[alsa-devel] [PATCH, RFC 26/30] oss: dmasound: kill SLEEP() macro to avoid race

[Arnd Bergmann]

The use of interruptible_sleep_on_timeout in the dmasound driver
is questionable and we want to kill off all sleep_on variants.
This replaces the calls with wait_event_interruptible_timeout
where possible, to wait for a particular event instead of blocking
in a racy way. In the sq_write function, the easiest solution is
an open-coded prepare_to_wait loop.

Signed-off-by: Arnd Bergmann <arnd at arndb.de>
Cc: Jaroslav Kysela <perex at perex.cz>
Cc: Takashi Iwai <tiwai at suse.de>
Cc: alsa-devel at alsa-project.org
---
 sound/oss/dmasound/dmasound.h      |  1 -
 sound/oss/dmasound/dmasound_core.c | 28 +++++++++++++++++++---------
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/sound/oss/dmasound/dmasound.h b/sound/oss/dmasound/dmasound.h
index 1308d8d..01019f0 100644
--- a/sound/oss/dmasound/dmasound.h
+++ b/sound/oss/dmasound/dmasound.h
@@ -239,7 +239,6 @@ struct sound_queue {
     int busy, syncing, xruns, died;
 };
 
-#define SLEEP(queue)		interruptible_sleep_on_timeout(&queue, HZ)
 #define WAKE_UP(queue)		(wake_up_interruptible(&queue))
 
 extern struct sound_queue dmasound_write_sq;
diff --git a/sound/oss/dmasound/dmasound_core.c b/sound/oss/dmasound/dmasound_core.c
index bac43b5..f4ee85a 100644
--- a/sound/oss/dmasound/dmasound_core.c
+++ b/sound/oss/dmasound/dmasound_core.c
@@ -619,15 +619,27 @@ static ssize_t sq_write(struct file *file, const char __user *src, size_t uLeft,
 	}
 
 	while (uLeft) {
+		DEFINE_WAIT(wait);
+
 		while (write_sq.count >= write_sq.max_active) {
+			prepare_to_wait(&write_sq.action_queue, &wait, TASK_INTERRUPTIBLE);
 			sq_play();
-			if (write_sq.non_blocking)
+			if (write_sq.non_blocking) {
+				finish_wait(&write_sq.action_queue, &wait);
 				return uWritten > 0 ? uWritten : -EAGAIN;
-			SLEEP(write_sq.action_queue);
-			if (signal_pending(current))
+			}
+			if (write_sq.count < write_sq.max_active)
+				break;
+
+			schedule_timeout(HZ);
+			if (signal_pending(current)) {
+				finish_wait(&write_sq.action_queue, &wait);
 				return uWritten > 0 ? uWritten : -EINTR;
+			}
 		}
 
+		finish_wait(&write_sq.action_queue, &wait);
+
 		/* Here, we can avoid disabling the interrupt by first
 		 * copying and translating the data, and then updating
 		 * the write_sq variables. Until this is done, the interrupt
@@ -707,11 +719,8 @@ static int sq_open2(struct sound_queue *sq, struct file *file, fmode_t mode,
 			if (file->f_flags & O_NONBLOCK)
 				return rc;
 			rc = -EINTR;
-			while (sq->busy) {
-				SLEEP(sq->open_queue);
-				if (signal_pending(current))
-					return rc;
-			}
+			if (wait_event_interruptible(sq->open_queue, !sq->busy))
+				return rc;
 			rc = 0;
 #else
 			/* OSS manual says we will return EBUSY regardless
@@ -844,7 +853,8 @@ static int sq_fsync(void)
 	sq_play();	/* there may be an incomplete frame waiting */
 
 	while (write_sq.active) {
-		SLEEP(write_sq.sync_queue);
+		wait_event_interruptible_timeout(write_sq.sync_queue,
+						 !write_sq.active, HZ);
 		if (signal_pending(current)) {
 			/* While waiting for audio output to drain, an
 			 * interrupt occurred.  Stop audio output immediately
-- 
1.8.3.2