From patchwork Mon Jun 17 20:53:14 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christian Hopps X-Patchwork-Id: 13701424 X-Patchwork-Delegate: kuba@kernel.org Received: from smtp.chopps.org (smtp.chopps.org [54.88.81.56]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 13435199E9C for ; Mon, 17 Jun 2024 20:54:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=54.88.81.56 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718657667; cv=none; b=I9vOL4gN1tOvwNB+nUSHhBntxkIQtPXLP7LabKvON+aMUstuTBYrWr7w/91qAtvEL80Q5A+r+c5Voq1h72j2OLnVhJ07AX9YOl+CAWX9rq0ufAU+HZIrNTNbhXtFn6h0z9wvkqRpXgupvrorWzB5Kx0+bFsmvdaIB2onC6YFqi8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1718657667; c=relaxed/simple; bh=T0cdVmvBgKWA7QSjiZurPaqXIMPMgkOA1lYD8JZ3LIY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oc9aMqkvGSZBUv4fOWoOKDt7AtrahcoZ7/D1d8E5dqeLvVGUL3Z2bQ6pfbwm5wCuGmmJqYh6zIHqzGAxl36i1x89smG6+FCNpOKfr1QyHV2lMblfKwVf5fEsYMip/+ICYjxsYp3JLjgnXv+/Q9BCo2d/Bmzt3HTdwHurz+4V544= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=chopps.org; spf=fail smtp.mailfrom=chopps.org; arc=none smtp.client-ip=54.88.81.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=chopps.org Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=chopps.org Received: from labnh.big (syn-172-222-091-149.res.spectrum.com [172.222.91.149]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by smtp.chopps.org (Postfix) with ESMTPSA id A46BF7D127; Mon, 17 Jun 2024 20:54:24 +0000 (UTC) From: Christian Hopps To: devel@linux-ipsec.org Cc: Steffen Klassert , netdev@vger.kernel.org, Christian Hopps , Christian Hopps Subject: [PATCH ipsec-next v4 16/18] xfrm: iptfs: handle reordering of received packets Date: Mon, 17 Jun 2024 16:53:14 -0400 Message-ID: <20240617205316.939774-17-chopps@chopps.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240617205316.939774-1-chopps@chopps.org> References: <20240617205316.939774-1-chopps@chopps.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: kuba@kernel.org From: Christian Hopps Handle the receipt of the outer tunnel packets out-of-order. Pointers to the out-of-order packets are saved in a window (array) awaiting needed prior packets. When the required prior packets are received the now in-order packets are then passed on to the regular packet receive code. A timer is used to consider missing earlier packet as lost so the algorithm will advance. Signed-off-by: Christian Hopps --- net/xfrm/xfrm_iptfs.c | 481 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 469 insertions(+), 12 deletions(-) diff --git a/net/xfrm/xfrm_iptfs.c b/net/xfrm/xfrm_iptfs.c index d54ac197199f..59fd8ee49cd4 100644 --- a/net/xfrm/xfrm_iptfs.c +++ b/net/xfrm/xfrm_iptfs.c @@ -38,8 +38,14 @@ #define IPTFS_HRTIMER_MODE HRTIMER_MODE_REL_SOFT +struct skb_wseq { + struct sk_buff *skb; + u64 drop_time; +}; + struct xfrm_iptfs_config { bool dont_frag : 1; + u16 reorder_win_size; u32 pkt_size; /* outer_packet_size or 0 */ u32 max_queue_size; /* octets */ }; @@ -57,12 +63,16 @@ struct xfrm_iptfs_data { time64_t iptfs_settime; /* time timer was set */ u32 payload_mtu; /* max payload size */ - /* Tunnel egress */ + /* Tunnel input reordering */ + bool w_seq_set; /* true after first seq received */ + u64 w_wantseq; /* expected next sequence */ + struct skb_wseq *w_saved; /* the saved buf array */ + u32 w_savedlen; /* the saved len (not size) */ spinlock_t drop_lock; struct hrtimer drop_timer; u64 drop_time_ns; - /* Tunnel egress reassembly */ + /* Tunnel input reassembly */ struct sk_buff *ra_newskb; /* new pkt being reassembled */ u64 ra_wantseq; /* expected next sequence */ u8 ra_runt[6]; /* last pkt bytes from last skb */ @@ -834,13 +844,13 @@ static u32 iptfs_reassem_cont(struct xfrm_iptfs_data *xtfs, u64 seq, } /** - * iptfs_input() - handle receipt of iptfs payload + * iptfs_input_ordered() - handle next in order IPTFS payload. * @x: xfrm state - * @skb: the packet + * @skb: current packet * * Process the IPTFS payload in `skb` and consume it afterwards. */ -static int iptfs_input(struct xfrm_state *x, struct sk_buff *skb) +static int iptfs_input_ordered(struct xfrm_state *x, struct sk_buff *skb) { u8 hbytes[sizeof(struct ipv6hdr)]; struct ip_iptfs_cc_hdr iptcch; @@ -1163,11 +1173,369 @@ static int iptfs_input(struct xfrm_state *x, struct sk_buff *skb) kfree_skb(skb); } - /* We always have dealt with the input SKB, either we are re-using it, - * or we have freed it. Return EINPROGRESS so that xfrm_input stops - * processing it. + return 0; +} + +/* ------------------------------- */ +/* Input (Egress) Re-ordering Code */ +/* ------------------------------- */ + +static void __vec_shift(struct xfrm_iptfs_data *xtfs, u32 shift) +{ + u32 savedlen = xtfs->w_savedlen; + + if (shift > savedlen) + shift = savedlen; + if (shift != savedlen) + memcpy(xtfs->w_saved, xtfs->w_saved + shift, + (savedlen - shift) * sizeof(*xtfs->w_saved)); + memset(xtfs->w_saved + savedlen - shift, 0, + shift * sizeof(*xtfs->w_saved)); + xtfs->w_savedlen -= shift; +} + +static void __reorder_past(struct xfrm_iptfs_data *xtfs, struct sk_buff *inskb, + struct list_head *freelist) +{ + list_add_tail(&inskb->list, freelist); +} + +static u32 __reorder_drop(struct xfrm_iptfs_data *xtfs, struct list_head *list) + +{ + struct skb_wseq *s, *se; + const u32 savedlen = xtfs->w_savedlen; + time64_t now = ktime_get_raw_fast_ns(); + u32 count = 0; + u32 scount = 0; + + BUG_ON(!savedlen); + if (xtfs->w_saved[0].drop_time > now) + goto set_timer; + + ++xtfs->w_wantseq; + + /* Keep flushing packets until we reach a drop time greater than now. */ + s = xtfs->w_saved; + se = s + savedlen; + do { + /* Walking past empty slots until we reach a packet */ + for (; s < se && !s->skb; s++) + if (s->drop_time > now) + goto outerdone; + /* Sending packets until we hit another empty slot. */ + for (; s < se && s->skb; scount++, s++) + list_add_tail(&s->skb->list, list); + } while (s < se); +outerdone: + + count = s - xtfs->w_saved; + if (count) { + xtfs->w_wantseq += count; + + /* Shift handled slots plus final empty slot into slot 0. */ + __vec_shift(xtfs, count); + } + + if (xtfs->w_savedlen) { +set_timer: + /* Drifting is OK */ + hrtimer_start(&xtfs->drop_timer, + xtfs->w_saved[0].drop_time - now, + IPTFS_HRTIMER_MODE); + } + return scount; +} + +static void __reorder_this(struct xfrm_iptfs_data *xtfs, struct sk_buff *inskb, + struct list_head *list) +{ + struct skb_wseq *s, *se; + const u32 savedlen = xtfs->w_savedlen; + u32 count = 0; + + /* Got what we wanted. */ + list_add_tail(&inskb->list, list); + ++xtfs->w_wantseq; + if (!savedlen) + return; + + /* Flush remaining consecutive packets. */ + + /* Keep sending until we hit another missed pkt. */ + for (s = xtfs->w_saved, se = s + savedlen; s < se && s->skb; s++) + list_add_tail(&s->skb->list, list); + count = s - xtfs->w_saved; + if (count) + xtfs->w_wantseq += count; + + /* Shift handled slots plus final empty slot into slot 0. */ + __vec_shift(xtfs, count + 1); +} + +/* Set the slot's drop time and all the empty slots below it until reaching a + * filled slot which will already be set. + */ +static void iptfs_set_window_drop_times(struct xfrm_iptfs_data *xtfs, int index) +{ + const u32 savedlen = xtfs->w_savedlen; + struct skb_wseq *s = xtfs->w_saved; + time64_t drop_time; + + assert_spin_locked(&xtfs->drop_lock); + + if (savedlen > index + 1) { + /* we are below another, our drop time and the timer are already set */ + BUG_ON(xtfs->w_saved[index + 1].drop_time != + xtfs->w_saved[index].drop_time); + return; + } + /* we are the most future so get a new drop time. */ + drop_time = ktime_get_raw_fast_ns(); + drop_time += xtfs->drop_time_ns; + + /* Walk back through the array setting drop times as we go */ + s[index].drop_time = drop_time; + while (index-- > 0 && !s[index].skb) + s[index].drop_time = drop_time; + + /* If we walked all the way back, schedule the drop timer if needed */ + if (index == -1 && !hrtimer_is_queued(&xtfs->drop_timer)) + hrtimer_start(&xtfs->drop_timer, xtfs->drop_time_ns, + IPTFS_HRTIMER_MODE); +} + +static void __reorder_future_fits(struct xfrm_iptfs_data *xtfs, + struct sk_buff *inskb, + struct list_head *freelist) +{ + const u32 nslots = xtfs->cfg.reorder_win_size + 1; + const u64 inseq = __esp_seq(inskb); + const u64 wantseq = xtfs->w_wantseq; + const u64 distance = inseq - wantseq; + const u32 savedlen = xtfs->w_savedlen; + const u32 index = distance - 1; + + BUG_ON(distance >= nslots); + + /* Handle future sequence number received which fits in the window. + * + * We know we don't have the seq we want so we won't be able to flush + * anything. */ - return -EINPROGRESS; + + /* slot count is 4, saved size is 3 savedlen is 2 + * + * "window boundary" is based on the fixed window size + * distance is also slot number + * index is an array index (i.e., - 1 of slot) + * : : - implicit NULL after array len + * + * +--------- used length (savedlen == 2) + * | +----- array size (nslots - 1 == 3) + * | | + window boundary (nslots == 4) + * V V | V + * | + * 0 1 2 3 | slot number + * --- 0 1 2 | array index + * [-] [b] : :| array + * + * "2" "3" "4" *5*| seq numbers + * + * We receive seq number 5 + * distance == 3 [inseq(5) - w_wantseq(2)] + * index == 2 [distance(6) - 1] + */ + + if (xtfs->w_saved[index].skb) { + /* a dup of a future */ + list_add_tail(&inskb->list, freelist); + return; + } + + xtfs->w_saved[index].skb = inskb; + xtfs->w_savedlen = max(savedlen, index + 1); + iptfs_set_window_drop_times(xtfs, index); +} + +static void __reorder_future_shifts(struct xfrm_iptfs_data *xtfs, + struct sk_buff *inskb, + struct list_head *list, + struct list_head *freelist) +{ + const u32 nslots = xtfs->cfg.reorder_win_size + 1; + const u64 inseq = __esp_seq(inskb); + u32 savedlen = xtfs->w_savedlen; + u64 wantseq = xtfs->w_wantseq; + struct sk_buff *slot0 = NULL; + struct skb_wseq *wnext; + u32 