Re: [PATCH 12/14] net: sched: retry action check-insert on concurrent modification

Jiri Pirko
2018-05-16T12:26:06Z

Wed, May 16, 2018 at 01:55:06PM CEST, vladbu@mellanox.com wrote:
>
>On Wed 16 May 2018 at 09:59, Jiri Pirko <jiri@resnulli.us> wrote:
>> Mon, May 14, 2018 at 04:27:13PM CEST, vladbu@mellanox.com wrote:
>>>Retry check-insert sequence in action init functions if action with same
>>>index was inserted concurrently.
>>>
>>>Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
>>>---
>>> net/sched/act_bpf.c | 8 +++++++-
>>> net/sched/act_connmark.c | 8 +++++++-
>>> net/sched/act_csum.c | 8 +++++++-
>>> net/sched/act_gact.c | 8 +++++++-
>>> net/sched/act_ife.c | 8 +++++++-
>>> net/sched/act_ipt.c | 8 +++++++-
>>> net/sched/act_mirred.c | 8 +++++++-
>>> net/sched/act_nat.c | 8 +++++++-
>>> net/sched/act_pedit.c | 8 +++++++-
>>> net/sched/act_police.c | 9 ++++++++-
>>> net/sched/act_sample.c | 8 +++++++-
>>> net/sched/act_simple.c | 9 ++++++++-
>>> net/sched/act_skbedit.c | 8 +++++++-
>>> net/sched/act_skbmod.c | 8 +++++++-
>>> net/sched/act_tunnel_key.c | 9 ++++++++-
>>> net/sched/act_vlan.c | 9 ++++++++-
>>> 16 files changed, 116 insertions(+), 16 deletions(-)
>>>
>>>diff --git a/net/sched/act_bpf.c b/net/sched/act_bpf.c
>>>index 5554bf7..7e20fdc 100644
>>>--- a/net/sched/act_bpf.c
>>>+++ b/net/sched/act_bpf.c
>>>@@ -299,10 +299,16 @@ static int tcf_bpf_init(struct net *net, struct nlattr *nla,
>>>
>>> parm = nla_data(tb[TCA_ACT_BPF_PARMS]);
>>>
>>>+replay:
>>> if (!tcf_idr_check(tn, parm->index, act, bind)) {
>>> ret = tcf_idr_create(tn, parm->index, est, act,
>>> &act_bpf_ops, bind, true);
>>>- if (ret < 0)
>>>+ /* Action with specified index was created concurrently.
>>>+ * Check again.
>>>+ */
>>>+ if (parm->index && ret == -ENOSPC)
>>>+ goto replay;
>>>+ else if (ret)
>>
>> Hmm, looks like you are doing the same/very similar thing in every act
>> code. I think it would make sense to introduce a helper function for
>> this purpose.
>
>This code uses goto so it can't be easily refactored into standalone
>function. Could you specify which part of this code you suggest to
>extract?

Hmm, looking at the code, I think that what would help is to have a
helper that would atomically check if index exists and if not, it would
allocate one. Something like:

int tcf_idr_check_alloc(struct tc_action_net *tn, u32 *index,
struct tc_action **a, int bind)
{
struct tcf_idrinfo *idrinfo = tn->idrinfo;
struct tc_action *p;
int err;

spin_lock(&idrinfo->lock);
if (*index) {
p = idr_find(&idrinfo->action_idr, *index);
if (p) {
if (bind)
p->tcfa_bindcnt++;
p->tcfa_refcnt++;
*a = p;
err = 0;
} else {
*a = NULL;
err = idr_alloc_u32(idr, NULL, index,
*index, GFP_ATOMIC);
}
} else {
*index = 1;
*a = NULL;
err = idr_alloc_u32(idr, NULL, index, UINT_MAX, GFP_ATOMIC);
}
spin_unlock(&idrinfo->lock);
return err;
}

The act code would just check if "a" is NULL and if so, it would call
tcf_idr_create() with allocated index as arg.

>
>>
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