Messages in this thread |  | | Subject | Re: 2.4.13pre5aa1 | From | Robert Love <> | Date | 19 Oct 2001 01:48:05 -0400 |
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On Fri, 2001-10-19 at 00:19, Andrea Arcangeli wrote: > Only in 2.4.13pre3aa1: 00_files_struct_rcu-2.4.10-04-1 > Only in 2.4.13pre5aa1: 00_files_struct_rcu-2.4.10-04-2
I want to point out to preempt-kernel users that RCU is not preempt-safe. The implicit locking assumed from per-CPU data structures is defeated by preemptibility.
(Actually, FWIW, I think I can think of ways to make RCU preemptible but it would involve changing the write-side quiescent code for the case where the pointers were carried over the task switches. Probably not worth it.)
This is not to say RCU is worthless with a preemptible kernel, but that we need to make it safe (and then make sure it is still a performance advantage, but I don't think this would add much overhead). Note this is clean, simply wrapping the read code in non-preemption statements.
I will hack up a patch when I get the time, but I would like to prevent myself from maintaining the patch against a third tree ... where, oh where, is 2.5? :)
Robert Love
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