Re: [RFC][PATCH] (#7U5) [2-6.12-rc3-mm3] file system auditing
Quoting Timothy R. Chavez (tinytim(a)us.ibm.com):
On Wednesday 11 May 2005 14:01, serue(a)us.ibm.com wrote:
> Quoting Timothy R. Chavez (tinytim(a)us.ibm.com):
> > * I've completely removed the audit_master_watchlist_lock spinlock to
> > protect the master watchlist, in favor of RCU locking. ?To protect
> > against concurrent watch removals from the master watchlist, we
> > conveniently use the local data->lock rw_lock in place of another
> > spinlock. ?Thus, only one removal can
>
> I have a problem with this. Isn't the audit_master_watchlist a global
> list? Are you sure you can use a per-inode lock to protect this global
> list?
Well, my conclusion was this: The only way to enter audit_destroy_wentry()
where contention is a concern is by holding the local data->lock. The only
way we can remove a watch from the master watchlist is by entering the
audit_destroy_wentry() function (and if contentious, only one of the
contenders may be in audit_destroy_wentry() at a time).
I don't see how we could race on a master watchlist deletion.
1. What if you end up trying to delete two wentries which are adjecent
on the audit_master_watchlist concurrently? I think you might be able
to break the list, but I haven't drawn it down on paper...
2. What about additions to the audit_master_watchlist, both racing with
each other and with deletions? Actually it doesn't look like you're
protecting additions at all.
-serge