From git@z Thu Jan 1 00:00:00 1970 Subject: [PATCH v2] net: make napi_disable() symmetric with enable From: Jakub Kicinski Date: Fri, 24 Sep 2021 13:24:53 -0700 Message-Id: <20210924202453.1051687-1-kuba@kernel.org> To: davem@davemloft.net Cc: netdev@vger.kernel.org, eric.dumazet@gmail.com, weiwan@google.com, xuanzhuo@linux.alibaba.com, Jakub Kicinski List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Commit 3765996e4f0b ("napi: fix race inside napi_enable") fixed an ordering bug in napi_enable() and made the napi_enable() diverge from napi_disable(). The state transitions done on disable are not symmetric to enable. There is no known bug in napi_disable() this is just refactoring. Eric suggests we can also replace msleep(1) with a more opportunistic usleep_range(). Signed-off-by: Jakub Kicinski --- net/core/dev.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index f24c3a9..f0a556a 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6386,18 +6386,25 @@ EXPORT_SYMBOL(netif_napi_add); void napi_disable(struct napi_struct *n) { + unsigned long val, new; + might_sleep(); set_bit(NAPI_STATE_DISABLE, &n->state); - while (test_and_set_bit(NAPI_STATE_SCHED, &n->state)) - msleep(1); - while (test_and_set_bit(NAPI_STATE_NPSVC, &n->state)) - msleep(1); + do { + val = READ_ONCE(n->state); + if (val & (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC)) { + usleep_range(20, 200); + continue; + } + + new = val | NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC; + new &= ~(NAPIF_STATE_THREADED); + } while (cmpxchg(&n->state, val, new) != val); hrtimer_cancel(&n->timer); clear_bit(NAPI_STATE_DISABLE, &n->state); - clear_bit(NAPI_STATE_THREADED, &n->state); } EXPORT_SYMBOL(napi_disable); -- 2.31.1