netdev - RE: [PATCH 1/2] rhashtable: Introduce rhashtable_walk

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CAD3B6C@AcuExch.aculab.com>
Date:	Tue, 27 Jan 2015 10:09:18 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Herbert Xu' <herbert@...dor.apana.org.au>
CC:	Thomas Graf <tgraf@...g.ch>, Ying Xue <ying.xue@...driver.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"kaber@...sh.net" <kaber@...sh.net>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>
Subject: RE: [PATCH 1/2] rhashtable: Introduce rhashtable_walk_*

From: Herbert Xu 
> On Mon, Jan 26, 2015 at 10:09:24AM +0000, David Laight wrote:
> >
> > That doesn't look right to me.
> > Surely you shouldn't be calling rcu_read_lock() when the mutex
> > request is interrupted.
> >
> > So maybe:
> > 	err = mutex_lock_interruptible(&ht->mutex);
> > 	if (err)
> > 		return err;
> > 	rcu_read_lock();
> 
> No, we need to grab the RCU read lock while holding the mutex
> in order to prevent future resizes from happening once we release
> the mutex.

But if err is non-zero you don't hold the mutex.
Presumably the calling code also errors out immediately,
so the RCU lock isn't needed at all.

	David

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