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- From: Wei Wang <[email protected]>
- Date: Mon, 1 Mar 2021 17:21:13 -0800
- Subject: [PATCH] net: fix race between napi kthread mode and busy poll
- Currently, napi_thread_wait() checks for NAPI_STATE_SCHED bit to
- determine if the kthread owns this napi and could call napi->poll() on
- it. However, if socket busy poll is enabled, it is possible that the
- busy poll thread grabs this SCHED bit (after the previous napi->poll()
- invokes napi_complete_done() and clears SCHED bit) and tries to poll
- on the same napi. napi_disable() could grab the SCHED bit as well.
- This patch tries to fix this race by adding a new bit
- NAPI_STATE_SCHED_THREADED in napi->state. This bit gets set in
- ____napi_schedule() if the threaded mode is enabled, and gets cleared
- in napi_complete_done(), and we only poll the napi in kthread if this
- bit is set. This helps distinguish the ownership of the napi between
- kthread and other scenarios and fixes the race issue.
- Fixes: 29863d41bb6e ("net: implement threaded-able napi poll loop support")
- Reported-by: Martin Zaharinov <[email protected]>
- Suggested-by: Jakub Kicinski <[email protected]>
- Signed-off-by: Wei Wang <[email protected]>
- Cc: Alexander Duyck <[email protected]>
- Cc: Eric Dumazet <[email protected]>
- Cc: Paolo Abeni <[email protected]>
- Cc: Hannes Frederic Sowa <[email protected]>
- ---
- --- a/include/linux/netdevice.h
- +++ b/include/linux/netdevice.h
- @@ -359,6 +359,7 @@ enum {
- NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */
- NAPI_STATE_IN_BUSY_POLL,/* sk_busy_loop() owns this NAPI */
- NAPI_STATE_THREADED, /* The poll is performed inside its own thread*/
- + NAPI_STATE_SCHED_THREADED, /* Napi is currently scheduled in threaded mode */
- };
-
- enum {
- @@ -370,6 +371,7 @@ enum {
- NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL),
- NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
- NAPIF_STATE_THREADED = BIT(NAPI_STATE_THREADED),
- + NAPIF_STATE_SCHED_THREADED = BIT(NAPI_STATE_SCHED_THREADED),
- };
-
- enum gro_result {
- --- a/net/core/dev.c
- +++ b/net/core/dev.c
- @@ -4304,6 +4304,8 @@ static inline void ____napi_schedule(str
- */
- thread = READ_ONCE(napi->thread);
- if (thread) {
- + if (thread->state != TASK_INTERRUPTIBLE)
- + set_bit(NAPI_STATE_SCHED_THREADED, &napi->state);
- wake_up_process(thread);
- return;
- }
- @@ -6564,7 +6566,8 @@ bool napi_complete_done(struct napi_stru
-
- WARN_ON_ONCE(!(val & NAPIF_STATE_SCHED));
-
- - new = val & ~(NAPIF_STATE_MISSED | NAPIF_STATE_SCHED);
- + new = val & ~(NAPIF_STATE_MISSED | NAPIF_STATE_SCHED |
- + NAPIF_STATE_SCHED_THREADED);
-
- /* If STATE_MISSED was set, leave STATE_SCHED set,
- * because we will call napi->poll() one more time.
- @@ -7000,16 +7003,25 @@ static int napi_poll(struct napi_struct
-
- static int napi_thread_wait(struct napi_struct *napi)
- {
- + bool woken = false;
- +
- set_current_state(TASK_INTERRUPTIBLE);
-
- while (!kthread_should_stop() && !napi_disable_pending(napi)) {
- - if (test_bit(NAPI_STATE_SCHED, &napi->state)) {
- + /* 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
- + * set by some other busy poll thread or by napi_disable().
- + */
- + if (test_bit(NAPI_STATE_SCHED_THREADED, &napi->state) || woken) {
- WARN_ON(!list_empty(&napi->poll_list));
- __set_current_state(TASK_RUNNING);
- return 0;
- }
-
- schedule();
- + /* woken being true indicates this thread owns this napi. */
- + woken = true;
- set_current_state(TASK_INTERRUPTIBLE);
- }
- __set_current_state(TASK_RUNNING);
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