netdev - Re: [PATCH] inet: frags: Remove unnecessary smp_store_release/READ

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Message-Id: <20190530.115154.102635044166921930.davem@davemloft.net>
Date:   Thu, 30 May 2019 11:51:54 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     herbert@...dor.apana.org.au
Cc:     edumazet@...gle.com, netdev@...r.kernel.org,
        eric.dumazet@...il.com, syzkaller@...glegroups.com
Subject: Re: [PATCH] inet: frags: Remove unnecessary
 smp_store_release/READ_ONCE

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Wed, 29 May 2019 13:40:26 +0800

> The smp_store_release call in fqdir_exit cannot protect the setting
> of fqdir->dead as claimed because its memory barrier is only
> guaranteed to be one-way and the barrier precedes the setting of
> fqdir->dead.
> 
> IOW it doesn't provide any barriers between fq->dir and the following
> hash table destruction.
> 
> In fact, the code is safe anyway because call_rcu does provide both
> the memory barrier as well as a guarantee that when the destruction
> work starts executing all RCU readers will see the updated value for
> fqdir->dead.
> 
> Therefore this patch removes the unnecessary smp_store_release call
> as well as the corresponding READ_ONCE on the read-side in order to
> not confuse future readers of this code.  Comments have been added
> in their places.
> 
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

Applied.