On 2022-12-16 06:41, Zhenlei Huang wrote:
While hacking `sys/kern/kern_jail.c` I got lost.
There're lots of ref / unref and flags to prevent visit invalid prison
while
concurrent modification is possible and some refs looks weird.
Is it possible to employ epoch(9) to simplify managing of prison
lifecycle ?
I imagine it could be used, though I'm not sure offhand if it would make
things more or less complicated. There are two issues with the
prison_deref flags (which I assume you're talking about):
Much of it is tracking whether/how the allprison_lock is held, and I
don't see that changing. I want to make sure it remains locked as long
as a half-formed prison is in the list, but I also want at least the
exclusive holds to be as short as possible. I probably don't want to
wait for some epoch timeout to remove something that's not in a usable
state, and it doesn't seem right to keep hold of an exclusive lock until
then.
The other complexity is the two different kinds of reference counts,
pr_uref for user-level visibility, and pr_ref for existing at all (and
each with its prison_deref flag). I don't think that will change with
epochs.
I'm not very familiar with epoch(9), having only run into it by watching
(but not really participating in) the changes with IP address lists
falling under the network epoch. So there's probably more to the
underlying concept that what little I got from that, and from a perusal
of the man page.
- Jamie
