Return-path: Received: from mail-qy0-f181.google.com ([209.85.216.181]:40273 "EHLO mail-qy0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753367Ab1H2OJs convert rfc822-to-8bit (ORCPT ); Mon, 29 Aug 2011 10:09:48 -0400 Received: by qyk34 with SMTP id 34so3772006qyk.19 for ; Mon, 29 Aug 2011 07:09:47 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1314236064-6339-1-git-send-email-thomas@cozybit.com> <20110826142210.GE2579@tuxdriver.com> Date: Mon, 29 Aug 2011 10:09:47 -0400 Message-ID: (sfid-20110829_160954_940058_F66C44BD) Subject: Re: [PATCH] ath5k: Invoke irqsafe version of ieee80211_tx_status() to avoid deadlock From: Bob Copeland To: Thomas Pedersen Cc: "John W. Linville" , linux-wireless@vger.kernel.org, jirislaby@gmail.com, mickflemm@gmail.com, lrodriguez@atheros.com, Javier Cardona Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Sun, Aug 28, 2011 at 10:07 PM, Thomas Pedersen wrote: > On Fri, Aug 26, 2011 at 7:22 AM, John W. Linville > wrote: >> On Wed, Aug 24, 2011 at 06:34:24PM -0700, Thomas Pedersen wrote: >>> From: Javier Cardona >>> >>> This driver reports transmission status to the upper layer >>> (ath5k_tx_frame_completed()) while holding the lock on the transmission >>> queue (txq->lock). ?Under failure conditions, the mesh stack will >>> attempt to send PERR messages to the previous sender of the failed >>> frame. ?When that happens the driver will attempt to re-acquire the >>> txq->lock lock causing a deadlock. ?There are two possible fixes for >>> this, (1) we could defer the transmission of the PERR frame until the >>> lock is released or (2) release the lock before invoking >>> ieee80211_tx_status(). ?The ath9k driver implements the second approach >>> (see ath_tx_complete() in ath9k/xmit.c) as well as the rt2x00 and b43 >>> drivers. ?The iwl driver, on the other hand, avoids this problem by >>> invoking ?ieee80211_tx_status_irqsafe() which effectively defers >>> processing of transmission feedback status. ?This last approach is the >>> least intrusive is implemented here. >>> >>> Reported by Pedro Larbig (ASPj) >>> --- >>> ?drivers/net/wireless/ath/ath5k/base.c | ? ?2 +- >>> ?1 files changed, 1 insertions(+), 1 deletions(-) >> >> Missing Signed-off-by... >> > Yikes. Also, it looks like ieee80211_tx_status() should not be called > from irq context. Will resubmit a v2 with signoff and comment shortly. I don't get the last statement -- ieee80211_tx_status() -> irqsafe was the very change the patch added. It's running in a bottom half though, not a hard irq. -- Bob Copeland %% www.bobcopeland.com