Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966477AbcDLVaw (ORCPT ); Tue, 12 Apr 2016 17:30:52 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:50770 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966427AbcDLUxl (ORCPT ); Tue, 12 Apr 2016 16:53:41 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Takashi Iwai , Kamal Mostafa Subject: [PATCH 4.2.y-ckt 32/70] ALSA: timer: Use mod_timer() for rearming the system timer Date: Tue, 12 Apr 2016 13:52:17 -0700 Message-Id: <1460494375-30070-33-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1460494375-30070-1-git-send-email-kamal@canonical.com> References: <1460494375-30070-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 4.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2129 Lines: 58 4.2.8-ckt8 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Takashi Iwai commit 4a07083ed613644c96c34a7dd2853dc5d7c70902 upstream. ALSA system timer backend stops the timer via del_timer() without sync and leaves del_timer_sync() at the close instead. This is because of the restriction by the design of ALSA timer: namely, the stop callback may be called from the timer handler, and calling the sync shall lead to a hangup. However, this also triggers a kernel BUG() when the timer is rearmed immediately after stopping without sync: kernel BUG at kernel/time/timer.c:966! Call Trace: [] snd_timer_s_start+0x13e/0x1a0 [] snd_timer_interrupt+0x504/0xec0 [] ? debug_check_no_locks_freed+0x290/0x290 [] snd_timer_s_function+0xb4/0x120 [] call_timer_fn+0x162/0x520 [] ? call_timer_fn+0xcd/0x520 [] ? snd_timer_interrupt+0xec0/0xec0 .... It's the place where add_timer() checks the pending timer. It's clear that this may happen after the immediate restart without sync in our cases. So, the workaround here is just to use mod_timer() instead of add_timer(). This looks like a band-aid fix, but it's a right move, as snd_timer_interrupt() takes care of the continuous rearm of timer. Reported-by: Jiri Slaby Signed-off-by: Takashi Iwai Signed-off-by: Kamal Mostafa --- sound/core/timer.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/sound/core/timer.c b/sound/core/timer.c index f24c9fc..b982d1b 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1051,8 +1051,8 @@ static int snd_timer_s_start(struct snd_timer * timer) njiff += timer->sticks - priv->correction; priv->correction = 0; } - priv->last_expires = priv->tlist.expires = njiff; - add_timer(&priv->tlist); + priv->last_expires = njiff; + mod_timer(&priv->tlist, njiff); return 0; } -- 2.7.4