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zfs_get_vfs: reference a requested filesystem instead of vfs_busy-ing it

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The only consumer of zfs_get_vfs, zfs_unmount_snap, does not need
the filesystem to be busy, it just need a reference that it can pass
to dounmount.

Also, previously the code was racy as it unbusied the filesystem
before taking a reference on it.

Now the code should be simpler and safer.

MFC after:	2 weeks
Sponsored by:	Panzura
This commit is contained in:
Andriy Gapon 2017-09-12 06:04:01 +00:00
parent f7519dbb76
commit d092f79489
1 changed files with 6 additions and 10 deletions
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16
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c
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@ -3049,13 +3049,11 @@ zfs_get_vfs(const char *resource)
mtx_lock(&mountlist_mtx);
TAILQ_FOREACH(vfsp, &mountlist, mnt_list) {
if (strcmp(refstr_value(vfsp->vfs_resource), resource) == 0) {
if (vfs_busy(vfsp, MBF_MNTLSTLOCK) != 0)
vfsp = NULL;
vfs_ref(vfsp);
break;
}
}
if (vfsp == NULL)
mtx_unlock(&mountlist_mtx);
mtx_unlock(&mountlist_mtx);
return (vfsp);
}
@ -3545,7 +3543,9 @@ zfs_unmount_snap(const char *snapname)
{
vfs_t *vfsp;
zfsvfs_t *zfsvfs;
#ifdef illumos
int err;
#endif
if (strchr(snapname, '@') == NULL)
return (0);
@ -3557,23 +3557,19 @@ zfs_unmount_snap(const char *snapname)
zfsvfs = vfsp->vfs_data;
ASSERT(!dsl_pool_config_held(dmu_objset_pool(zfsvfs->z_os)));
err = vn_vfswlock(vfsp->vfs_vnodecovered);
#ifdef illumos
err = vn_vfswlock(vfsp->vfs_vnodecovered);
VFS_RELE(vfsp);
#else
vfs_unbusy(vfsp);
#endif
if (err != 0)
return (SET_ERROR(err));
#endif
/*
* Always force the unmount for snapshots.
*/
#ifdef illumos
(void) dounmount(vfsp, MS_FORCE, kcred);
#else
vfs_ref(vfsp);
(void) dounmount(vfsp, MS_FORCE, curthread);
#endif
return (0);