On Mon, Nov 14, 2016 at 09:44:35AM -0800, Cong Wang wrote: > 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. :-/
There is always the option of making acquisition and release set a per-task variable that can be tested. (Where did I put that asbestos suit, anyway?) Thanx, Paul