Re: Fwd: IGMP and rwlock: Dead ocurred again on TILEPro

[AmÃrico Wang]

On Thu, Feb 17, 2011 at 01:04:14PM +0800, Cypher Wu wrote:
>>
>> Have you turned CONFIG_LOCKDEP on?
>>
>> I think Eric already converted that rwlock into RCU lock, thus
>> this problem should disappear. Could you try a new kernel?
>>
>> Thanks.
>>
>
>I haven't turned CONFIG_LOCKDEP on for test since I didn't get too
>much information when we tried to figured out the former deadlock.
>
>IGMP used read_lock() instead of read_lock_bh() since usually
>read_lock() can be called recursively, and today I've read the
>implementation of MIPS, it's should also works fine in that situation.
>The implementation of TILEPro cause problem since after it use TNS set
>the lock-val to 1 and hold the original value and before it re-set
>lock-val a new value, it a race condition window.
>

I see no reason why you can't call read_lock_bh() recursively,
read_lock_bh() is roughly equalent to local_bh_disable() + read_lock(),
both can be recursive.

But I may miss something here. :-/
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