net: rfs: fix crash in get_rps_cpus()

Commit 567e4b79731c ("net: rfs: add hash collision detection") had one
mistake :

RPS_NO_CPU is no longer the marker for invalid cpu in set_rps_cpu()
and get_rps_cpu(), as @next_cpu was the result of an AND with
rps_cpu_mask

This bug showed up on a host with 72 cpus :
next_cpu was 0x7f, and the code was trying to access percpu data of an
non existent cpu.

In a follow up patch, we might get rid of compares against nr_cpu_ids,
if we init the tables with 0. This is silly to test for a very unlikely
condition that exists only shortly after table initialization, as
we got rid of rps_reset_sock_flow() and similar functions that were
writing this RPS_NO_CPU magic value at flow dismantle : When table is
old enough, it never contains this value anymore.

Fixes: 567e4b79731c ("net: rfs: add hash collision detection")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/networking/scaling.txt b/Documentation/networking/scaling.txt
index cbfac09..59f4db2 100644 (file)
--- a/Documentation/networking/scaling.txt
+++ b/Documentation/networking/scaling.txt
@@ -282,7 +282,7 @@ following is true:
 
 - The current CPU's queue head counter >= the recorded tail counter
   value in rps_dev_flow[i]
-- The current CPU is unset (equal to RPS_NO_CPU)
+- The current CPU is unset (>= nr_cpu_ids)
 - The current CPU is offline
 
 After this check, the packet is sent to the (possibly updated) current

diff --git a/net/core/dev.c b/net/core/dev.c
index 1796cef..c7ba038 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3079,7 +3079,7 @@ static struct rps_dev_flow *
 set_rps_cpu(struct net_device *dev, struct sk_buff *skb,
            struct rps_dev_flow *rflow, u16 next_cpu)
 {
-       if (next_cpu != RPS_NO_CPU) {
+       if (next_cpu < nr_cpu_ids) {
 #ifdef CONFIG_RFS_ACCEL
                struct netdev_rx_queue *rxqueue;
                struct rps_dev_flow_table *flow_table;
@@ -3184,7 +3184,7 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
                 * If the desired CPU (where last recvmsg was done) is
                 * different from current CPU (one in the rx-queue flow
                 * table entry), switch if one of the following holds:
-                *   - Current CPU is unset (equal to RPS_NO_CPU).
+                *   - Current CPU is unset (>= nr_cpu_ids).
                 *   - Current CPU is offline.
                 *   - The current CPU's queue tail has advanced beyond the
                 *     last packet that was enqueued using this table entry.
@@ -3192,14 +3192,14 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
                 *     have been dequeued, thus preserving in order delivery.
                 */
                if (unlikely(tcpu != next_cpu) &&
-                   (tcpu == RPS_NO_CPU || !cpu_online(tcpu) ||
+                   (tcpu >= nr_cpu_ids || !cpu_online(tcpu) ||
                     ((int)(per_cpu(softnet_data, tcpu).input_queue_head -
                      rflow->last_qtail)) >= 0)) {
                        tcpu = next_cpu;
                        rflow = set_rps_cpu(dev, skb, rflow, next_cpu);
                }
 
-               if (tcpu != RPS_NO_CPU && cpu_online(tcpu)) {
+               if (tcpu < nr_cpu_ids && cpu_online(tcpu)) {
                        *rflowp = rflow;
                        cpu = tcpu;
                        goto done;
@@ -3240,14 +3240,14 @@ bool rps_may_expire_flow(struct net_device *dev, u16 rxq_index,
        struct rps_dev_flow_table *flow_table;
        struct rps_dev_flow *rflow;
        bool expire = true;
-       int cpu;
+       unsigned int cpu;
 
        rcu_read_lock();
        flow_table = rcu_dereference(rxqueue->rps_flow_table);
        if (flow_table && flow_id <= flow_table->mask) {
                rflow = &flow_table->flows[flow_id];
                cpu = ACCESS_ONCE(rflow->cpu);
-               if (rflow->filter == filter_id && cpu != RPS_NO_CPU &&
+               if (rflow->filter == filter_id && cpu < nr_cpu_ids &&
                    ((int)(per_cpu(softnet_data, cpu).input_queue_head -
                           rflow->last_qtail) <
                     (int)(10 * flow_table->mask)))