Re: [Patch] net: allow calling rtmsg_ifinfo() in atomic

On Tue, 2012-08-14 at 18:28 +0800, Cong Wang wrote:

(Against net tree.)

When running 'systemctl restart network.service', I got the following
warning:

 [ 1123.199677] 
 [ 1123.310275] ===============================
 [ 1123.442202] [ INFO: suspicious RCU usage. ]
 [ 1123.558207] 3.6.0-rc1+ #109 Not tainted
 [ 1123.665204] -------------------------------
 [ 1123.768254] include/linux/rcupdate.h:430 Illegal context switch in RCU read-side critical section!
 [ 1123.992320] 
 [ 1123.992320] other info that might help us debug this:
 [ 1123.992320] 
 [ 1124.307382] 
 [ 1124.307382] rcu_scheduler_active = 1, debug_locks = 0
 [ 1124.522220] 2 locks held by sysctl/5710:
 [ 1124.648364]  #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff81768498>] rtnl_trylock+0x15/0x17
 [ 1124.882211]  #1:  (rcu_read_lock){.+.+.+}, at: [<ffffffff81871df8>] rcu_lock_acquire+0x0/0x29

[...]

This is due to that we call rtmsg_ifinfo() with RCU read lock held,
and because rtmsg_ifinfo() may block, this is invalid.

This patch fixes it by allowing callees to specify GFP when
calling it. In this case, netdev_features_change() calls it
with GFP_ATOMIC.

[...]

This is not the right fix; netdev notifiers *should* be able to assume
they are called with only the RTNL lock held.  Anyway,
addrconf_forward_change() is called with the RTNL lock held so there is
no need for it to use RCU-protected iteration.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.