[PATCH 3.2 36/79] blktrace: fix unlocked access to init/start-stop/teardown

[Ben Hutchings <ben@decadent.org.uk>]

3.2.99-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jens Axboe <axboe@kernel.dk>

commit 1f2cac107c591c24b60b115d6050adc213d10fc0 upstream.

sg.c calls into the blktrace functions without holding the proper queue
mutex for doing setup, start/stop, or teardown.

Add internal unlocked variants, and export the ones that do the proper
locking.

Fixes: 6da127ad0918 ("blktrace: Add blktrace ioctls to SCSI generic devices")
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 kernel/trace/blktrace.c | 58 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 48 insertions(+), 10 deletions(-)

--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -296,7 +296,7 @@ static void blk_trace_cleanup(struct blk
 		blk_unregister_tracepoints();
 }
 
-int blk_trace_remove(struct request_queue *q)
+static int __blk_trace_remove(struct request_queue *q)
 {
 	struct blk_trace *bt;
 
@@ -309,6 +309,17 @@ int blk_trace_remove(struct request_queu
 
 	return 0;
 }
+
+int blk_trace_remove(struct request_queue *q)
+{
+	int ret;
+
+	mutex_lock(&q->blk_trace_mutex);
+	ret = __blk_trace_remove(q);
+	mutex_unlock(&q->blk_trace_mutex);
+
+	return ret;
+}
 EXPORT_SYMBOL_GPL(blk_trace_remove);
 
 static int blk_dropped_open(struct inode *inode, struct file *filp)
@@ -538,9 +549,8 @@ err:
 	return ret;
 }
 
-int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
-		    struct block_device *bdev,
-		    char __user *arg)
+static int __blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
+			     struct block_device *bdev, char __user *arg)
 {
 	struct blk_user_trace_setup buts;
 	int ret;
@@ -559,6 +569,19 @@ int blk_trace_setup(struct request_queue
 	}
 	return 0;
 }
+
+int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
+		    struct block_device *bdev,
+		    char __user *arg)
+{
+	int ret;
+
+	mutex_lock(&q->blk_trace_mutex);
+	ret = __blk_trace_setup(q, name, dev, bdev, arg);
+	mutex_unlock(&q->blk_trace_mutex);
+
+	return ret;
+}
 EXPORT_SYMBOL_GPL(blk_trace_setup);
 
 #if defined(CONFIG_COMPAT) && defined(CONFIG_X86_64)
@@ -596,7 +619,7 @@ static int compat_blk_trace_setup(struct
 }
 #endif
 
-int blk_trace_startstop(struct request_queue *q, int start)
+static int __blk_trace_startstop(struct request_queue *q, int start)
 {
 	int ret;
 	struct blk_trace *bt = q->blk_trace;
@@ -629,6 +652,17 @@ int blk_trace_startstop(struct request_q
 
 	return ret;
 }
+
+int blk_trace_startstop(struct request_queue *q, int start)
+{
+	int ret;
+
+	mutex_lock(&q->blk_trace_mutex);
+	ret = __blk_trace_startstop(q, start);
+	mutex_unlock(&q->blk_trace_mutex);
+
+	return ret;
+}
 EXPORT_SYMBOL_GPL(blk_trace_startstop);
 
 /*
@@ -659,7 +693,7 @@ int blk_trace_ioctl(struct block_device
 	switch (cmd) {
 	case BLKTRACESETUP:
 		bdevname(bdev, b);
-		ret = blk_trace_setup(q, b, bdev->bd_dev, bdev, arg);
+		ret = __blk_trace_setup(q, b, bdev->bd_dev, bdev, arg);
 		break;
 #if defined(CONFIG_COMPAT) && defined(CONFIG_X86_64)
 	case BLKTRACESETUP32:
@@ -670,10 +704,10 @@ int blk_trace_ioctl(struct block_device
 	case BLKTRACESTART:
 		start = 1;
 	case BLKTRACESTOP:
-		ret = blk_trace_startstop(q, start);
+		ret = __blk_trace_startstop(q, start);
 		break;
 	case BLKTRACETEARDOWN:
-		ret = blk_trace_remove(q);
+		ret = __blk_trace_remove(q);
 		break;
 	default:
 		ret = -ENOTTY;
@@ -691,10 +725,14 @@ int blk_trace_ioctl(struct block_device
  **/
 void blk_trace_shutdown(struct request_queue *q)
 {
+	mutex_lock(&q->blk_trace_mutex);
+
 	if (q->blk_trace) {
-		blk_trace_startstop(q, 0);
-		blk_trace_remove(q);
+		__blk_trace_startstop(q, 0);
+		__blk_trace_remove(q);
 	}
+
+	mutex_unlock(&q->blk_trace_mutex);
 }
 
 /*