netdev - Re: [PATCH net-next v2] rhashtable: unnecessary to use delayed work

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Date:	Wed, 14 Jan 2015 17:29:56 +0800
From:	Ying Xue <ying.xue@...driver.com>
To:	Thomas Graf <tgraf@...g.ch>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2] rhashtable: unnecessary to use delayed work

On 01/14/2015 05:24 PM, Thomas Graf wrote:
> On 01/14/15 at 11:32am, Ying Xue wrote:
>> When we put our declared work task in the global workqueue with
>> schedule_delayed_work(), its delay parameter is always zero.
>> Therefore, we should define a normal work in rhashtable structure
>> instead of a delayed work.
>>
>> By the way, we add a condition to check whether resizing functions
>> are NULL before cancel the work, avoiding to cancel an uninitialized
>> work.
>>
>> Lastly, while we wait for all work items we submitted before to run
>> to completion with cancel_delayed_work(), ht->mutex has been taken in
>> rhashtable_destroy(). Moreover, cancel_delayed_work() doesn't return
>> until all work items are accomplished, and when work items are
>> scheduled, the work's function - rht_deferred_worker() will be called.
>> However, as rht_deferred_worker() also needs to acquire the lock,
>> deadlock might happen at the moment as the lock is already held before.
>> So if the cancel work function is moved out of the lock covered scope,
>> this can help to avoid the deadlock.
>   ^^^^^^^^^^^^^^^
>   will avoid :-)
> 
>>
>> Fixes: 97defe1 ("rhashtable: Per bucket locks & deferred expansion/shrinking")
>> Signed-off-by: Ying Xue <ying.xue@...driver.com>
>> Cc: Thomas Graf <tgraf@...g.ch>
> 
> I don't want to be too picky about the commit title but since this is
> fixing a previously reported race condition I would like for that to
> be reflected in the title. Something like:
> 
> rhashtable: Fix race in rhashtable_destroy() and use regular work_struct
> 
> With that fixed:
> Acked-by: Thomas Graf <tgraf@...g.ch>
> 
> 

Thanks for the review, and I will deliver the v3 soon.

Regards,
Ying

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