linux-kernel - Re: applesmc oops in 3.10/3.11

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Message-ID: <20130926063453.GA526@polaris.bitmath.org>
Date:	Thu, 26 Sep 2013 08:34:53 +0200
From:	Henrik Rydberg <rydberg@...omail.se>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Josh Boyer <jwboyer@...oraproject.org>, khali@...ux-fr.org,
	lm-sensors@...sensors.org,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	bugzilla@...orremedies.com
Subject: Re: applesmc oops in 3.10/3.11

> > > This suggests that initialization may be attempted more than once. The key cache
> > > is allocated only once, but the number of keys is read for each attempt.
> > > 
> > > No idea if that can happen, but if the number of keys can increase after
> > > the first initialization attempt you would have an explanation for the crash.
> > 
> > Good idea, and easy enough to test with the patch below.
> > 
> Should we apply this patch even though it may not solve the specific problem ?

Yes, why not - it certainly won't hurt. I am running it right now, so
it is at least run-tested.

> Again, not sure if the key count can change, but the current code is at the very
> least inconsistent, as it keeps reading the key count without updating or
> verifying the cache size.

Yes - I agree that the error state is far-fetched, but it is hard to
see any other logical explanation. There is of course always the
possibility that the problem is somewhere else completely.

Proper patch attached.

Thanks,
Henrik

---

>From dedefba9167913c46e1896ce0624e68ffe95d532 Mon Sep 17 00:00:00 2001
From: Henrik Rydberg <rydberg@...omail.se>
Date: Thu, 26 Sep 2013 08:33:16 +0200
Subject: [PATCH] hwmon: (applesmc) Check key count before proceeding

After reports from Chris and Josh Boyer of a rare crash in applesmc,
Guenter pointed at the initialization problem fixed below. The patch
has not been verified to fix the crash, but should be applied
regardless.

Reported-by: <jwboyer@...oraproject.org>
Suggested-by: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Henrik Rydberg <rydberg@...omail.se>
---
 drivers/hwmon/applesmc.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/applesmc.c b/drivers/hwmon/applesmc.c
index 62c2e32..98814d1 100644
--- a/drivers/hwmon/applesmc.c
+++ b/drivers/hwmon/applesmc.c
@@ -525,16 +525,25 @@ static int applesmc_init_smcreg_try(void)
 {
 	struct applesmc_registers *s = &smcreg;
 	bool left_light_sensor, right_light_sensor;
+	unsigned int count;
 	u8 tmp[1];
 	int ret;
 
 	if (s->init_complete)
 		return 0;
 
-	ret = read_register_count(&s->key_count);
+	ret = read_register_count(&count);
 	if (ret)
 		return ret;
 
+	if (s->cache && s->key_count != count) {
+		pr_warn("key count changed from %d to %d\n",
+			s->key_count, count);
+		kfree(s->cache);
+		s->cache = NULL;
+	}
+	s->key_count = count;
+
 	if (!s->cache)
 		s->cache = kcalloc(s->key_count, sizeof(*s->cache), GFP_KERNEL);
 	if (!s->cache)
-- 
1.8.3.4

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