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audio(4): Membar audit. 

Won't affect anything on x86 because atomic r/m/w operations are
always full sequential consistency barriers, but might potentially
fix problems on, e.g., arm.

Note 1: I'm not clear on why the track lock is a bespoke mutex made
out of an atomic -- why not just mutex(9)?

Note 2: I'm not convinced the audio_mlog_flush synchronization is
correct; what happens if the softint runs on two CPUs at the same
time and swaps mlog_wpage simultaneously?

Note 3: Should maybe use atomic_load/store_relaxed for mlog_full and
mlog_drop, and atomic_inc/dec for mlog_refs.
This commit is contained in:
riastradh 2022-03-14 11:47:33 +00:00
parent cfdc83f9e5
commit 826d03fdc0
1 changed files with 16 additions and 7 deletions
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23
sys/dev/audio/audio.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: audio.c,v 1.113 2021/12/12 13:05:13 andvar Exp $ */
/* $NetBSD: audio.c,v 1.114 2022/03/14 11:47:33 riastradh Exp $ */
/*-
* Copyright (c) 2008 The NetBSD Foundation, Inc.
@ -138,7 +138,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: audio.c,v 1.113 2021/12/12 13:05:13 andvar Exp $");
__KERNEL_RCSID(0, "$NetBSD: audio.c,v 1.114 2022/03/14 11:47:33 riastradh Exp $");
#ifdef _KERNEL_OPT
#include "audio.h"
@ -162,6 +162,7 @@ __KERNEL_RCSID(0, "$NetBSD: audio.c,v 1.113 2021/12/12 13:05:13 andvar Exp $");
#include <sys/kauth.h>
#include <sys/kernel.h>
#include <sys/kmem.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mman.h>
#include <sys/module.h>
@ -272,13 +273,14 @@ audio_mlog_flush(void)
/* Nothing to do if already in use ? */
if (atomic_swap_32(&mlog_inuse, 1) == 1)
return;
membar_enter();
int rpage = mlog_wpage;
mlog_wpage ^= 1;
mlog_buf[mlog_wpage][0] = '\0';
mlog_used = 0;
atomic_swap_32(&mlog_inuse, 0);
atomic_store_reease(&mlog_inuse, 0);
if (mlog_buf[rpage][0] != '\0') {
printf("%s", mlog_buf[rpage]);
@ -308,6 +310,7 @@ audio_mlog_printf(const char *fmt, ...)
mlog_drop++;
return;
}
membar_enter();
va_start(ap, fmt);
len = vsnprintf(
@ -321,7 +324,7 @@ audio_mlog_printf(const char *fmt, ...)
mlog_full++;
}
atomic_swap_32(&mlog_inuse, 0);
atomic_store_release(&mlog_inuse, 0);
if (mlog_sih)
softint_schedule(mlog_sih);
@ -1652,7 +1655,11 @@ audio_track_waitio(struct audio_softc *sc, audio_track_t *track)
static __inline bool
audio_track_lock_tryenter(audio_track_t *track)
{
return (atomic_cas_uint(&track->lock, 0, 1) == 0);
if (atomic_swap_uint(&track->lock, 1) != 0)
return false;
membar_enter();
return true;
}
/*
@ -1661,9 +1668,10 @@ audio_track_lock_tryenter(audio_track_t *track)
static __inline void
audio_track_lock_enter(audio_track_t *track)
{
/* Don't sleep here. */
while (audio_track_lock_tryenter(track) == false)
;
SPINLOCK_BACKOFF_HOOK;
}
/*
@ -1672,7 +1680,8 @@ audio_track_lock_enter(audio_track_t *track)
static __inline void
audio_track_lock_exit(audio_track_t *track)
{
atomic_swap_uint(&track->lock, 0);
atomic_store_release(&track->lock, 0);
}