From: Xuan Zhuo xuanzhuo@linux.alibaba.com
[ Upstream commit 3765996e4f0b8a755cab215a08df744490c76052 ]
The process will cause napi.state to contain NAPI_STATE_SCHED and not in the poll_list, which will cause napi_disable() to get stuck.
The prefix "NAPI_STATE_" is removed in the figure below, and NAPI_STATE_HASHED is ignored in napi.state.
CPU0 | CPU1 | napi.state =============================================================================== napi_disable() | | SCHED | NPSVC napi_enable() | | { | | smp_mb__before_atomic(); | | clear_bit(SCHED, &n->state); | | NPSVC | napi_schedule_prep() | SCHED | NPSVC | napi_poll() | | napi_complete_done() | | { | | if (n->state & (NPSVC | | (1) | _BUSY_POLL))) | | return false; | | ................ | | } | SCHED | NPSVC | | clear_bit(NPSVC, &n->state); | | SCHED } | | | | napi_schedule_prep() | | SCHED | MISSED (2)
(1) Here return direct. Because of NAPI_STATE_NPSVC exists. (2) NAPI_STATE_SCHED exists. So not add napi.poll_list to sd->poll_list
Since NAPI_STATE_SCHED already exists and napi is not in the sd->poll_list queue, NAPI_STATE_SCHED cannot be cleared and will always exist.
1. This will cause this queue to no longer receive packets. 2. If you encounter napi_disable under the protection of rtnl_lock, it will cause the entire rtnl_lock to be locked, affecting the overall system.
This patch uses cmpxchg to implement napi_enable(), which ensures that there will be no race due to the separation of clear two bits.
Fixes: 2d8bff12699abc ("netpoll: Close race condition between poll_one_napi and napi_disable") Signed-off-by: Xuan Zhuo xuanzhuo@linux.alibaba.com Reviewed-by: Dust Li dust.li@linux.alibaba.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/dev.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c index 8f1a47ad6781..693f15a05630 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6988,12 +6988,16 @@ EXPORT_SYMBOL(napi_disable); */ void napi_enable(struct napi_struct *n) { - BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state)); - smp_mb__before_atomic(); - clear_bit(NAPI_STATE_SCHED, &n->state); - clear_bit(NAPI_STATE_NPSVC, &n->state); - if (n->dev->threaded && n->thread) - set_bit(NAPI_STATE_THREADED, &n->state); + unsigned long val, new; + + do { + val = READ_ONCE(n->state); + BUG_ON(!test_bit(NAPI_STATE_SCHED, &val)); + + new = val & ~(NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC); + if (n->dev->threaded && n->thread) + new |= NAPIF_STATE_THREADED; + } while (cmpxchg(&n->state, val, new) != val); } EXPORT_SYMBOL(napi_enable);