2011-03-06 19:46:27

by Ole Henrik Jahren

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

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 <[email protected]>
Cc: Hans-Christian Egtvedt <[email protected]>
---
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

2011-04-13 13:17:53

by Hans-Christian Egtvedt

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

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 <[email protected]>
> Cc: Hans-Christian Egtvedt <[email protected]>

Thanks for this fix, added to the AVR32 tree.

Signed-off-by: Hans-Christian Egtvedt <[email protected]>

<snipp patch>

--
Hans-Christian Egtvedt