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2023-12-09 b22da3d8526a935aa31e086e63f60ff3246cb61c

 kernel/sound/core/misc.c
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@@ -1,22 +1,7 @@
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+// SPDX-License-Identifier: GPL-2.0-or-later
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 /*
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  *  Misc and compatibility things
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  *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
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- *
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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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  */
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6
 
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 #include <linux/init.h>
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@@ -25,6 +10,7 @@
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 #include <linux/time.h>
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 #include <linux/slab.h>
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 #include <linux/ioport.h>
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+#include <linux/fs.h>
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 #include <sound/core.h>
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 #ifdef CONFIG_SND_DEBUG
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@@ -160,3 +146,96 @@
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 }
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 EXPORT_SYMBOL(snd_pci_quirk_lookup);
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 #endif
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+
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+/*
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+ * Deferred async signal helpers
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+ *
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+ * Below are a few helper functions to wrap the async signal handling
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+ * in the deferred work.  The main purpose is to avoid the messy deadlock
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+ * around tasklist_lock and co at the kill_fasync() invocation.
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+ * fasync_helper() and kill_fasync() are replaced with snd_fasync_helper()
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+ * and snd_kill_fasync(), respectively.  In addition, snd_fasync_free() has
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+ * to be called at releasing the relevant file object.
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+ */
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+struct snd_fasync {
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+	struct fasync_struct *fasync;
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+	int signal;
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+	int poll;
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+	int on;
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+	struct list_head list;
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+};
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+
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+static DEFINE_SPINLOCK(snd_fasync_lock);
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+static LIST_HEAD(snd_fasync_list);
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+
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+static void snd_fasync_work_fn(struct work_struct *work)
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+{
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+	struct snd_fasync *fasync;
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+
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+	spin_lock_irq(&snd_fasync_lock);
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+	while (!list_empty(&snd_fasync_list)) {
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+		fasync = list_first_entry(&snd_fasync_list, struct snd_fasync, list);
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+		list_del_init(&fasync->list);
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+		spin_unlock_irq(&snd_fasync_lock);
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+		if (fasync->on)
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+			kill_fasync(&fasync->fasync, fasync->signal, fasync->poll);
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+		spin_lock_irq(&snd_fasync_lock);
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+	}
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+	spin_unlock_irq(&snd_fasync_lock);
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+}
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+
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+static DECLARE_WORK(snd_fasync_work, snd_fasync_work_fn);
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+
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+int snd_fasync_helper(int fd, struct file *file, int on,
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+		      struct snd_fasync **fasyncp)
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+{
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+	struct snd_fasync *fasync = NULL;
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+
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+	if (on) {
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+		fasync = kzalloc(sizeof(*fasync), GFP_KERNEL);
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+		if (!fasync)
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+			return -ENOMEM;
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+		INIT_LIST_HEAD(&fasync->list);
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+	}
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+
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+	spin_lock_irq(&snd_fasync_lock);
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+	if (*fasyncp) {
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+		kfree(fasync);
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+		fasync = *fasyncp;
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+	} else {
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+		if (!fasync) {
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+			spin_unlock_irq(&snd_fasync_lock);
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+			return 0;
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+		}
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+		*fasyncp = fasync;
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+	}
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+	fasync->on = on;
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+	spin_unlock_irq(&snd_fasync_lock);
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+	return fasync_helper(fd, file, on, &fasync->fasync);
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+}
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+EXPORT_SYMBOL_GPL(snd_fasync_helper);
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+
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+void snd_kill_fasync(struct snd_fasync *fasync, int signal, int poll)
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+{
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+	unsigned long flags;
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+
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+	if (!fasync || !fasync->on)
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+		return;
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+	spin_lock_irqsave(&snd_fasync_lock, flags);
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+	fasync->signal = signal;
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+	fasync->poll = poll;
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+	list_move(&fasync->list, &snd_fasync_list);
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+	schedule_work(&snd_fasync_work);
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+	spin_unlock_irqrestore(&snd_fasync_lock, flags);
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+}
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+EXPORT_SYMBOL_GPL(snd_kill_fasync);
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+
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+void snd_fasync_free(struct snd_fasync *fasync)
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+{
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+	if (!fasync)
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+		return;
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+	fasync->on = 0;
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+	flush_work(&snd_fasync_work);
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+	kfree(fasync);
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+}
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+EXPORT_SYMBOL_GPL(snd_fasync_free);