net: Correct wrong BH disable in hard-interrupt.

I missed the obvious case where netif_ix() is invoked from hard-IRQ
context.

Disabling bottom halves is only needed in process context. This ensures
that the code remains on the current CPU and that the soft-interrupts
are processed at local_bh_enable() time.
In hard- and soft-interrupt context this is already the case and the
soft-interrupts will be processed once the context is left (at irq-exit
time).

Disable bottom halves if neither hard-interrupts nor soft-interrupts are
disabled. Update the kernel-doc, mention that interrupts must be enabled
if invoked from process context.

Fixes: baebdf48c3600 ("net: dev: Makes sure netif_rx() can be invoked in any context.")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/Yg05duINKBqvnxUc@linutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/core/dev.c b/net/core/dev.c
index a119029..2d67710 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4860,7 +4860,9 @@ EXPORT_SYMBOL(__netif_rx);
  *     congestion control or by the protocol layers.
  *     The network buffer is passed via the backlog NAPI device. Modern NIC
  *     driver should use NAPI and GRO.
- *     This function can used from any context.
+ *     This function can used from interrupt and from process context. The
+ *     caller from process context must not disable interrupts before invoking
+ *     this function.
  *
  *     return values:
  *     NET_RX_SUCCESS  (no congestion)
@@ -4869,13 +4871,16 @@ EXPORT_SYMBOL(__netif_rx);
  */
 int netif_rx(struct sk_buff *skb)
 {
+       bool need_bh_off = !(hardirq_count() | softirq_count());
        int ret;
 
-       local_bh_disable();
+       if (need_bh_off)
+               local_bh_disable();
        trace_netif_rx_entry(skb);
        ret = netif_rx_internal(skb);
        trace_netif_rx_exit(ret);
-       local_bh_enable();
+       if (need_bh_off)
+               local_bh_enable();
        return ret;
 }
 EXPORT_SYMBOL(netif_rx);