When in a softirq context, memory allocation should be atomic

Eviction of flows based on TCP state machine happens in the softirq
context. The process of evicting a flow depends on the kernel work
queues, for which allocation of memory needs to happen. Under such
cases, the allocation should not wait. Hence, pass GFP_ATOMIC as the
allocation flag when in softirq context to indicate that the path is
not willing to block.

Change-Id: I2c56203c2666a981ff3218268611d95e18281151
Closes-Bug: #1618375

dp-core/vr_flow.c

@@ -1714,8 +1714,7 @@ __vr_flow_schedule_transition(struct vrouter *router, struct vr_flow_entry *fe,
     }
     flmd->flmd_defer_data = defer;
 
-    vr_schedule_work(vr_get_cpu(), vr_flow_work, (void *)flmd);
-    return 0;
+    return vr_schedule_work(vr_get_cpu(), vr_flow_work, (void *)flmd);
 }
 
 static int

dpdk/vr_dpdk_host.c

@@ -502,11 +502,13 @@ dpdk_get_mono_time(unsigned int *sec, unsigned int *nsec)
 }
 
 /* Work callback called on NetLink lcore */
-static void
+static int
 dpdk_schedule_work(unsigned int cpu, void (*fn)(void *), void *arg)
 {
     /* no RCU reader lock needed, just do the work */
     fn(arg);
+
+    return 0;
 }
 
 static void

freebsd/vrouter_mod.c

@@ -331,11 +331,12 @@ fh_get_cpu(void)
 	return (cpuid);
 }
 
-static void
+static int
 fh_schedule_work(unsigned int cpu, void (*fn)(void *), void *arg)
 {
-
 	vr_log(VR_ERR, "%s: not implemented\n", __func__);
+
+    return -EOPNOTSUPP;
 }
 
 static void

host/vrouter_host_mod.c

@@ -225,10 +225,10 @@ vr_lib_get_cpu(void)
     return 0;
 }
 
-static void
+static int
 vr_lib_schedule_work(unsigned int cpu, void (*fn)(void *), void *arg)
 {
-    return;
+    return -EOPNOTSUPP;
 }
 
 static void

include/vrouter.h

@@ -159,7 +159,7 @@ struct host_os {
     unsigned int (*hos_pgso_size)(struct vr_packet *);
 
     unsigned int (*hos_get_cpu)(void);
-    void (*hos_schedule_work)(unsigned int, void (*)(void *), void *);
+    int (*hos_schedule_work)(unsigned int, void (*)(void *), void *);
     void (*hos_delay_op)(void);
     void (*hos_defer)(struct vrouter *, vr_defer_cb, void *);
     void *(*hos_get_defer_data)(unsigned int);

linux/vrouter_mod.c

@@ -416,20 +416,28 @@ lh_work(struct work_struct *work)
     return;
 }
 
-static void
+static int
 lh_schedule_work(unsigned int cpu, void (*fn)(void *), void *arg)
 {
-    struct work_arg *wa = kzalloc(sizeof(*wa), GFP_KERNEL);
+    unsigned int alloc_flag;
+    struct work_arg *wa;
+
+    if (in_softirq()) {
+        alloc_flag = GFP_ATOMIC;
+    } else {
+        alloc_flag = GFP_KERNEL;
+    }
 
+    wa = kzalloc(sizeof(*wa), alloc_flag);
     if (!wa)
-        return;
+        return -ENOMEM;
 
     wa->fn = fn;
     wa->wa_arg = arg;
     INIT_WORK(&wa->wa_work, lh_work);
     schedule_work_on(cpu, &wa->wa_work);
 
-    return;
+    return 0;
 }
 
 static void