netdev - Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads

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Message-ID: <20150829090701.GN20760@orbit.nwl.cc>
Date:	Sat, 29 Aug 2015 11:07:01 +0200
From:	Phil Sutter <phil@....cc>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, fengguang.wu@...el.com,
	wfg@...ux.intel.com, lkp@...org
Subject: Re: [PATCH 2/3] rhashtable-test: retry insert operations in threads

On Sat, Aug 29, 2015 at 12:43:03AM +0200, Thomas Graf wrote:
> On 08/28/15 at 03:34pm, Phil Sutter wrote:
> > Quite ugly, IMHO: rhashtable_insert_fast() may return -ENOMEM as
> > non-permanent error, if allocation in GFP_ATOMIC failed. In this case,
> > allocation in GFP_KERNEL is retried by rht_deferred_worker(). Sadly,
> > there is no way to determine if that has already been tried and failed.
> > 
> > The thread test triggers GFP_ATOMIC allocation failure quite easily, so
> > I can't really just ignore this issue. :)
> 
> Return EBUSY or ENOBUFS in the non-permanent case? It is definitely
> helpful if the API allows to differ between permanent and
> non-permanent errors.

Yes, indeed. Therefore rht_deferred_worker() needs to check the return
value of rhashtable_expand(). The question is how to propagate the error
condition, as the worker's return value is not being kept track of
(function returns void even).

Should we introduce a new field to struct rhashtable to track the
internal state? This might allow to clean up some rather obscure tests,
e.g. whether a table resize is in progress or not.

Cheers, Phil
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