On Thu, Jan 11, 2007 at 09:42:13AM -0800, Stephen Hemminger wrote:

Paul McKenney has given lots of talks on RCU see:
	http://www.rdrop.com/users/paulmck/RCU/

and look in Documentation/RCU

 
I've read a lot of this but it's sometimes confusing e.g.:

From Documentation/RCU/checklist.txt:

9.      All RCU list-traversal primitives, which include
       list_for_each_rcu(), list_for_each_entry_rcu(),
       list_for_each_continue_rcu(), and list_for_each_safe_rcu(),
       must be within an RCU read-side critical section.  RCU
       read-side critical sections are delimited by rcu_read_lock()
       and rcu_read_unlock(), or by similar primitives such as
       rcu_read_lock_bh() and rcu_read_unlock_bh().

So "All" and "must be"!

       Use of the _rcu() list-traversal primitives outside of an
       RCU read-side critical section causes no harm other than
       a slight performance degradation on Alpha CPUs.  It can
       also be quite helpful in reducing code bloat when common
       code is shared between readers and updaters.

... or not all and not must be?


I think, probably because of examples in those docs -  mostly with 
spin_locks (or without preemption), I've got wrong conviction that
writers (or more often readers and writers) in their reading part
aren't allowed to be preempted or block also. But after rethinking
yesterday explanation of David Miller I undestood the writers have
more possibilities and individual analyzis is required each time.

Many thanks once more to everyone,

Jarek P.