On Mon, Nov 14, 2016 at 8:24 AM, Paul E. McKenney <paul...@linux.vnet.ibm.com> wrote: > On Sun, Nov 13, 2016 at 10:47:01PM -0800, Cong Wang wrote: >> On Fri, Nov 11, 2016 at 4:55 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote: >> > On Fri, Nov 11, 2016 at 4:23 PM, Paul E. McKenney >> > <paul...@linux.vnet.ibm.com> wrote: >> >> >> >> Ah! This net_mutex is different than RTNL. Should synchronize_net() be >> >> modified to check for net_mutex being held in addition to the current >> >> checks for RTNL being held? >> >> >> > >> > Good point! >> > >> > Like commit be3fc413da9eb17cce0991f214ab0, checking >> > for net_mutex for this case seems to be an optimization, I assume >> > synchronize_rcu_expedited() and synchronize_rcu() have the same >> > behavior... >> >> Thinking a bit more, I think commit be3fc413da9eb17cce0991f >> gets wrong on rtnl_is_locked(), the lock could be locked by other >> process not by the current one, therefore it should be >> lockdep_rtnl_is_held() which, however, is defined only when LOCKDEP >> is enabled... Sigh. >> >> I don't see any better way than letting callers decide if they want the >> expedited version or not, but this requires changes of all callers of >> synchronize_net(). Hm. > > I must confess that I don't understand how it would help to use an > expedited grace period when some other process is holding RTNL. > In contrast, I do well understand how it helps when the current process > is holding RTNL.
Yeah, this is exactly my point. And same for ASSERT_RTNL() which checks rtnl_is_locked(), clearly we need to assert "it is held by the current process" rather than "it is locked by whatever process". But given *_is_held() is always defined by LOCKDEP, so we probably need mutex to provide such a helper directly, mutex->owner is not always defined either. :-/
