On Wed, Mar 29, 2017 at 06:29:10PM +0800, Gao Feng wrote: > Hi Pablo, > > > -----Original Message----- > > From: Pablo Neira Ayuso [mailto:pablo@xxxxxxxxxxxxx] > > Sent: Wednesday, March 29, 2017 6:08 PM > > To: gfree.wind@xxxxxxxxxxx > > Cc: netfilter-devel@xxxxxxxxxxxxxxx; Gao Feng <fgao@xxxxxxxxxx> > > Subject: Re: [PATCH nf-next v2 1/1] netfilter: helper: Remove useless rcu > lock > > when get expectfn > > > > On Wed, Mar 22, 2017 at 10:15:02AM +0800, gfree.wind@xxxxxxxxxxx wrote: > > > From: Gao Feng <fgao@xxxxxxxxxx> > > > > > > Because these two functions return the nf_ct_helper_expectfn pointer > > > which should be protected by rcu lock. So it should makes sure the > > > caller should hold the rcu lock, not inside these functions. > > > > > > Signed-off-by: Gao Feng <fgao@xxxxxxxxxx> > > > --- > > > v2: Shorter subject, per Pablo > > > v1: Initial version > > > > > > net/netfilter/nf_conntrack_helper.c | 6 ++---- > > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > > > diff --git a/net/netfilter/nf_conntrack_helper.c > > > b/net/netfilter/nf_conntrack_helper.c > > > index 6dc44d9..bce3d1f 100644 > > > --- a/net/netfilter/nf_conntrack_helper.c > > > +++ b/net/netfilter/nf_conntrack_helper.c > > > @@ -311,38 +311,36 @@ void nf_ct_helper_expectfn_unregister(struct > > > nf_ct_helper_expectfn *n) } > > > EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister); > > > > > > +/* Caller should hold the rcu lock */ > > > struct nf_ct_helper_expectfn * > > > nf_ct_helper_expectfn_find_by_name(const char *name) { > > > struct nf_ct_helper_expectfn *cur; > > > bool found = false; > > > > > > - rcu_read_lock(); > > > list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) { > > > if (!strcmp(cur->name, name)) { > > > found = true; > > > break; > > > } > > > } > > > - rcu_read_unlock(); > > > return found ? cur : NULL; > > > } > > > EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name); > > > > nf_ct_helper_expectfn_find_by_name() is called from ctnetlink, via > > ctnetlink_create_expect() and rcu read side lock is not held there. > There are two reasons. > 1. The rcu lock would be added in my patch " netfilter: helper: Add the rcu > lock when call __nf_conntrack_helper_find" for nf > https://patchwork.ozlabs.org/patch/741865/. If you have interdependencies between two patches like this, it's better to make it in one single go. > So the ctnetlink_create_expect would hold the rcu lock after apply that > patch. > > 2. Because these two functions return one pointer which needs RCU lock, so > the caller must hold rcu lock. > Or it still meets one error even though there is one rcu lock in these two > functions. > Because the memory which the returned pointer point to would be freed > already after rcu_read_unlock. > So the rcu lock is unnecessary in these functions. That's right. You're fixing up a real problem, no doubt. I'm just questioning that I think that if you are fixing up rcu locking, which seems to be the case, you just do it in one single patch. Thanks! -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
