linux-kernel - [PATCH] avr32: fix deadlock when reading clock list in debugfs

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Message-ID: <20100912162628.GA15423@siv>
Date:	Sun, 12 Sep 2010 18:26:28 +0200
From:	Ole Henrik Jahren <olehenja@...mni.ntnu.no>
To:	kernel@...32linux.org
Cc:	Haavard Skinnemoen <hskinnemoen@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] avr32: fix deadlock when reading clock list in debugfs

From: Ole Henrik Jahren <olehenja@...mni.ntnu.no>

clk_show() already has clk_list_lock. Make a version of clk_get(),
clk_get_locked(), that does not attempt to take the lock a second time.

Signed-off-by: Ole Henrik Jahren <olehenja@...mni.ntnu.no>
Cc: Haavard Skinnemoen <hskinnemoen@...el.com>
---
 arch/avr32/mach-at32ap/clock.c |   27 ++++++++++++++++++++-------
 1 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/arch/avr32/mach-at32ap/clock.c b/arch/avr32/mach-at32ap/clock.c
index 442f08c..3951993 100644
--- a/arch/avr32/mach-at32ap/clock.c
+++ b/arch/avr32/mach-at32ap/clock.c
@@ -35,22 +35,30 @@ void at32_clk_register(struct clk *clk)
 	spin_unlock(&clk_list_lock);
 }
 
-struct clk *clk_get(struct device *dev, const char *id)
+static struct clk *__clk_get(struct device *dev, const char *id, int locked)
 {
 	struct clk *clk;
 
-	spin_lock(&clk_list_lock);
+	if (!locked)
+		spin_lock(&clk_list_lock);
 
 	list_for_each_entry(clk, &at32_clock_list, list) {
 		if (clk->dev == dev && strcmp(id, clk->name) == 0) {
-			spin_unlock(&clk_list_lock);
+			if (!locked)
+				spin_unlock(&clk_list_lock);
 			return clk;
 		}
 	}
 
-	spin_unlock(&clk_list_lock);
+	if (!locked)
+		spin_unlock(&clk_list_lock);
 	return ERR_PTR(-ENOENT);
 }
+
+struct clk *clk_get(struct device *dev, const char *id)
+{
+	return __clk_get(dev, id, 0);
+}
 EXPORT_SYMBOL(clk_get);
 
 void clk_put(struct clk *clk)
@@ -227,6 +235,11 @@ dump_clock(struct clk *parent, struct clkinf *r)
 	r->nest = nest;
 }
 
+static struct clk *clk_get_locked(struct device *dev, const char *id)
+{
+	return __clk_get(dev, id, 1);
+}
+
 static int clk_show(struct seq_file *s, void *unused)
 {
 	struct clkinf	r;
@@ -257,15 +270,15 @@ static int clk_show(struct seq_file *s, void *unused)
 	spin_lock(&clk_list_lock);
 
 	/* show clock tree as derived from the three oscillators */
-	clk = clk_get(NULL, "osc32k");
+	clk = clk_get_locked(NULL, "osc32k");
 	dump_clock(clk, &r);
 	clk_put(clk);
 
-	clk = clk_get(NULL, "osc0");
+	clk = clk_get_locked(NULL, "osc0");
 	dump_clock(clk, &r);
 	clk_put(clk);
 
-	clk = clk_get(NULL, "osc1");
+	clk = clk_get_locked(NULL, "osc1");
 	dump_clock(clk, &r);
 	clk_put(clk);
 
-- 
1.7.2.2

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