From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:45270 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730577AbeLKP43 (ORCPT ); Tue, 11 Dec 2018 10:56:29 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Chanho Min , Takashi Iwai Subject: [PATCH 4.19 064/118] ALSA: pcm: Call snd_pcm_unlink() conditionally at closing Date: Tue, 11 Dec 2018 16:41:23 +0100 Message-Id: <20181211151646.822488652@linuxfoundation.org> In-Reply-To: <20181211151644.216668863@linuxfoundation.org> References: <20181211151644.216668863@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai commit b51abed8355e5556886623b2772fa6b7598d2282 upstream. Currently the PCM core calls snd_pcm_unlink() always unconditionally at closing a stream. However, since snd_pcm_unlink() invokes the global rwsem down, the lock can be easily contended. More badly, when a thread runs in a high priority RT-FIFO, it may stall at spinning. Basically the call of snd_pcm_unlink() is required only for the linked streams that are already rare occasion. For normal use cases, this code path is fairly superfluous. As an optimization (and also as a workaround for the RT problem above in normal situations without linked streams), this patch adds a check before calling snd_pcm_unlink() and calls it only when needed. Reported-by: Chanho Min Cc: Signed-off-by: Takashi Iwai Signed-off-by: Greg Kroah-Hartman --- sound/core/pcm_native.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -2370,7 +2370,8 @@ int snd_pcm_hw_constraints_complete(stru static void pcm_release_private(struct snd_pcm_substream *substream) { - snd_pcm_unlink(substream); + if (snd_pcm_stream_linked(substream)) + snd_pcm_unlink(substream); } void snd_pcm_release_substream(struct snd_pcm_substream *substream)