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Message-ID: <20170923212124.GD4324@breakpoint.cc>
Date: Sat, 23 Sep 2017 23:21:24 +0200
From: Florian Westphal <fw@...len.de>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 3/6] rtnetlink: add helper to dump ifalias
Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Sat, 2017-09-23 at 21:26 +0200, Florian Westphal wrote:
> > Reviewed-by: David Ahern <dsahern@...il.com>
> > Signed-off-by: Florian Westphal <fw@...len.de>
> > ---
> > Changes since v3: don't add rtnl assertion, I placed the assertion
> > in my working tree instead as a reminder.
> >
> > net/core/rtnetlink.c | 11 +++++++++--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> > index c801212ee40e..47c17c3de79a 100644
> > --- a/net/core/rtnetlink.c
> > +++ b/net/core/rtnetlink.c
> > @@ -1332,6 +1332,14 @@ static int nla_put_iflink(struct sk_buff *skb, const struct net_device *dev)
> > return nla_put_u32(skb, IFLA_LINK, ifindex);
> > }
> >
> > +static noinline int nla_put_ifalias(struct sk_buff *skb, struct net_device *dev)
>
>
> Why noinline here ?
>
> This function does not use stack at all (and that would call for
> noinline_for_stack )
>
> > +{
> > + if (dev->ifalias)
> > + return nla_put_string(skb, IFLA_IFALIAS, dev->ifalias);
> > +
> > + return 0;
> > +}
> > +
>
> I really do not see the point of not making this RCU aware right away,
> or at least make it in the same patch series...
I saw no point to mix these refactoring with actual change :-|
(and it doesn't help either as-is with netlink dumping, only sysfs path can
elide rtnl).
Subject: [PATCH net-next] net: core: decouple ifalias get/set from rtnl lock
Device alias can be set by either rtnetlink (rtnl is held) or sysfs.
rtnetlink holds rtnl mutex, sysfs acquires it for this purpose.
Add a new mutex for it plus a seqcount to get a consistent snapshot
of the alias buffer.
This allows the sysfs path to not take rtnl and would later allow
to not hold it when dumping ifalias.
Signed-off-by: Florian Westphal <fw@...len.de>
---
include/linux/netdevice.h | 3 +-
net/core/dev.c | 70 +++++++++++++++++++++++++++++++++++++++--------
net/core/net-sysfs.c | 14 ++++------
net/core/rtnetlink.c | 7 +++--
4 files changed, 70 insertions(+), 24 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f535779d9dc1..0bcedb498f6f 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1632,7 +1632,7 @@ enum netdev_priv_flags {
struct net_device {
char name[IFNAMSIZ];
struct hlist_node name_hlist;
- char *ifalias;
+ char __rcu *ifalias;
/*
* I/O specific fields
* FIXME: Merge these and struct ifmap into one
@@ -3275,6 +3275,7 @@ void __dev_notify_flags(struct net_device *, unsigned int old_flags,
unsigned int gchanges);
int dev_change_name(struct net_device *, const char *);
int dev_set_alias(struct net_device *, const char *, size_t);
+int dev_get_alias(const struct net_device *, char *, size_t);
int dev_change_net_namespace(struct net_device *, struct net *, const char *);
int __dev_set_mtu(struct net_device *, int);
int dev_set_mtu(struct net_device *, int);
diff --git a/net/core/dev.c b/net/core/dev.c
index 97abddd9039a..92d87b4a2db1 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -188,6 +188,9 @@ static struct napi_struct *napi_by_id(unsigned int napi_id);
DEFINE_RWLOCK(dev_base_lock);
EXPORT_SYMBOL(dev_base_lock);
+static DEFINE_MUTEX(ifalias_mutex);
+static seqcount_t ifalias_rename_seq;
+
/* protects napi_hash addition/deletion and napi_gen_id */
static DEFINE_SPINLOCK(napi_hash_lock);
@@ -1265,29 +1268,72 @@ int dev_change_name(struct net_device *dev, const char *newname)
*/
