Re: [PATCH net-next] net: Correct wrong BH disable in hard-interrupt.

Hi All,

On 17.02.2022 07:35, Marek Szyprowski wrote:

Hi Andrzej,

On 16.02.2022 18:50, Sebastian Andrzej Siewior wrote:

quoted

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>
---
Marek, does this work for you?

Yes, this fixed the issue. Thanks!

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

I've just noticed that there is one more issue left to fix (the $subject 
patch is already applied) - this one comes from threaded irq (if I got 
the stack trace right):

------------[ cut here ]------------
WARNING: CPU: 0 PID: 147 at kernel/softirq.c:363 
__local_bh_enable_ip+0xa8/0x1c0
Modules linked in: cpufreq_powersave cpufreq_conservative brcmfmac 
brcmutil cfg80211 s3fwrn5_i2c s3fwrn5 nci crct10dif_ce exynos_gsc nfc 
s5p_jpeg hci_uart btqca s
5p_mfc v4l2_mem2mem btbcm bluetooth videobuf2_dma_contig 
videobuf2_memops ecdh_generic videobuf2_v4l2 panfrost drm_shmem_helper 
ecc videobuf2_common gpu_sched rfkill videodev mc ip_tables x_tab
les ipv6
CPU: 0 PID: 147 Comm: irq/150-dwc3 Not tainted 5.17.0-rc4-next-20220217+ 
#4557
Hardware name: Samsung TM2E board (DT)
pstate: 400000c5 (nZcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __local_bh_enable_ip+0xa8/0x1c0
lr : netif_rx+0xa4/0x2c0
...

Call trace:
  __local_bh_enable_ip+0xa8/0x1c0
  netif_rx+0xa4/0x2c0
  rx_complete+0x214/0x250
  usb_gadget_giveback_request+0x58/0x170
  dwc3_gadget_giveback+0xe4/0x200
  dwc3_gadget_endpoint_trbs_complete+0x100/0x388
  dwc3_thread_interrupt+0x46c/0xe20
  irq_thread_fn+0x28/0x98
  irq_thread+0x184/0x238
  kthread+0x100/0x120
  ret_from_fork+0x10/0x20
irq event stamp: 645
hardirqs last  enabled at (643): [<ffff8000080c93b8>] 
finish_task_switch+0x98/0x288
hardirqs last disabled at (644): [<ffff8000090a6e34>] 
_raw_spin_lock_irqsave+0xb4/0x148
softirqs last  enabled at (252): [<ffff800008010488>] _stext+0x488/0x5cc
softirqs last disabled at (645): [<ffff800008ed71b0>] netif_rx+0x188/0x2c0
---[ end trace 0000000000000000 ]---

quoted

  net/core/dev.c | 11 ++++++++---
  1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 909fb38159108..87729491460fc 100644
--- 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)

@@ -4870,12 +4872,15 @@ EXPORT_SYMBOL(__netif_rx);

  int netif_rx(struct sk_buff *skb)
  {
      int ret;
+    bool need_bh_off = !(hardirq_count() | softirq_count());
  -    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);

Best regards

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland