* incremented count after it has set MNT_WRITE_HOLD.
*/
smp_mb();
- while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD)
- cpu_relax();
+ might_lock(&mount_lock.lock);
+ while (READ_ONCE(mnt->mnt.mnt_flags) & MNT_WRITE_HOLD) {
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
+ cpu_relax();
+ } else {
+ /*
+ * This prevents priority inversion, if the task
+ * setting MNT_WRITE_HOLD got preempted on a remote
+ * CPU, and it prevents life lock if the task setting
+ * MNT_WRITE_HOLD has a lower priority and is bound to
+ * the same CPU as the task that is spinning here.
+ */
+ preempt_enable();
+ lock_mount_hash();
+ unlock_mount_hash();
+ preempt_disable();
+ }
+ }
/*
* After the slowpath clears MNT_WRITE_HOLD, mnt_is_readonly will
* be set to match its requirements. So we must not load that until
lock_mount_hash();
list_for_each_entry(mnt, &sb->s_mounts, mnt_instance) {
if (!(mnt->mnt.mnt_flags & MNT_READONLY)) {
- mnt->mnt.mnt_flags |= MNT_WRITE_HOLD;
- smp_mb();
- if (mnt_get_writers(mnt) > 0) {
- err = -EBUSY;
+ err = mnt_hold_writers(mnt);
+ if (err)
break;
- }
}
}
if (!err && atomic_long_read(&sb->s_remove_count))
return 0;
}
-static struct mount *mount_setattr_prepare(struct mount_kattr *kattr,
- struct mount *mnt, int *err)
+/**
+ * mnt_allow_writers() - check whether the attribute change allows writers
+ * @kattr: the new mount attributes
+ * @mnt: the mount to which @kattr will be applied
+ *
+ * Check whether thew new mount attributes in @kattr allow concurrent writers.
+ *
+ * Return: true if writers need to be held, false if not
+ */
+static inline bool mnt_allow_writers(const struct mount_kattr *kattr,
+ const struct mount *mnt)
{
- struct mount *m = mnt, *last = NULL;
+ return !(kattr->attr_set & MNT_READONLY) ||
+ (mnt->mnt.mnt_flags & MNT_READONLY);
+}
- if (!is_mounted(&m->mnt)) {
- *err = -EINVAL;
- goto out;
- }
+static int mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt)
+{
+ struct mount *m;
+ int err;
- if (!(mnt_has_parent(m) ? check_mnt(m) : is_anon_ns(m->mnt_ns))) {
- *err = -EINVAL;
- goto out;
- }
+ for (m = mnt; m; m = next_mnt(m, mnt)) {
+ if (!can_change_locked_flags(m, recalc_flags(kattr, m))) {
+ err = -EPERM;
+ break;
+ }
- do {
- unsigned int flags;
+ err = can_idmap_mount(kattr, m);
+ if (err)
+ break;
- flags = recalc_flags(kattr, m);
- if (!can_change_locked_flags(m, flags)) {
- *err = -EPERM;
- goto out;
+ if (!mnt_allow_writers(kattr, m)) {
+ err = mnt_hold_writers(m);
+ if (err)
+ break;
}
- *err = can_idmap_mount(kattr, m);
- if (*err)
- goto out;
+ if (!kattr->recurse)
+ return 0;
+ }
- last = m;
+ if (err) {
+ struct mount *p;
- if ((kattr->attr_set & MNT_READONLY) &&
- !(m->mnt.mnt_flags & MNT_READONLY)) {
- *err = mnt_hold_writers(m);
- if (*err)
- goto out;
+ for (p = mnt; p != m; p = next_mnt(p, mnt)) {
+ /* If we had to hold writers unblock them. */
+ if (p->mnt.mnt_flags & MNT_WRITE_HOLD)
+ mnt_unhold_writers(p);
}
- } while (kattr->recurse && (m = next_mnt(m, mnt)));
-
-out:
- return last;
+ }
+ return err;
}
static void do_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt)
put_user_ns(old_mnt_userns);
}
-static void mount_setattr_commit(struct mount_kattr *kattr,
- struct mount *mnt, struct mount *last,
- int err)
+static void mount_setattr_commit(struct mount_kattr *kattr, struct mount *mnt)
{
- struct mount *m = mnt;
+ struct mount *m;
- do {
- if (!err) {
- unsigned int flags;
+ for (m = mnt; m; m = next_mnt(m, mnt)) {
+ unsigned int flags;
- do_idmap_mount(kattr, m);
- flags = recalc_flags(kattr, m);
- WRITE_ONCE(m->mnt.mnt_flags, flags);
- }
+ do_idmap_mount(kattr, m);
+ flags = recalc_flags(kattr, m);
+ WRITE_ONCE(m->mnt.mnt_flags, flags);
- /*
- * We either set MNT_READONLY above so make it visible
- * before ~MNT_WRITE_HOLD or we failed to recursively
- * apply mount options.
- */
- if ((kattr->attr_set & MNT_READONLY) &&
- (m->mnt.mnt_flags & MNT_WRITE_HOLD))
+ /* If we had to hold writers unblock them. */
+ if (m->mnt.mnt_flags & MNT_WRITE_HOLD)
mnt_unhold_writers(m);
- if (!err && kattr->propagation)
+ if (kattr->propagation)
change_mnt_propagation(m, kattr->propagation);
-
- /*
- * On failure, only cleanup until we found the first mount
- * we failed to handle.
- */
- if (err && m == last)
+ if (!kattr->recurse)
break;
- } while (kattr->recurse && (m = next_mnt(m, mnt)));
-
- if (!err)
- touch_mnt_namespace(mnt->mnt_ns);
+ }
+ touch_mnt_namespace(mnt->mnt_ns);
}
static int do_mount_setattr(struct path *path, struct mount_kattr *kattr)
{
- struct mount *mnt = real_mount(path->mnt), *last = NULL;
+ struct mount *mnt = real_mount(path->mnt);
int err = 0;
if (path->dentry != mnt->mnt.mnt_root)
}
}
+ err = -EINVAL;
lock_mount_hash();
+ /* Ensure that this isn't anything purely vfs internal. */
+ if (!is_mounted(&mnt->mnt))
+ goto out;
+
/*
- * Get the mount tree in a shape where we can change mount
- * properties without failure.
+ * If this is an attached mount make sure it's located in the callers
+ * mount namespace. If it's not don't let the caller interact with it.
+ * If this is a detached mount make sure it has an anonymous mount
+ * namespace attached to it, i.e. we've created it via OPEN_TREE_CLONE.
*/
- last = mount_setattr_prepare(kattr, mnt, &err);
- if (last) /* Commit all changes or revert to the old state. */
- mount_setattr_commit(kattr, mnt, last, err);
+ if (!(mnt_has_parent(mnt) ? check_mnt(mnt) : is_anon_ns(mnt->mnt_ns)))
+ goto out;
+ /*
+ * First, we get the mount tree in a shape where we can change mount
+ * properties without failure. If we succeeded to do so we commit all
+ * changes and if we failed we clean up.
+ */
+ err = mount_setattr_prepare(kattr, mnt);
+ if (!err)
+ mount_setattr_commit(kattr, mnt);
+
+out:
unlock_mount_hash();
if (kattr->propagation) {
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