[PATCH net] net: ps3_gelic_net: handle skb allocation failures

[Florian Fuchs]

Handle skb allocation failures in RX path, to avoid NULL pointer
dereference and RX stalls under memory pressure. If the refill fails
with -ENOMEM, complete napi polling and wake up later to retry via timer.
Also explicitly re-enable RX DMA after oom, so the dmac doesn't remain
stopped in this situation.

Previously, memory pressure could lead to skb allocation failures and
subsequent Oops like:

	Oops: Kernel access of bad area, sig: 11 [#2]
	Hardware name: SonyPS3 Cell Broadband Engine 0x701000 PS3
	NIP [c0003d0000065900] gelic_net_poll+0x6c/0x2d0 [ps3_gelic] (unreliable)
	LR [c0003d00000659c4] gelic_net_poll+0x130/0x2d0 [ps3_gelic]
	Call Trace:
	  gelic_net_poll+0x130/0x2d0 [ps3_gelic] (unreliable)
	  __napi_poll+0x44/0x168
	  net_rx_action+0x178/0x290

Steps to reproduce the issue:
	1. Start a continuous network traffic, like scp of a 20GB file
	2. Inject failslab errors using the kernel fault injection:
	    echo -1 > /sys/kernel/debug/failslab/times
	    echo 30 > /sys/kernel/debug/failslab/interval
	    echo 100 > /sys/kernel/debug/failslab/probability
	3. After some time, traces start to appear, kernel Oopses
	   and the system stops

Step 2 is not always necessary, as it is usually already triggered by
the transfer of a big enough file.

Fixes: 02c1889166b4 ("ps3: gigabit ethernet driver for PS3, take3")
Signed-off-by: Florian Fuchs <fuchsfl at gmail.com>
---
 drivers/net/ethernet/toshiba/ps3_gelic_net.c | 54 +++++++++++++++-----
 drivers/net/ethernet/toshiba/ps3_gelic_net.h |  1 +
 2 files changed, 42 insertions(+), 13 deletions(-)

diff --git a/drivers/net/ethernet/toshiba/ps3_gelic_net.c b/drivers/net/ethernet/toshiba/ps3_gelic_net.c
index 5ee8e8980393..a8121f7583f9 100644
--- a/drivers/net/ethernet/toshiba/ps3_gelic_net.c
+++ b/drivers/net/ethernet/toshiba/ps3_gelic_net.c
@@ -259,6 +259,7 @@ void gelic_card_down(struct gelic_card *card)
 	mutex_lock(&card->updown_lock);
 	if (atomic_dec_if_positive(&card->users) == 0) {
 		pr_debug("%s: real do\n", __func__);
+		timer_delete_sync(&card->rx_oom_timer);
 		napi_disable(&card->napi);
 		/*
 		 * Disable irq. Wireless interrupts will
@@ -970,7 +971,8 @@ static void gelic_net_pass_skb_up(struct gelic_descr *descr,
  * gelic_card_decode_one_descr - processes an rx descriptor
  * @card: card structure
  *
- * returns 1 if a packet has been sent to the stack, otherwise 0
+ * returns 1 if a packet has been sent to the stack, -ENOMEM on skb alloc
+ * failure, otherwise 0
  *
  * processes an rx descriptor by iommu-unmapping the data buffer and passing
  * the packet up to the stack
@@ -981,16 +983,17 @@ static int gelic_card_decode_one_descr(struct gelic_card *card)
 	struct gelic_descr_chain *chain = &card->rx_chain;
 	struct gelic_descr *descr = chain->head;
 	struct net_device *netdev = NULL;
-	int dmac_chain_ended;
+	int dmac_chain_ended = 0;
 
 	status = gelic_descr_get_status(descr);
 
 	if (status == GELIC_DESCR_DMA_CARDOWNED)
 		return 0;
 
-	if (status == GELIC_DESCR_DMA_NOT_IN_USE) {
+	if (status == GELIC_DESCR_DMA_NOT_IN_USE || !descr->skb) {
 		dev_dbg(ctodev(card), "dormant descr? %p\n", descr);
-		return 0;
+		dmac_chain_ended = 1;
+		goto refill;
 	}
 
