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 <k...@kernel.org>
Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support")
Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
net/core/dev.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index 0f72ff5d34ba..af8c1ea040b9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6992,7 +6992,7 @@ static int napi_thread_wait(struct napi_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
@@ -7010,6 +7010,7 @@ static int napi_thread_wait(struct napi_struct *napi)
set_current_state(TASK_INTERRUPTIBLE);
}
__set_current_state(TASK_RUNNING);
+
return -1;
}
--
2.26.2