int dev_set_alias(struct net_device *dev, const char *alias, size_t len)
{
- char *new_ifalias;
-
- ASSERT_RTNL();
+ char *new_ifalias, *old_ifalias;
if (len >= IFALIASZ)
return -EINVAL;
+ mutex_lock(&ifalias_mutex);
+
+ old_ifalias = rcu_dereference_protected(dev->ifalias,
+ mutex_is_locked(&ifalias_mutex));
if (!len) {
- kfree(dev->ifalias);
- dev->ifalias = NULL;
- return 0;
+ RCU_INIT_POINTER(dev->ifalias, NULL);
+ goto out;
}
- new_ifalias = krealloc(dev->ifalias, len + 1, GFP_KERNEL);
- if (!new_ifalias)
+ new_ifalias = __krealloc(old_ifalias, len + 1, GFP_KERNEL);
+ if (!new_ifalias) {
+ mutex_unlock(&ifalias_mutex);
return -ENOMEM;
- dev->ifalias = new_ifalias;
- memcpy(dev->ifalias, alias, len);
- dev->ifalias[len] = 0;
+ }
+ if (new_ifalias == old_ifalias) {
+ write_seqcount_begin(&ifalias_rename_seq);
+ memcpy(new_ifalias, alias, len);
+ new_ifalias[len] = 0;
+ write_seqcount_end(&ifalias_rename_seq);
+ mutex_unlock(&ifalias_mutex);
+ return len;
+ }
+
+ memcpy(new_ifalias, alias, len);
+ new_ifalias[len] = 0;
+
+ rcu_assign_pointer(dev->ifalias, new_ifalias);
+out:
+ mutex_unlock(&ifalias_mutex);
+ if (old_ifalias) {
+ synchronize_net();
+ kfree(old_ifalias);
+ }
return len;
}
+int dev_get_alias(const struct net_device *dev, char *alias, size_t len)
+{
+ unsigned int seq;
+ int ret;
+
+ for (;;) {
+ const char *name;
+
+ ret = 0;
+ rcu_read_lock();
+ name = rcu_dereference(dev->ifalias);
+ seq = raw_seqcount_begin(&ifalias_rename_seq);
+ if (name)
+ ret = snprintf(alias, len, "%s", name);
+ rcu_read_unlock();
+
+ if (!read_seqcount_retry(&ifalias_rename_seq, seq))
+ break;
+
+ cond_resched();
+ }
+
+ return ret;
+}
/**
* netdev_features_change - device changes features
@@ -8749,6 +8795,8 @@ static int __init net_dev_init(void)
NULL, dev_cpu_dead);
WARN_ON(rc < 0);
rc = 0;
+
+ seqcount_init(&ifalias_rename_seq);
out:
return rc;
}
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 927a6dcbad96..530de7996d65 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -391,10 +391,7 @@ static ssize_t ifalias_store(struct device *dev, struct device_attribute *attr,
if (len > 0 && buf[len - 1] == '\n')
--count;
- if (!rtnl_trylock())
- return restart_syscall();
ret = dev_set_alias(netdev, buf, count);
- rtnl_unlock();
return ret < 0 ? ret : len;
}
@@ -403,13 +400,12 @@ static ssize_t ifalias_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
const struct net_device *netdev = to_net_dev(dev);
+ char tmp[IFALIASZ];
ssize_t ret = 0;
- if (!rtnl_trylock())
- return restart_syscall();
- if (netdev->ifalias)
- ret = sprintf(buf, "%s\n", netdev->ifalias);
- rtnl_unlock();
+ ret = dev_get_alias(netdev, tmp, sizeof(tmp));
+ if (ret > 0)
+ ret = sprintf(buf, "%s\n", tmp);
return ret;
}
static DEVICE_ATTR_RW(ifalias);
@@ -1488,7 +1484,7 @@ static void netdev_release(struct device *d)
BUG_ON(dev->reg_state != NETREG_RELEASED);
- kfree(dev->ifalias);
+ dev_set_alias(dev, "", 0);
netdev_freemem(dev);
}
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index c69451964a44..bab108ced7d8 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1368,10 +1368,11 @@ static int nla_put_iflink(struct sk_buff *skb, const struct net_device *dev)
static noinline int nla_put_ifalias(struct sk_buff *skb, struct net_device *dev)
{
- if (dev->ifalias)
- return nla_put_string(skb, IFLA_IFALIAS, dev->ifalias);
+ char buf[IFALIASZ];
+ int ret;
- return 0;
+ ret = dev_get_alias(dev, buf, sizeof(buf));
+ return ret > 0 ? nla_put_string(skb, IFLA_IFALIAS, buf) : 0;
}
static noinline int rtnl_fill_link_netnsid(struct sk_buff *skb,
--
2.13.5
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