 	/* netdevice select */
@@ -1048,9 +1051,10 @@ static int gelic_card_decode_one_descr(struct gelic_card *card)
 refill:
 
 	/* is the current descriptor terminated with next_descr == NULL? */
-	dmac_chain_ended =
-		be32_to_cpu(descr->hw_regs.dmac_cmd_status) &
-		GELIC_DESCR_RX_DMA_CHAIN_END;
+	if (!dmac_chain_ended)
+		dmac_chain_ended =
+			be32_to_cpu(descr->hw_regs.dmac_cmd_status) &
+			GELIC_DESCR_RX_DMA_CHAIN_END;
 	/*
 	 * So that always DMAC can see the end
 	 * of the descriptor chain to avoid
@@ -1062,10 +1066,12 @@ static int gelic_card_decode_one_descr(struct gelic_card *card)
 	gelic_descr_set_status(descr, GELIC_DESCR_DMA_NOT_IN_USE);
 
 	/*
-	 * this call can fail, but for now, just leave this
-	 * descriptor without skb
+	 * this call can fail, propagate the error
 	 */
-	gelic_descr_prepare_rx(card, descr);
+	int ret = gelic_descr_prepare_rx(card, descr);
+
+	if (ret)
+		return ret;
 
 	chain->tail = descr;
 	chain->head = descr->next;
@@ -1087,6 +1093,17 @@ static int gelic_card_decode_one_descr(struct gelic_card *card)
 	return 1;
 }
 
+/**
+ *  gelic_rx_oom_timer - Restart napi poll if oom occurred
+ *  @t: timer list
+ */
+static void gelic_rx_oom_timer(struct timer_list *t)
+{
+	struct gelic_card *card = timer_container_of(card, t, rx_oom_timer);
+
+	napi_schedule(&card->napi);
+}
+
 /**
  * gelic_net_poll - NAPI poll function called by the stack to return packets
  * @napi: napi structure
@@ -1099,12 +1116,21 @@ static int gelic_net_poll(struct napi_struct *napi, int budget)
 {
 	struct gelic_card *card = container_of(napi, struct gelic_card, napi);
 	int packets_done = 0;
+	int work_result = 0;
 
 	while (packets_done < budget) {
-		if (!gelic_card_decode_one_descr(card))
-			break;
+		work_result = gelic_card_decode_one_descr(card);
+		if (work_result == 1) {
+			packets_done++;
+			continue;
+		}
+		break;
+	}
 
-		packets_done++;
+	if (work_result == -ENOMEM) {
+		napi_complete_done(napi, packets_done);
+		mod_timer(&card->rx_oom_timer, jiffies + 1);
+		return packets_done;
 	}
 
 	if (packets_done < budget) {
@@ -1576,6 +1602,8 @@ static struct gelic_card *gelic_alloc_card_net(struct net_device **netdev)
 	mutex_init(&card->updown_lock);
 	atomic_set(&card->users, 0);
 
+	timer_setup(&card->rx_oom_timer, gelic_rx_oom_timer, 0);
+
 	return card;
 }
 
diff --git a/drivers/net/ethernet/toshiba/ps3_gelic_net.h b/drivers/net/ethernet/toshiba/ps3_gelic_net.h
index f7d7931e51b7..c10f1984a5a1 100644
--- a/drivers/net/ethernet/toshiba/ps3_gelic_net.h
+++ b/drivers/net/ethernet/toshiba/ps3_gelic_net.h
@@ -268,6 +268,7 @@ struct gelic_vlan_id {
 struct gelic_card {
 	struct napi_struct napi;
 	struct net_device *netdev[GELIC_PORT_MAX];
+	struct timer_list rx_oom_timer;
 	/*
 	 * hypervisor requires irq_status should be
 	 * 8 bytes aligned, but u64 member is

base-commit: 96a9178a29a6b84bb632ebeb4e84cf61191c73d5
-- 
2.43.0