linux-kernel - Re: My system stops during startup with curretn git tree of 2.6.25-rc2

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Date:	Mon, 18 Feb 2008 14:44:29 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Laszlo Attila Toth <panther@...abit.hu>
cc:	David Miller <davem@...emloft.net>, zdenek.kabelac@...il.com,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: My system stops during startup with curretn git tree of 2.6.25-rc2

On Mon, 18 Feb 2008, Laszlo Attila Toth wrote:

> Okay, but I can't figure out what's the problem with it. I don't have 
> wireless card on my linux box also I can't test it but everything else 
> works. Swap is mounted. The concurrency cannot be a problem because the 
> write operation is protected by a lock.

-               write_lock_bh(&dev_base_lock);
-               dev->link_mode = nla_get_u8(tb[IFLA_LINKMODE]);
-               write_unlock_bh(&dev_base_lock);
+               if (dev->link_mode != nla_get_u8(tb[IFLA_LINKMODE])) {
+                       write_lock_bh(&dev_base_lock);
+                       dev->link_mode = nla_get_u8(tb[IFLA_LINKMODE]);
+                       write_lock_bh(&dev_base_lock);
+                       modified = 1;
+               }
        }

1) you are accessing dev->link_mode and tb[] outside the dev_base_lock 
2) there is obvious and immediate deadlock -- you acquire the 
   dev_base_lock twice, without any unlock, just look at the chunk above
3) even with this deadlock fixed, Rafael states that either NM or 
   wpa_supplicant (I don't recall from top of my head) still don't work

-- 
Jiri Kosina
SUSE Labs
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