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- From: Paolo Abeni <[email protected]>
- Date: Fri, 9 Apr 2021 17:24:17 +0200
- Subject: [PATCH] net: fix hangup on napi_disable for threaded napi
- napi_disable() is subject to an hangup, when the threaded
- mode is enabled and the napi is under heavy traffic.
- If the relevant napi has been scheduled and the napi_disable()
- kicks in before the next napi_threaded_wait() completes - so
- that the latter quits due to the napi_disable_pending() condition,
- the existing code leaves the NAPI_STATE_SCHED bit set and the
- napi_disable() loop waiting for such bit will hang.
- This patch addresses the issue by dropping the NAPI_STATE_DISABLE
- bit test in napi_thread_wait(). The later napi_threaded_poll()
- iteration will take care of clearing the NAPI_STATE_SCHED.
- This also addresses a related problem reported by Jakub:
- before this patch a napi_disable()/napi_enable() pair killed
- the napi thread, effectively disabling the threaded mode.
- On the patched kernel napi_disable() simply stops scheduling
- the relevant thread.
- v1 -> v2:
- - let the main napi_thread_poll() loop clear the SCHED bit
- Reported-by: Jakub Kicinski <[email protected]>
- Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support")
- Signed-off-by: Paolo Abeni <[email protected]>
- Reviewed-by: Eric Dumazet <[email protected]>
- Link: https://lore.kernel.org/r/883923fa22745a9589e8610962b7dc59df09fb1f.1617981844.git.pabeni@redhat.com
- Signed-off-by: Jakub Kicinski <[email protected]>
- ---
- --- a/net/core/dev.c
- +++ b/net/core/dev.c
- @@ -7007,7 +7007,7 @@ static int napi_thread_wait(struct napi_
-
- set_current_state(TASK_INTERRUPTIBLE);
-
- - while (!kthread_should_stop() && !napi_disable_pending(napi)) {
- + while (!kthread_should_stop()) {
- /* Testing SCHED_THREADED bit here to make sure the current
- * kthread owns this napi and could poll on this napi.
- * Testing SCHED bit is not enough because SCHED bit might be
- @@ -7025,6 +7025,7 @@ static int napi_thread_wait(struct napi_
- set_current_state(TASK_INTERRUPTIBLE);
- }
- __set_current_state(TASK_RUNNING);
- +
- return -1;
- }
-
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