rtnl lock

内核的接口很多都显式的要求在rtnl lock的保护下，它是一个mutex锁，用来保护netdevice等相关的数据，在内核，用户配置间的一致性。

定义在：net/core/rtnetlink.c

void rtnl_lock(void)
{
    mutex_lock(&rtnl_mutex);
}
EXPORT_SYMBOL(rtnl_lock);

Rohan Puri
This lock is used to serialize changes to net_device instances from runtime
events, conf changes

Yes, I understood this part, but I am wondering what is the purpose of
this lock. I am guessing it's to protect all network related
operations from critical events, for e.g.: protecting a packet
transmit during device removal, protecting routing table entry during
route lookup, etc., but I can't find its precise documentation

anywhere. Thanks,

What is rtnl mutex used for?

1 serializes all rtnetlink requests

2 serializes with other userspace apis (sysfs, ioctl, ...) to network configuration

3 protects list of net namespaces

As a consequence:

one request at a time, e.g. adding ip address must wait for user listing interface properties

dump requests (fib, tc classifier list, interfaces)... are also serialized

rtnl_mutex can be held for very long times:

schedule() (incl. GFP_KERNEL allocations) s

ynchronize_rcu(_net) rtnetlink: caveats

callbacks rely on rtnl mutex being held

rtnl_lock guarantees consistency during a dump

can’t blindly avoid rtnl mutex

allow to annotate handler: RTNL_DOIT_UNLOCKED

then start to push rtnl_lock down

https://lists.openfabrics.org/pipermail/general/2008-July/052458.html

https://lists.kernelnewbies.org/pipermail/kernelnewbies/2011-November/003979.html

https://www.netdevconf.org/2.2/slides/westphal-rtnlmutex-talk.pdf

ILD