Return-path: Received: from nbd.name ([46.4.11.11]:46458 "EHLO nbd.name" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932216AbcLMKlS (ORCPT ); Tue, 13 Dec 2016 05:41:18 -0500 Subject: Re: [PATCH] ath9k: unlock rcu read when returning early To: Tobias Klausmann , kvalo@codeaurora.org, helgaas@kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, marc.zyngier@arm.com, Janusz.Dziedzic@tieto.com, rmanohar@qti.qualcomm.com, ath9k-devel@qca.qualcomm.com, linux-wireless@vger.kernel.org, rmanohar@qca.qualcomm.com, bharat.kumar.gogada@xilinx.com References: <1cFMHb-00BdWd-Ks> <20161212185001.3857-1-tobias.johannes.klausmann@mni.thm.de> From: Felix Fietkau Message-ID: (sfid-20161213_114149_916703_BFC7DAE1) Date: Tue, 13 Dec 2016 11:41:07 +0100 MIME-Version: 1.0 In-Reply-To: <20161212185001.3857-1-tobias.johannes.klausmann@mni.thm.de> Content-Type: text/plain; charset=utf-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On 2016-12-12 19:50, Tobias Klausmann wrote: > Starting with ath9k: use ieee80211_tx_status_noskb where possible > [d94a461d7a7df68991fb9663531173f60ef89c68] the driver uses rcu_read_lock() && > rcu_read_unlock() yet on returning early in ath_tx_edma_tasklet() the unlock is > missing leading to stalls and suspicious RCU usage: > > =============================== > [ INFO: suspicious RCU usage. ] > 4.9.0-rc8 #11 Not tainted > ------------------------------- > kernel/rcu/tree.c:705 Illegal idle entry in RCU read-side critical section.! > > other info that might help us debug this: > > RCU used illegally from idle CPU! > rcu_scheduler_active = 1, debug_locks = 0 > RCU used illegally from extended quiescent state! > 1 lock held by swapper/7/0: > #0: > ( > rcu_read_lock > ){......} > , at: > [] ath_tx_edma_tasklet+0x0/0x450 [ath9k] > > stack backtrace: > CPU: 7 PID: 0 Comm: swapper/7 Not tainted 4.9.0-rc8 #11 > Hardware name: Acer Aspire V3-571G/VA50_HC_CR, BIOS V2.21 12/16/2013 > ffff88025efc3f38 ffffffff8132b1e5 ffff88017ede4540 0000000000000001 > ffff88025efc3f68 ffffffff810a25f7 ffff88025efcee60 ffff88017edebdd8 > ffff88025eeb5400 0000000000000091 ffff88025efc3f88 ffffffff810c3cd4 > Call Trace: > > [] dump_stack+0x68/0x93 > [] lockdep_rcu_suspicious+0xd7/0x110 > [] rcu_eqs_enter_common.constprop.85+0x154/0x200 > [] rcu_irq_exit+0x44/0xa0 > [] irq_exit+0x61/0xd0 > [] do_IRQ+0x65/0x110 > [] common_interrupt+0x89/0x89 > > [] ? cpuidle_enter_state+0x151/0x200 > [] cpuidle_enter+0x12/0x20 > [] call_cpuidle+0x1e/0x40 > [] cpu_startup_entry+0x146/0x220 > [] start_secondary+0x148/0x170 > > Signed-off-by: Tobias Klausmann > --- > drivers/net/wireless/ath/ath9k/xmit.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/net/wireless/ath/ath9k/xmit.c b/drivers/net/wireless/ath/ath9k/xmit.c > index 52bfbb988611..857d5ae09a1d 100644 > --- a/drivers/net/wireless/ath/ath9k/xmit.c > +++ b/drivers/net/wireless/ath/ath9k/xmit.c > @@ -2787,6 +2787,7 @@ void ath_tx_edma_tasklet(struct ath_softc *sc) > fifo_list = &txq->txq_fifo[txq->txq_tailidx]; > if (list_empty(fifo_list)) { > ath_txq_unlock(sc, txq); > + rcu_read_unlock(); Technically this is fine as well, but I'd prefer a fix where you replace the 'return' with 'break', thus avoiding the duplication of rcu_read_unlock() Thanks, - Felix