Re: 2.6.33-rc1: WARNING: at kernel/mutex-debug.c:78 (geode hw rng?)

From: Andres Salomon
Date: Tue Dec 29 2009 - 18:22:40 EST


On Sun, 20 Dec 2009 01:44:56 +0100
Arnd Hannemann <hannemann@xxxxxxxxxxxxxxxxxxx> wrote:

> Hi,
>
> not so sure if it is geode related.
> While starting rngd on 2.6.33-rc1 on a geode machine, I got this
> warning:
>
> [ 19.545852] ------------[ cut here ]------------
> [ 19.547554] WARNING: at kernel/mutex-debug.c:78
> debug_mutex_unlock+0x78/0xb8()
> [ 19.547554] Modules linked in: ipt_LOG iptable_nat nf_nat
> nf_conntrack_ipv4 nf_conntrack nf_defrag_ipv4 arc4 ecb ath5k ehci_hcd
> ohci_hcd mac80211 ath
> [ 19.547554] Pid: 2509, comm: rngd Not tainted 2.6.33-rc1-ah0 #2
> [ 19.547554] Call Trace:
> [ 19.547554] [<c102d86c>] ? debug_mutex_unlock+0x78/0xb8
> [ 19.547554] [<c10168bd>] warn_slowpath_common+0x60/0x77
> [ 19.547554] [<c10168e1>] warn_slowpath_null+0xd/0x10
> [ 19.547554] [<c102d86c>] debug_mutex_unlock+0x78/0xb8
> [ 19.547554] [<c1273314>] __mutex_unlock_slowpath+0x7b/0xa3
> [ 19.547554] [<c1273344>] mutex_unlock+0x8/0xa
> [ 19.547554] [<c116de8c>] rng_dev_read+0x13b/0x156
> [ 19.547554] [<c116dd51>] ? rng_dev_read+0x0/0x156
> [ 19.547554] [<c105ac23>] vfs_read+0x8a/0x11a
> [ 19.547554] [<c105af18>] sys_read+0x3b/0x60
> [ 19.547554] [<c127426d>] syscall_call+0x7/0xb
> [ 19.547554] ---[ end trace cd1825d2e719f82e ]---
>
> however, the system seems stable, and the hwrng seems to work fine...
>
> Best regards,
> Arnd


Hm, I suspect that 9996508b is the culprit. Does the following patch
help?



Subject: [PATCH] hw_random: don't attempt to unlock mutex twice

Commit 9996508b reworked rng_dev_read such that we unlock rng_mutex
after exiting the loop; however, we also unlock it inside the loop
before exiting. The out_unlock label should only be reached manually.

This code is starting to reach goto-considered-harmful territory. :/

Signed-off-by: Andres Salomon <dilinger@xxxxxxxxxxxxxxx>
---
drivers/char/hw_random/core.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index e989f67..29a5f6a 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -157,6 +157,9 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
err = -ERESTARTSYS;
goto out;
}
+
+ if (!size)
+ goto out;
}
out_unlock:
mutex_unlock(&rng_mutex);
--
1.5.6.5



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