ALSA: pcm: Fix refcount_inc() on zero usage (0e279dce) · Commits · 戴 / test

The recent rewrite of PCM link lock management introduced the refcount in snd_pcm_group object, managed by the kernel refcount_t API. This caused unexpected kernel warnings when the kernel is built with CONFIG_REFCOUNT_FULL=y. As the warning line indicates, the problem is obviously that we start with refcount=0 and do refcount_inc() for adding each PCM link, while refcount_t API doesn't like refcount_inc() performed on zero. For adapting the proper refcount_t usage, this patch changes the logic slightly: - The initial refcount is 1, assuming the single list entry - The refcount is incremented / decremented at each PCM link addition and deletion - ... which allows us concentrating only on the refcount as a release condition Fixes: ("ALSA: pcm: More fine-grained PCM link locking") BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=204221 Reported-and-tested-by:

Duncan Overbruck <kernel@duncano.de> Cc: <stable@vger.kernel.org> Signed-off-by:

Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -77,7 +77,7 @@ void snd_pcm_group_init(struct snd_pcm_group *group)
		spin_lock_init(&group->lock);
		mutex_init(&group->mutex);
		INIT_LIST_HEAD(&group->substreams);
		refcount_set(&group->refs, 0);
		refcount_set(&group->refs, 1);
		}

		/* define group lock helpers */
		@@ -1096,8 +1096,7 @@ static void snd_pcm_group_unref(struct snd_pcm_group *group,

		if (!group)
		return;
		do_free = refcount_dec_and_test(&group->refs) &&
		list_empty(&group->substreams);
		do_free = refcount_dec_and_test(&group->refs);
		snd_pcm_group_unlock(group, substream->pcm->nonatomic);
		if (do_free)
		kfree(group);
		@@ -2020,6 +2019,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
		snd_pcm_group_lock_irq(target_group, nonatomic);
		snd_pcm_stream_lock(substream1);
		snd_pcm_group_assign(substream1, target_group);
		refcount_inc(&target_group->refs);
		snd_pcm_stream_unlock(substream1);
		snd_pcm_group_unlock_irq(target_group, nonatomic);
		_end:
		@@ -2056,13 +2056,14 @@ static int snd_pcm_unlink(struct snd_pcm_substream *substream)
		snd_pcm_group_lock_irq(group, nonatomic);

		relink_to_local(substream);
		refcount_dec(&group->refs);

		/* detach the last stream, too */
		if (list_is_singular(&group->substreams)) {
		relink_to_local(list_first_entry(&group->substreams,
		struct snd_pcm_substream,
		link_list));
		do_free = !refcount_read(&group->refs);
		do_free = refcount_dec_and_test(&group->refs);
		}

		snd_pcm_group_unlock_irq(group, nonatomic);

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