netdev - Re: [PATCH net] 6lowpan: add missing fragment list spinlock

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Message-Id: <20140204.203203.1380460749447396879.davem@davemloft.net>
Date:	Tue, 04 Feb 2014 20:32:03 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	alex.aring@...il.com
Cc:	alex.bluesman.smirnov@...il.com, dbaryshkov@...il.com,
	linux-zigbee-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: [PATCH net] 6lowpan: add missing fragment list spinlock

From: Alexander Aring <alex.aring@...il.com>
Date: Tue,  4 Feb 2014 11:57:53 +0100

> @@ -197,7 +197,9 @@ static void lowpan_fragment_timer_expired(unsigned long entry_addr)
>  
>  	pr_debug("timer expired for frame with tag %d\n", entry->tag);
>  
> +	spin_lock_bh(&flist_lock);
>  	list_del(&entry->list);
> +	spin_unlock_bh(&flist_lock);
>  	dev_kfree_skb(entry->skb);
>  	kfree(entry);
>  }

This will deadlock, because the other code path holding flist_lock calls
del_timer_sync() to wait for this timer to return.

The synchornization in this code is really a big mess.
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