Return-path: Received: from atlantic540.startdedicated.de ([188.138.9.77]:35475 "EHLO atlantic540.startdedicated.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752696AbcHRNi1 (ORCPT ); Thu, 18 Aug 2016 09:38:27 -0400 From: Daniel Wagner To: Kalle Valo Cc: Christian Lamparter , "Luis R . Rodriguez" , ath10k@lists.infradead.org, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Wagner Subject: [PATCH 1/2] carl9170: Fix wrong completion usage Date: Thu, 18 Aug 2016 15:12:05 +0200 Message-Id: <1471525926-20384-2-git-send-email-wagi@monom.org> (sfid-20160818_153837_116836_090081BF) In-Reply-To: <1471525926-20384-1-git-send-email-wagi@monom.org> References: <1471525926-20384-1-git-send-email-wagi@monom.org> Sender: linux-wireless-owner@vger.kernel.org List-ID: From: Daniel Wagner carl9170_usb_stop() is used from several places to flush and cleanup any pending work. The normal pattern is to send a request and wait for the irq handler to call complete(). The completion is not reinitialized during normal operation and as the old comment indicates it is important to keep calls to wait_for_completion_timeout() and complete() balanced. Calling complete_all() brings this equilibirum out of balance and needs to be fixed by a reinit_completion(). But that opens a small race window. It is possible that the sequence of complete_all(), reinit_completion() is faster than the wait_for_completion_timeout() can do its work. The wake up is not lost but the done counter test is after reinit_completion() has been executed. The only reason we don't see carl9170_exec_cmd() hang forever is we use the timeout version of wait_for_copletion(). Let's fix this by reinitializing the completion (that is just setting done counter to 0) just before we send out an request. Now, carl9170_usb_stop() can be sure a complete() call is enough to make progess since there is only one waiter at max. This is a common pattern also seen in various drivers which use completion. Signed-off-by: Daniel Wagner --- drivers/net/wireless/ath/carl9170/usb.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/drivers/net/wireless/ath/carl9170/usb.c b/drivers/net/wireless/ath/carl9170/usb.c index 76842e6..99ab203 100644 --- a/drivers/net/wireless/ath/carl9170/usb.c +++ b/drivers/net/wireless/ath/carl9170/usb.c @@ -670,6 +670,7 @@ int carl9170_exec_cmd(struct ar9170 *ar, const enum carl9170_cmd_oids cmd, ar->readlen = outlen; spin_unlock_bh(&ar->cmd_lock); + reinit_completion(&ar->cmd_wait); err = __carl9170_exec_cmd(ar, &ar->cmd, false); if (!(cmd & CARL9170_CMD_ASYNC_FLAG)) { @@ -778,10 +779,7 @@ void carl9170_usb_stop(struct ar9170 *ar) spin_lock_bh(&ar->cmd_lock); ar->readlen = 0; spin_unlock_bh(&ar->cmd_lock); - complete_all(&ar->cmd_wait); - - /* This is required to prevent an early completion on _start */ - reinit_completion(&ar->cmd_wait); + complete(&ar->cmd_wait); /* * Note: -- 2.7.4