->mnt_updating);
if (error2 == 0)
vfs_resume(mp);
/* Hold an additional reference to the mount across VFS_START(). */
vfs_ref(mp);
@ -840,19 +850,11 @@ mount_domount(struct lwp *l, vnode_t **vpp, struct vfsops *vfsops,
return error;
err_mounted:
do {
error2 = vfs_suspend(mp, 0);
} while (error2 == EINTR || error2 == ERESTART);
KASSERT(error2 == 0 || error2 == EOPNOTSUPP);
if (VFS_UNMOUNT(mp, MNT_FORCE) != 0)
panic("Unmounting fresh file system failed");
mutex_exit(mp->mnt_updating);
if (error2 == 0)
vfs_resume(mp);
err_unmounted:
mutex_exit(mp->mnt_updating);
vfs_rele(mp);
return error;