linux-kernel - [PATCH, RFC 25/30] oss: vwsnd: avoid interruptible_sleep

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Date:	Thu,  2 Jan 2014 13:07:49 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-kernel@...r.kernel.org
Cc:	Arnd Bergmann <arnd@...db.de>, Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.de>, alsa-devel@...a-project.org
Subject: [PATCH, RFC 25/30] oss: vwsnd: avoid interruptible_sleep_on

Interruptible_sleep_on is racy and we want to remove it. This replaces
the use in the vwsnd driver with an open-coded prepare_to_wait
loop that fixes the race between concurrent open() and close() calls,
and also drops the global mutex while waiting here, which restores
the original behavior that was changed during the BKL removal.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Cc: Jaroslav Kysela <perex@...ex.cz>
Cc: Takashi Iwai <tiwai@...e.de>
Cc: alsa-devel@...a-project.org
---
 sound/oss/vwsnd.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/sound/oss/vwsnd.c b/sound/oss/vwsnd.c
index 4bbcc0f..a077e9c 100644
--- a/sound/oss/vwsnd.c
+++ b/sound/oss/vwsnd.c
@@ -2921,6 +2921,7 @@ static int vwsnd_audio_open(struct inode *inode, struct file *file)
 	vwsnd_dev_t *devc;
 	int minor = iminor(inode);
 	int sw_samplefmt;
+	DEFINE_WAIT(wait);
 
 	DBGE("(inode=0x%p, file=0x%p)\n", inode, file);
 
@@ -2937,21 +2938,26 @@ static int vwsnd_audio_open(struct inode *inode, struct file *file)
 	}
 
 	mutex_lock(&devc->open_mutex);
-	while (devc->open_mode & file->f_mode) {
+	while (1) {
+		prepare_to_wait(&devc->open_wait, &wait, TASK_INTERRUPTIBLE);
+		if (!(devc->open_mode & file->f_mode))
+			break;
+
 		mutex_unlock(&devc->open_mutex);
+		mutex_unlock(&vwsnd_mutex);
 		if (file->f_flags & O_NONBLOCK) {
 			DEC_USE_COUNT;
-			mutex_unlock(&vwsnd_mutex);
 			return -EBUSY;
 		}
-		interruptible_sleep_on(&devc->open_wait);
+		schedule();
 		if (signal_pending(current)) {
 			DEC_USE_COUNT;
-			mutex_unlock(&vwsnd_mutex);
 			return -ERESTARTSYS;
 		}
+		mutex_lock(&vwsnd_mutex);
 		mutex_lock(&devc->open_mutex);
 	}
+	finish_wait(&devc->open_wait, &wait);
 	devc->open_mode |= file->f_mode & (FMODE_READ | FMODE_WRITE);
 	mutex_unlock(&devc->open_mutex);
 
-- 
1.8.3.2

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