beyond, shifting, slot; + u64 distance; + + BUG_ON(inseq <= wantseq); + distance = inseq - wantseq; + BUG_ON(distance <= nslots - 1); + beyond = distance - (nslots - 1); + + /* Handle future sequence number received. + * + * IMPORTANT: we are at least advancing w_wantseq (i.e., wantseq) by 1 + * b/c we are beyond the window boundary. + * + * We know we don't have the wantseq so that counts as a drop. + */ + + /* ex: slot count is 4, array size is 3 savedlen is 2, slot 0 is the + * missing sequence number. + * + * the final slot at savedlen (index savedlen - 1) is always occupied. + * + * beyond is "beyond array size" not savedlen. + * + * +--------- array length (savedlen == 2) + * | +----- array size (nslots - 1 == 3) + * | | +- window boundary (nslots == 4) + * V V | V + * | + * 0 1 2 3 | slot number + * --- 0 1 2 | array index + * [b] [c] : :| array + * | + * "2" "3" "4" "5"|*6* seq numbers + * + * We receive seq number 6 + * distance == 4 [inseq(6) - w_wantseq(2)] + * newslot == distance + * index == 3 [distance(4) - 1] + * beyond == 1 [newslot(4) - lastslot((nslots(4) - 1))] + * shifting == 1 [min(savedlen(2), beyond(1)] + * slot0_skb == [b], and should match w_wantseq + * + * +--- window boundary (nslots == 4) + * 0 1 2 3 | 4 slot number + * --- 0 1 2 | 3 array index + * [b] : : : :| array + * "2" "3" "4" "5" *6* seq numbers + * + * We receive seq number 6 + * distance == 4 [inseq(6) - w_wantseq(2)] + * newslot == distance + * index == 3 [distance(4) - 1] + * beyond == 1 [newslot(4) - lastslot((nslots(4) - 1))] + * shifting == 1 [min(savedlen(1), beyond(1)] + * slot0_skb == [b] and should match w_wantseq + * + * +-- window boundary (nslots == 4) + * 0 1 2 3 | 4 5 6 slot number + * --- 0 1 2 | 3 4 5 array index + * [-] [c] : :| array + * "2" "3" "4" "5" "6" "7" *8* seq numbers + * + * savedlen = 2, beyond = 3 + * iter 1: slot0 == NULL, missed++, lastdrop = 2 (2+1-1), slot0 = [-] + * iter 2: slot0 == NULL, missed++, lastdrop = 3 (2+2-1), slot0 = [c] + * 2 < 3, extra = 1 (3-2), missed += extra, lastdrop = 4 (2+2+1-1) + * + * We receive seq number 8 + * distance == 6 [inseq(8) - w_wantseq(2)] + * newslot == distance + * index == 5 [distance(6) - 1] + * beyond == 3 [newslot(6) - lastslot((nslots(4) - 1))] + * shifting == 2 [min(savedlen(2), beyond(3)] + * + * slot0_skb == NULL changed from [b] when "savedlen < beyond" is true. + */ + + /* Now send any packets that are being shifted out of saved, and account + * for missing packets that are exiting the window as we shift it. + */ + + /* If savedlen > beyond we are shifting some, else all. */ + shifting = min(savedlen, beyond); + + /* slot0 is the buf that just shifted out and into slot0 */ + slot0 = NULL; + wnext = xtfs->w_saved; + for (slot = 1; slot <= shifting; slot++, wnext++) { + /* handle what was in slot0 before we occupy it */ + if (slot0) + list_add_tail(&slot0->list, list); + slot0 = wnext->skb; + wnext->skb = NULL; + } + + /* slot0 is now either NULL (in which case it's what we now are waiting + * for, or a buf in which case we need to handle it like we received it; + * however, we may be advancing past that buffer as well.. + */ + + /* Handle case where we need to shift more than we had saved, slot0 will + * be NULL iff savedlen is 0, otherwise slot0 will always be + * non-NULL b/c we shifted the final element, which is always set if + * there is any saved, into slot0. + */ + if (savedlen < beyond) { + if (savedlen == 0) { + BUG_ON(slot0); + } else { + BUG_ON(!slot0); + list_add_tail(&slot0->list, list); + } + slot0 = NULL; + /* slot0 has had an empty slot pushed into it */ + } + + /* Remove the entries */ + __vec_shift(xtfs, beyond); + + /* Advance want seq */ + xtfs->w_wantseq += beyond; + + /* Process drops here when implementing congestion control */ + + /* We've shifted. plug the packet in at the end. */ + xtfs->w_savedlen = nslots - 1; + xtfs->w_saved[xtfs->w_savedlen - 1].skb = inskb; + iptfs_set_window_drop_times(xtfs, xtfs->w_savedlen - 1); + + /* if we don't have a slot0 then we must wait for it */ + if (!slot0) + return; + + /* If slot0, seq must match new want seq */ + BUG_ON(xtfs->w_wantseq != __esp_seq(slot0)); + + /* slot0 is valid, treat like we received expected. */ + __reorder_this(xtfs, slot0, list); +} + +/* Receive a new packet into the reorder window. Return a list of ordered + * packets from the window. + */ +static void iptfs_input_reorder(struct xfrm_iptfs_data *xtfs, + struct sk_buff *inskb, struct list_head *list, + struct list_head *freelist) +{ + const u32 nslots = xtfs->cfg.reorder_win_size + 1; + u64 inseq = __esp_seq(inskb); + u64 wantseq; + + assert_spin_locked(&xtfs->drop_lock); + + if (unlikely(!xtfs->w_seq_set)) { + xtfs->w_seq_set = true; + xtfs->w_wantseq = inseq; + } + wantseq = xtfs->w_wantseq; + + if (likely(inseq == wantseq)) + __reorder_this(xtfs, inskb, list); + else if (inseq < wantseq) + __reorder_past(xtfs, inskb, freelist); + else if ((inseq - wantseq) < nslots) + __reorder_future_fits(xtfs, inskb, freelist); + else + __reorder_future_shifts(xtfs, inskb, list, freelist); } /** @@ -1192,23 +1560,90 @@ static int iptfs_input(struct xfrm_state *x, struct sk_buff *skb) */ static enum hrtimer_restart iptfs_drop_timer(struct hrtimer *me) { + struct sk_buff *skb, *next; + struct list_head freelist, list; struct xfrm_iptfs_data *xtfs; struct xfrm_state *x; + u32 count; xtfs = container_of(me, typeof(*xtfs), drop_timer); x = xtfs->x; - /* Drop any in progress packet */ spin_lock(&xtfs->drop_lock); + + INIT_LIST_HEAD(&list); + INIT_LIST_HEAD(&freelist); + + /* Drop any in progress packet */ + if (xtfs->ra_newskb) { kfree_skb(xtfs->ra_newskb); xtfs->ra_newskb = NULL; } + + /* Now drop as many packets as we should from the reordering window + * saved array + */ + count = xtfs->w_savedlen ? __reorder_drop(xtfs, &list) : 0; + spin_unlock(&xtfs->drop_lock); + if (count) { + list_for_each_entry_safe(skb, next, &list, list) { + skb_list_del_init(skb); + (void)iptfs_input_ordered(x, skb); + } + } return HRTIMER_NORESTART; } +/** + * iptfs_input() - handle receipt of iptfs payload + * @x: xfrm state + * @skb: the packet + * + * We have an IPTFS payload order it if needed, then process newly in order + * packets. + */ +static int iptfs_input(struct xfrm_state *x, struct sk_buff *skb) +{ + struct list_head freelist, list; + struct xfrm_iptfs_data *xtfs = x->mode_data; + struct sk_buff *next; + + /* Fast path for no reorder window. */ + if (xtfs->cfg.reorder_win_size == 0) { + iptfs_input_ordered(x, skb); + goto done; + } + + /* Fetch list of in-order packets from the