From patchwork Mon Nov 26 05:36:37 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chanho Min X-Patchwork-Id: 10697597 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 766A517FE for ; Mon, 26 Nov 2018 05:37:00 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 5C76A297F0 for ; Mon, 26 Nov 2018 05:37:00 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 4A5B929872; Mon, 26 Nov 2018 05:37:00 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.1 Received: from alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 09813297F0 for ; Mon, 26 Nov 2018 05:36:58 +0000 (UTC) Received: from alsa0.perex.cz (localhost [127.0.0.1]) by alsa0.perex.cz (Postfix) with ESMTP id 3BBC42679B4; Mon, 26 Nov 2018 06:36:57 +0100 (CET) X-Original-To: alsa-devel@alsa-project.org Delivered-To: alsa-devel@alsa-project.org Received: by alsa0.perex.cz (Postfix, from userid 1000) id 167F6267A8E; Mon, 26 Nov 2018 06:36:55 +0100 (CET) Received: from lgeamrelo11.lge.com (lgeamrelo12.lge.com [156.147.23.52]) by alsa0.perex.cz (Postfix) with ESMTP id 939992679A7 for ; Mon, 26 Nov 2018 06:36:50 +0100 (CET) Received: from unknown (HELO lgeamrelo02.lge.com) (156.147.1.126) by 156.147.23.52 with ESMTP; 26 Nov 2018 14:36:48 +0900 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: chanho.min@lge.com Received: from unknown (HELO kernel.lge.com) (165.186.175.97) by 156.147.1.126 with ESMTP; 26 Nov 2018 14:36:48 +0900 X-Original-SENDERIP: 165.186.175.97 X-Original-MAILFROM: chanho.min@lge.com From: Chanho Min To: Jaroslav Kysela , Takashi Iwai , Vinod Koul , Daniel Mentz Date: Mon, 26 Nov 2018 14:36:37 +0900 Message-Id: <1543210597-6717-1-git-send-email-chanho.min@lge.com> X-Mailer: git-send-email 2.1.4 Cc: alsa-devel@alsa-project.org, Jaehyun Kim , Jongsung Kim , Chanho Min , linux-kernel@vger.kernel.org, Hyonwoo Park , Wonmin Jung , Seungho Park Subject: [alsa-devel] [PATCH] ALSA: pcm: Fix starvation on down_write_nonblock() X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org X-Virus-Scanned: ClamAV using ClamSMTP Commit 67ec1072b053 ("ALSA: pcm: Fix rwsem deadlock for non-atomic PCM stream") fixes deadlock for non-atomic PCM stream. But, This patch causes antother stuck. If writer is RT thread and reader is a normal thread, the reader thread will be difficult to get scheduled. It may not give chance to release readlocks and writer gets stuck for a long time if they are pinned to single cpu. The deadlock described in the previous commit is because the linux rwsem queues like a FIFO. So, we might need non-FIFO writelock, not non-block one. My suggestion is that the writer gives reader a chance to be scheduled by using the minimum msleep() instaed of spinning without blocking by writer. Also, The *_nonblock may be changed to *_nonfifo appropriately to this concept. In terms of performance, when trylock is failed, this minimum periodic msleep will have the same performance as the tick-based schedule()/wake_up_q(). Suggested-by: Wonmin Jung Signed-off-by: Chanho Min Reported-by: Chanho Min Signed-off-by: Takashi Iwai --- sound/core/pcm_native.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 66c90f4..bdca0e1 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -36,6 +36,7 @@ #include #include #include +#include #include "pcm_local.h" @@ -91,12 +92,12 @@ static DECLARE_RWSEM(snd_pcm_link_rwsem); * and this may lead to a deadlock when the code path takes read sem * twice (e.g. one in snd_pcm_action_nonatomic() and another in * snd_pcm_stream_lock()). As a (suboptimal) workaround, let writer to - * spin until it gets the lock. + * sleep until all the readers are completed without blocking by writer. */ -static inline void down_write_nonblock(struct rw_semaphore *lock) +static inline void down_write_nonfifo(struct rw_semaphore *lock) { while (!down_write_trylock(lock)) - cond_resched(); + msleep(1); } #define PCM_LOCK_DEFAULT 0 @@ -1967,7 +1968,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd) res = -ENOMEM; goto _nolock; } - down_write_nonblock(&snd_pcm_link_rwsem); + down_write_nonfifo(&snd_pcm_link_rwsem); write_lock_irq(&snd_pcm_link_rwlock); if (substream->runtime->status->state == SNDRV_PCM_STATE_OPEN || substream->runtime->status->state != substream1->runtime->status->state || @@ -2014,7 +2015,7 @@ static int snd_pcm_unlink(struct snd_pcm_substream *substream) struct snd_pcm_substream *s; int res = 0; - down_write_nonblock(&snd_pcm_link_rwsem); + down_write_nonfifo(&snd_pcm_link_rwsem); write_lock_irq(&snd_pcm_link_rwlock); if (!snd_pcm_stream_linked(substream)) { res = -EALREADY;