target/linux/generic/backport-5.10/604-v5.12-net-fix-hangup-on-napi_disable-for-threaded-napi.patch

   1 From: Paolo Abeni <pabeni@redhat.com>
   2 Date: Fri, 9 Apr 2021 17:24:17 +0200
   3 Subject: [PATCH] net: fix hangup on napi_disable for threaded napi
   4
   5 napi_disable() is subject to an hangup, when the threaded
   6 mode is enabled and the napi is under heavy traffic.
   7
   8 If the relevant napi has been scheduled and the napi_disable()
   9 kicks in before the next napi_threaded_wait() completes - so
  10 that the latter quits due to the napi_disable_pending() condition,
  11 the existing code leaves the NAPI_STATE_SCHED bit set and the
  12 napi_disable() loop waiting for such bit will hang.
  13
  14 This patch addresses the issue by dropping the NAPI_STATE_DISABLE
  15 bit test in napi_thread_wait(). The later napi_threaded_poll()
  16 iteration will take care of clearing the NAPI_STATE_SCHED.
  17
  18 This also addresses a related problem reported by Jakub:
  19 before this patch a napi_disable()/napi_enable() pair killed
  20 the napi thread, effectively disabling the threaded mode.
  21 On the patched kernel napi_disable() simply stops scheduling
  22 the relevant thread.
  23
  24 v1 -> v2:
  25   - let the main napi_thread_poll() loop clear the SCHED bit
  26
  27 Reported-by: Jakub Kicinski <kuba@kernel.org>
  28 Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support")
  29 Signed-off-by: Paolo Abeni <pabeni@redhat.com>
  30 Reviewed-by: Eric Dumazet <edumazet@google.com>
  31 Link: https://lore.kernel.org/r/883923fa22745a9589e8610962b7dc59df09fb1f.1617981844.git.pabeni@redhat.com
  32 Signed-off-by: Jakub Kicinski <kuba@kernel.org>
  33 ---
  34
  35 --- a/net/core/dev.c
  36 +++ b/net/core/dev.c
  37 @@ -7003,7 +7003,7 @@ static int napi_thread_wait(struct napi_
  38
  39         set_current_state(TASK_INTERRUPTIBLE);
  40
  41 -       while (!kthread_should_stop() && !napi_disable_pending(napi)) {
  42 +       while (!kthread_should_stop()) {
  43                 /* Testing SCHED_THREADED bit here to make sure the current
  44                  * kthread owns this napi and could poll on this napi.
  45                  * Testing SCHED bit is not enough because SCHED bit might be
  46 @@ -7021,6 +7021,7 @@ static int napi_thread_wait(struct napi_
  47                 set_current_state(TASK_INTERRUPTIBLE);
  48         }
  49         __set_current_state(TASK_RUNNING);
  50 +
  51         return -1;
  52  }
  53