linux-kernel - [PATCH] staging: unisys: visorbus: visorchannel: Refactor locking code to be statically deterministic.

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Message-Id: <1476876643-3708-1-git-send-email-chuckleberryfinn@gmail.com>
Date:   Wed, 19 Oct 2016 12:30:43 +0100
From:   Cathal Mullaney <chuckleberryfinn@...il.com>
To:     david.kershner@...sys.com
Cc:     gregkh@...uxfoundation.org, sparmaintainer@...sys.com,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Cathal Mullaney <chuckleberryfinn@...il.com>
Subject: [PATCH] staging: unisys: visorbus: visorchannel: Refactor locking code to be statically deterministic.

This patch makes locking in visorchannel_signalempty statically deterministic.
As a result this patch fixes the sparse warning:
Context imbalance in 'visorchannel_signalempty' - different lock contexts for basic block.

The logic of the locking code doesn't change but the layout of the original code is "frowned upon"
according to mails on sparse context checking.
Refactoring removes the warning and makes the code more readable.

Signed-off-by: Cathal Mullaney <chuckleberryfinn@...il.com>
---
 drivers/staging/unisys/visorbus/visorchannel.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/drivers/staging/unisys/visorbus/visorchannel.c b/drivers/staging/unisys/visorbus/visorchannel.c
index a1381eb..1eea5d8 100644
--- a/drivers/staging/unisys/visorbus/visorchannel.c
+++ b/drivers/staging/unisys/visorbus/visorchannel.c
@@ -300,22 +300,30 @@ EXPORT_SYMBOL_GPL(visorchannel_signalremove);
  * Return: boolean indicating whether any messages in the designated
  *         channel/queue are present
  */
+
+static bool
+queue_empty(struct visorchannel *channel, u32 queue)
+{
+	struct signal_queue_header sig_hdr;
+
+	if (sig_read_header(channel, queue, &sig_hdr))
+		return true;
+
+	return (sig_hdr.head == sig_hdr.tail);
+}
+
 bool
 visorchannel_signalempty(struct visorchannel *channel, u32 queue)
 {
 	unsigned long flags = 0;
-	struct signal_queue_header sig_hdr;
 	bool rc = false;
 
-	if (channel->needs_lock)
-		spin_lock_irqsave(&channel->remove_lock, flags);
+	if (!channel->needs_lock)
+		return queue_empty(channel, queue);
 
-	if (sig_read_header(channel, queue, &sig_hdr))
-		rc = true;
-	if (sig_hdr.head == sig_hdr.tail)
-		rc = true;
-	if (channel->needs_lock)
-		spin_unlock_irqrestore(&channel->remove_lock, flags);
+	spin_lock_irqsave(&channel->remove_lock, flags);
+	rc = queue_empty(channel, queue);
+	spin_unlock_irqrestore(&channel->remove_lock, flags);
 
 	return rc;
 }
-- 
2.7.4