![Kosuke Tatsukawa](/assets/img/avatar_default.png)
snd_seq_oss_readq_put_event() seems to be missing a memory barrier which might cause the waker to not notice the waiter and miss sending a wake_up as in the following figure. snd_seq_oss_readq_put_event snd_seq_oss_readq_wait ------------------------------------------------------------------------ /* wait_event_interruptible_timeout */ /* __wait_event_interruptible_timeout */ /* ___wait_event */ for (;;) { prepare_to_wait_event(&wq, &__wait, state); spin_lock_irqsave(&q->lock, flags); if (waitqueue_active(&q->midi_sleep)) /* The CPU might reorder the test for the waitqueue up here, before prior writes complete */ if ((q->qlen>0 || q->head==q->tail) ... __ret = schedule_timeout(__ret) if (q->qlen >= q->maxlen - 1) { memcpy(&q->q[q->tail], ev, sizeof(*ev)); q->tail = (q->tail + 1) % q->maxlen; q->qlen++; ------------------------------------------------------------------------ There are two other place in sound/core/seq/oss/ which have similar code. The attached patch removes the call to waitqueue_active() leaving just wake_up() behind. This fixes the problem because the call to spin_lock_irqsave() in wake_up() will be an ACQUIRE operation. I found this issue when I was looking through the linux source code for places calling waitqueue_active() before wake_up*(), but without preceding memory barriers, after sending a patch to fix a similar issue in drivers/tty/n_tty.c (Details about the original issue can be found here: https://lkml.org/lkml/2015/9/28/849). Signed-off-by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com> Signed-off-by: Takashi Iwai <tiwai@suse.de>
172 lines
4.1 KiB
C
172 lines
4.1 KiB
C
/*
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* OSS compatible sequencer driver
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*
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* seq_oss_writeq.c - write queue and sync
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*
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* Copyright (C) 1998,99 Takashi Iwai <tiwai@suse.de>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include "seq_oss_writeq.h"
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#include "seq_oss_event.h"
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#include "seq_oss_timer.h"
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#include <sound/seq_oss_legacy.h>
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#include "../seq_lock.h"
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#include "../seq_clientmgr.h"
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#include <linux/wait.h>
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#include <linux/slab.h>
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/*
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* create a write queue record
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*/
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struct seq_oss_writeq *
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snd_seq_oss_writeq_new(struct seq_oss_devinfo *dp, int maxlen)
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{
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struct seq_oss_writeq *q;
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struct snd_seq_client_pool pool;
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if ((q = kzalloc(sizeof(*q), GFP_KERNEL)) == NULL)
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return NULL;
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q->dp = dp;
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q->maxlen = maxlen;
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spin_lock_init(&q->sync_lock);
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q->sync_event_put = 0;
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q->sync_time = 0;
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init_waitqueue_head(&q->sync_sleep);
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memset(&pool, 0, sizeof(pool));
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pool.client = dp->cseq;
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pool.output_pool = maxlen;
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pool.output_room = maxlen / 2;
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snd_seq_oss_control(dp, SNDRV_SEQ_IOCTL_SET_CLIENT_POOL, &pool);
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return q;
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}
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/*
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* delete the write queue
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*/
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void
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snd_seq_oss_writeq_delete(struct seq_oss_writeq *q)
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{
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if (q) {
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snd_seq_oss_writeq_clear(q); /* to be sure */
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kfree(q);
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}
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}
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/*
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* reset the write queue
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*/
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void
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snd_seq_oss_writeq_clear(struct seq_oss_writeq *q)
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{
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struct snd_seq_remove_events reset;
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memset(&reset, 0, sizeof(reset));
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reset.remove_mode = SNDRV_SEQ_REMOVE_OUTPUT; /* remove all */
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snd_seq_oss_control(q->dp, SNDRV_SEQ_IOCTL_REMOVE_EVENTS, &reset);
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/* wake up sleepers if any */
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snd_seq_oss_writeq_wakeup(q, 0);
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}
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/*
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* wait until the write buffer has enough room
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*/
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int
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snd_seq_oss_writeq_sync(struct seq_oss_writeq *q)
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{
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struct seq_oss_devinfo *dp = q->dp;
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abstime_t time;
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time = snd_seq_oss_timer_cur_tick(dp->timer);
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if (q->sync_time >= time)
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return 0; /* already finished */
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if (! q->sync_event_put) {
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struct snd_seq_event ev;
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union evrec *rec;
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/* put echoback event */
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memset(&ev, 0, sizeof(ev));
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ev.flags = 0;
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ev.type = SNDRV_SEQ_EVENT_ECHO;
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ev.time.tick = time;
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/* echo back to itself */
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snd_seq_oss_fill_addr(dp, &ev, dp->addr.client, dp->addr.port);
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rec = (union evrec *)&ev.data;
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rec->t.code = SEQ_SYNCTIMER;
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rec->t.time = time;
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q->sync_event_put = 1;
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snd_seq_kernel_client_enqueue_blocking(dp->cseq, &ev, NULL, 0, 0);
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}
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wait_event_interruptible_timeout(q->sync_sleep, ! q->sync_event_put, HZ);
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if (signal_pending(current))
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/* interrupted - return 0 to finish sync */
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q->sync_event_put = 0;
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if (! q->sync_event_put || q->sync_time >= time)
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return 0;
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return 1;
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}
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/*
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* wake up sync - echo event was catched
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*/
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void
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snd_seq_oss_writeq_wakeup(struct seq_oss_writeq *q, abstime_t time)
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{
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unsigned long flags;
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spin_lock_irqsave(&q->sync_lock, flags);
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q->sync_time = time;
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q->sync_event_put = 0;
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wake_up(&q->sync_sleep);
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spin_unlock_irqrestore(&q->sync_lock, flags);
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}
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/*
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* return the unused pool size
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*/
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int
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snd_seq_oss_writeq_get_free_size(struct seq_oss_writeq *q)
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{
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struct snd_seq_client_pool pool;
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pool.client = q->dp->cseq;
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snd_seq_oss_control(q->dp, SNDRV_SEQ_IOCTL_GET_CLIENT_POOL, &pool);
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return pool.output_free;
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}
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/*
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* set output threshold size from ioctl
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*/
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void
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snd_seq_oss_writeq_set_output(struct seq_oss_writeq *q, int val)
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{
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struct snd_seq_client_pool pool;
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pool.client = q->dp->cseq;
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snd_seq_oss_control(q->dp, SNDRV_SEQ_IOCTL_GET_CLIENT_POOL, &pool);
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pool.output_room = val;
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snd_seq_oss_control(q->dp, SNDRV_SEQ_IOCTL_SET_CLIENT_POOL, &pool);
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}
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