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

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

[Ole Henrik Jahren]

From: Ole Henrik Jahren <olehenja@alumni.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@alumni.ntnu.no>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.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

Re: [PATCH] avr32: fix deadlock when reading clock list in debugfs

[Hans-Christian Egtvedt]

On Sun, 2011-03-06 at 20:42 +0100, Ole Henrik Jahren wrote: 
> When writing out /sys/kernel/debug/at32ap_clk, clock list lock is being
> held while clk_get() is called. clk_get() attempts to take the same
> lock, which results in deadlock. Introduce and call lock free version,
> __clk_get(), instead.
> 
> Signed-off-by: Ole Henrik Jahren <olehenja@alumni.ntnu.no>
> Cc: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>

Thanks for this fix, added to the AVR32 tree.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>

<snipp patch>

-- 
Hans-Christian Egtvedt

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

[Ole Henrik Jahren]

When writing out /sys/kernel/debug/at32ap_clk, clock list lock is being
held while clk_get() is called. clk_get() attempts to take the same
lock, which results in deadlock. Introduce and call lock free version,
__clk_get(), instead.

Signed-off-by: Ole Henrik Jahren <olehenja@alumni.ntnu.no>
Cc: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
---
 arch/avr32/mach-at32ap/clock.c |   24 ++++++++++++++++--------
 1 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/arch/avr32/mach-at32ap/clock.c b/arch/avr32/mach-at32ap/clock.c
index 442f08c..86925fd 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)
 {
 	struct clk *clk;
 
-	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);
 			return clk;
 		}
 	}
 
-	spin_unlock(&clk_list_lock);
 	return ERR_PTR(-ENOENT);
 }
+
+struct clk *clk_get(struct device *dev, const char *id)
+{
+	struct clk *clk;
+
+	spin_lock(&clk_list_lock);
+	clk = __clk_get(dev, id);
+	spin_unlock(&clk_list_lock);
+
+	return clk;
+}
+
 EXPORT_SYMBOL(clk_get);
 
 void clk_put(struct clk *clk)
@@ -257,15 +265,15 @@ 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(NULL, "osc32k");
 	dump_clock(clk, &r);
 	clk_put(clk);
 
-	clk = clk_get(NULL, "osc0");
+	clk = __clk_get(NULL, "osc0");
 	dump_clock(clk, &r);
 	clk_put(clk);
 
-	clk = clk_get(NULL, "osc1");
+	clk = __clk_get(NULL, "osc1");
 	dump_clock(clk, &r);
 	clk_put(clk);
 
-- 
1.7.4