reordering window as well as + * a list of buffers we need to now free. + */ + INIT_LIST_HEAD(&list); + INIT_LIST_HEAD(&freelist); + + spin_lock(&xtfs->drop_lock); + iptfs_input_reorder(xtfs, skb, &list, &freelist); + spin_unlock(&xtfs->drop_lock); + + list_for_each_entry_safe(skb, next, &list, list) { + skb_list_del_init(skb); + (void)iptfs_input_ordered(x, skb); + } + + list_for_each_entry_safe(skb, next, &freelist, list) { + skb_list_del_init(skb); + kfree_skb(skb); + } +done: + /* We always have dealt with the input SKB, either we are re-using it, + * or we have freed it. Return EINPROGRESS so that xfrm_input stops + * processing it. + */ + return -EINPROGRESS; +} + /* ================================= */ /* IPTFS Sending (ingress) Functions */ /* ================================= */ @@ -2013,6 +2448,7 @@ static int iptfs_user_init(struct net *net, struct xfrm_state *x, struct xfrm_iptfs_config *xc; xc = &xtfs->cfg; + xc->reorder_win_size = net->xfrm.sysctl_iptfs_reorder_window; xc->max_queue_size = net->xfrm.sysctl_iptfs_max_qsize; xtfs->init_delay_ns = (u64)net->xfrm.sysctl_iptfs_init_delay * NSECS_IN_USEC; @@ -2021,6 +2457,13 @@ static int iptfs_user_init(struct net *net, struct xfrm_state *x, if (attrs[XFRMA_IPTFS_DONT_FRAG]) xc->dont_frag = true; + if (attrs[XFRMA_IPTFS_REORDER_WINDOW]) + xc->reorder_win_size = + nla_get_u16(attrs[XFRMA_IPTFS_REORDER_WINDOW]); + /* saved array is for saving 1..N seq nums from wantseq */ + if (xc->reorder_win_size) + xtfs->w_saved = kcalloc(xc->reorder_win_size, + sizeof(*xtfs->w_saved), GFP_KERNEL); if (attrs[XFRMA_IPTFS_PKT_SIZE]) { xc->pkt_size = nla_get_u32(attrs[XFRMA_IPTFS_PKT_SIZE]); if (!xc->pkt_size) { @@ -2057,7 +2500,7 @@ static unsigned int iptfs_sa_len(const struct xfrm_state *x) if (xc->dont_frag) l += nla_total_size(0); - l += nla_total_size(sizeof(u16)); + l += nla_total_size(sizeof(xc->reorder_win_size)); l += nla_total_size(sizeof(xc->pkt_size)); l += nla_total_size(sizeof(xc->max_queue_size)); l += nla_total_size(sizeof(u32)); /* drop time usec */ @@ -2078,7 +2521,7 @@ static int iptfs_copy_to_user(struct xfrm_state *x, struct sk_buff *skb) if (ret) return ret; } - ret = nla_put_u16(skb, XFRMA_IPTFS_REORDER_WINDOW, 0); + ret = nla_put_u16(skb, XFRMA_IPTFS_REORDER_WINDOW, xc->reorder_win_size); if (ret) return ret; ret = nla_put_u32(skb, XFRMA_IPTFS_PKT_SIZE, xc->pkt_size); @@ -2140,6 +2583,14 @@ static int iptfs_clone(struct xfrm_state *x, struct xfrm_state *orig) return -ENOMEM; xtfs->ra_newskb = NULL; + if (xtfs->cfg.reorder_win_size) { + xtfs->w_saved = kcalloc(xtfs->cfg.reorder_win_size, + sizeof(*xtfs->w_saved), GFP_KERNEL); + if (!xtfs->w_saved) { + kfree_sensitive(xtfs); + return -ENOMEM; + } + } err = __iptfs_init_state(x, xtfs); if (err) @@ -2167,6 +2618,7 @@ static int iptfs_create_state(struct xfrm_state *x) static void iptfs_delete_state(struct xfrm_state *x) { struct xfrm_iptfs_data *xtfs = x->mode_data; + struct skb_wseq *s, *se; if (!xtfs) return; @@ -2179,6 +2631,11 @@ static void iptfs_delete_state(struct xfrm_state *x) if (xtfs->ra_newskb) kfree_skb(xtfs->ra_newskb); + for (s = xtfs->w_saved, se = s + xtfs->w_savedlen; s < se; s++) + if (s->skb) + kfree_skb(s->skb); + + kfree_sensitive(xtfs->w_saved); kfree_sensitive(xtfs); module_put(x->mode_cbs->owner);