From: Eric Dumazet <dada1@cosmosbay•com>
To: paulmck@linux•vnet.ibm.com
Cc: "David S. Miller" <davem@davemloft•net>,
Linux Netdev List <netdev@vger•kernel.org>
Subject: Re: [PATCH] net: remove superfluous call to synchronize_net()
Date: Thu, 16 Apr 2009 20:43:24 +0200 [thread overview]
Message-ID: <49E77C4C.5060508@cosmosbay.com> (raw)
In-Reply-To: <20090416180231.GI6924@linux.vnet.ibm.com>
Paul E. McKenney a écrit :
>
> Please add a comment where the synchronize_rcu() used to be explaining why
> it is not needed. The poor slob who copies your code isn't going to read
> theh Documentation/RCU, he is just going to expect it to magically work.
>
> With the synchronize_rcu(), it does just magically work. Without the
> synchronize_rcu(), you have to be careful. Therefore, please add the
> comment saying that care is required.
>
Sorry Paul, I dont understand why I should put a comment to say :
/*
* Dont need to use synchronize_net() or call_rcu() or msleep(100) or
* whatever function here because bla bla ...
*/
We could add this comment in about 99% of all functions in linux kernel ;)
I checked inet6_register_protosw(struct inet_protosw *p)
and it doesnt have this synchronize_rcu() neither the comment you advise...
Following construct is obvious and should not be commented in code itself.
spin_lock_bh(&somelock);
list_for_each(..., ...) {
if (some_condition) {
list_add_rcu(..., ...)
or rcu_assign_pointer(...)
break;
}
}
spin_unlock_bh(&somelock);
If it is not obvious, then it should be documented once in Documentation/RCU, since
we find hundred of similar code in kernel.
On the contrary, places where we *use* synchronize_{rcu|net}() should get a comment
to explain why this is really necessary since this function can be a real problem.
Thanks
next prev parent reply other threads:[~2009-04-16 18:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-15 15:38 [PATCH] net: remove superfluous call to synchronize_net() Eric Dumazet
2009-04-15 21:54 ` Paul E. McKenney
2009-04-16 5:40 ` Eric Dumazet
2009-04-16 15:52 ` Paul E. McKenney
2009-04-16 16:03 ` Eric Dumazet
2009-04-16 18:02 ` Paul E. McKenney
2009-04-16 18:43 ` Eric Dumazet [this message]
2009-04-17 11:56 ` David Miller
2009-04-17 19:25 ` Paul E. McKenney
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