kernel: add workaround for page_pool_release warnings

defer_list skbs held by NAPI can block releasing page pools.
Work around this by scheduling rx softirq on all CPUs while trying to release
a page pool.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

diff --git a/target/linux/generic/hack-6.6/610-net-page_pool-try-to-free-deferred-skbs-while-waitin.patch b/target/linux/generic/hack-6.6/610-net-page_pool-try-to-free-deferred-skbs-while-waitin.patch
new file mode 100644 (file)
index 0000000..36c28b9
--- /dev/null
+++ b/target/linux/generic/hack-6.6/610-net-page_pool-try-to-free-deferred-skbs-while-waitin.patch
@@ -0,0 +1,43 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Fri, 3 Jan 2025 19:29:00 +0100
+Subject: [PATCH] net: page_pool: try to free deferred skbs while waiting for
+ pool release
+
+The NAPI defer list can accumulate no longer used skbs, which can be reused
+during alloc. If this happens on a CPU that otherwise does not do any
+rx softirq processing, skbs can be held indefinitely, causing warnings
+on releasing page pools.
+Deal with this by scheduling rx softirq on all CPUs.
+
+Patch by Lorenzo Bianconi
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/core/page_pool.c
++++ b/net/core/page_pool.c
+@@ -862,12 +862,23 @@ static void page_pool_release_retry(stru
+ {
+       struct delayed_work *dwq = to_delayed_work(wq);
+       struct page_pool *pool = container_of(dwq, typeof(*pool), release_dw);
+-      int inflight;
++      int cpu, inflight;
+ 
+       inflight = page_pool_release(pool);
+       if (!inflight)
+               return;
+ 
++      /* Run NET_RX_SOFTIRQ in order to free pending skbs in softnet_data
++       * defer_list that can stay in the list until we have enough queued
++       * traffic.
++       */
++      for_each_online_cpu(cpu) {
++              struct softnet_data *sd = &per_cpu(softnet_data, cpu);
++
++              if (!cmpxchg(&sd->defer_ipi_scheduled, 0, 1))
++                      smp_call_function_single_async(cpu, &sd->defer_csd);
++      }
++
+       /* Periodic warning */
+       if (time_after_eq(jiffies, pool->defer_warn)) {
+               int sec = (s32)((u32)jiffies - (u32)pool->defer_start) / HZ;