From: Paolo Abeni 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 Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support") Signed-off-by: Paolo Abeni Reviewed-by: Eric Dumazet Link: https://lore.kernel.org/r/883923fa22745a9589e8610962b7dc59df09fb1f.1617981844.git.pabeni@redhat.com Signed-off-by: Jakub Kicinski --- --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6522,7 +6522,7 @@ 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 @@ -6540,6 +6540,7 @@ static int napi_thread_wait(struct napi_ set_current_state(TASK_INTERRUPTIBLE); } __set_current_state(TASK_RUNNING); + return -1; }